Geotechnical engineering procedures for foundation

UFC 3-220-01N
15 AUGUST 2005
UNIFIED FACILITIES CRITERIA (UFC)
GEOTECHNICAL ENGINEERING
PROCEDURES FOR FOUNDATION
DESIGN OF BUILDINGS AND
STRUCTURES
APPROVED FOR PUBLIC RELEASE; DISTRIBUTION UNLIMITED

UFC 3-220-01N
15 AUGUST 2005
UNIFIED FACILITIES CRITERIA (UFC)
GEOTECHNICAL ENGINEERING PROCEDURES FOR FOUNDATION DESIGN OF
BUILDINGS AND STRUCTURES
Any copyrighted material included in this UFC is identified at its point of use.
Use of the copyrighted material apart from this UFC must have the permission of the
copyright holder.
U.S. ARMY CORPS OF ENGINEERS
NAVAL FACILITIES ENGINEERING COMMAND (Preparing Activity)
AIR FORCE CIVIL ENGINEER SUPPORT AGENCY
Record of Changes (changes are indicated by 1 ... /1/)
Change No. Date Location
_____________
This UFC supersedes DM 7.01, DM 7.02, and DM-38.4.
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FOREWORD
The Unified Facilities Criteria (UFC) system is prescribed by MIL-STD 3007 and provides
planning, design, construction, sustainment, restoration, and modernization criteria, and applies
to the Military Departments, the Defense Agencies, and the DoD Field Activities in accordance
with USD(AT&L) Memorandum dated 29 May 2002. UFC will be used for all DoD projects and
work for other customers where appropriate. All construction outside of the United States is
also governed by Status of forces Agreements (SOFA), Host Nation Funded Construction
Agreements (HNFA), and in some instances, Bilateral Infrastructure Agreements (BIA.)
Therefore, the acquisition team must ensure compliance with the more stringent of the UFC, the
SOFA, the HNFA, and the BIA, as applicable.
UFC are living documents and will be periodically reviewed, updated, and made available to
users as part of the Services’ responsibility for providing technical criteria for military
construction. Headquarters, U.S. Army Corps of Engineers (HQUSACE), Naval Facilities
Engineering Command (NAVFAC), and Air Force Civil Engineer Support Agency (AFCESA) are
responsible for administration of the UFC system. Defense agencies should contact the
preparing service for document interpretation and improvements. Technical content of UFC is
the responsibility of the cognizant DoD working group. Recommended changes with supporting
rationale should be sent to the respective service proponent office by the following electronic
form: Criteria Change Request (CCR). The form is also accessible from the Internet sites listed
below.
UFC are effective upon issuance and are distributed only in electronic media from the following
source:
• Whole Building Design Guide web site http://dod.wbdg.org/.
Hard copies of UFC printed from electronic media should be checked against the current
electronic version prior to use to ensure that they are current.
AUTHORIZED BY:
______________________________________
DONALD L. BASHAM, P.E.
Chief, Engineering and Construction
U.S. Army Corps of Engineers
______________________________________
DR. JAMES W WRIGHT, P.E.
Chief Engineer
Naval Facilities Engineering Command
______________________________________
KATHLEEN I. FERGUSON, P.E.
The Deputy Civil Engineer
DCS/Installations & Logistics
Department of the Air Force
______________________________________
Dr. GET W. MOY, P.E.
Director, Installations Requirements and
Management
Office of the Deputy Under Secretary of Defense
(Installations and Environment)
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CONTENTS
Page
CHAPTER 1 INTRODUCTION
Paragraph 1-1 PURPOSE................................................................................1-1
1-2 SCOPE.....................................................................................1-1
1-3 REFERENCES.........................................................................1-1
1-4 GENERAL GUIDANCE ............................................................1-1
1-4.1 Content Guidance ....................................................................1-1
CHAPTER 2 SOILS AND GEOLOGY
Paragraph 2-1 INTRODUCTION......................................................................2-1
2-1.1 Purpose....................................................................................2-1
2-1.2 Scope .......................................................................................2-1
2-1.3 References...............................................................................2-1
CHAPTER 3 SELECTION OF FOUNDATION TYPES
Paragraph 3-1 SELECTION OF FOUNDATION TYPE ....................................3-1
3-1.1 Foundation Selection Consideration.........................................3-1
3-1.2 Adverse Subsurface Conditions ...............................................3-2
3-1.3 Cost Estimates and Final Selection..........................................3-2
CHAPTER 4 SHALLOW FOUNDATIONS
4-1.1 Purpose....................................................................................4-1
4-1.2 Scope .......................................................................................4-1
4-1.3 Related Criteria ........................................................................4-1
4-1.4 References...............................................................................4-1
4-1.5 Secondary References.............................................................4-1
CHAPTER 5 DEEP FOUNDATIONS
5-1.1 Purpose....................................................................................5-1
5-1.2 Scope .......................................................................................5-1
5-1.3 Related Criteria ........................................................................5-1
5-1.4 References...............................................................................5-1
CHAPTER 6 RETAINING WALLS AND CELLULAR COFFERDAMS
6-1.1 Purpose....................................................................................6-1
6-1.2 Scope .......................................................................................6-1
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CHAPTER 4
SHALLOW FOUNDATIONS
4-1 INTRODUCTION
4-1.1 Purpose. This chapter presents guidance for selecting and designing
shallow foundations for buildings and structures. Shallow foundations are those that
bear at a Depth of bearing/Base (D/B) width of footing equal to less than 5. The
referenced criteria are to be used by the engineer to develop the bearing capacity,
settlement potential and size of shallow foundations for buildings or structures.
4-1.2 Scope. Apply criteria to all projects for the military services. The methods
for determining the ability to use a shallow foundation, settlement potential (the most
important factor in shallow foundation design) allowable soil bearing capacity as limited
by shear strength, and the size of the foundation are presented in referenced criteria.
The allowable settlement tolerances for structures are covered in the primary
references.
4-1.3 Related Criteria. Reference Chapters 8, "Excavation, Fill, Backfill, and
Soil Stabilitization For Structures," Chapter 10, "Foundations in Expansive Soils," and
Chapter 11 "Foundations in Areas of Significant Frost Penetration" and Chapter 12
"Foundations for Vibrating Equipment and Seismic Loadings" when designing shallow
foundations when any of the factors, excavations, soil stabilization, expansive soils,
seismic situations, vibration or significant frost penetration are present for a particular
site.
4-1.4 References. These present load factor and safety factor design methods
and should be used as a unit. Last reference presents safety factor design and the
classic design procedures.
• Engineering Manual for Shallow Foundations, Driven Piles, Drilled
Shafts, Retaining Walls and Abutments
• Engineering Manual for Settlement Studies
• Shear Strength Correlation for Geotechnical Engineering
• UFC 3-220-10N, Soil Mechanics
4-1.5 Secondary References
• American Society of Civil Engineers, Settlement Analysis, Technical
Engineering and Design Guides
• American Society of Civil Engineers, Design of Shallow Foundations
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8-6 SPECIFICATION PROVISIONS.............................................. 8-77
8-6.1 General ................................................................................... 8-77
8-6.2 Preparation of Specifications................................................... 8-77
8-6.3 Foundation Preparation........................................................... 8-79
8-6.4 Backfill Operations ..................................................................8-79
8-7 STABILIZATION OF SUBGRADE SOILS ............................... 8-81
8-7.1 General ................................................................................... 8-81
8-7.2 Vibrocompaction......................................................................8-81
8-7.3 Vibrodisplacement Compaction............................................... 8-82
8-7.4 Grouting and Injection ............................................................. 8-98
8-7.5 Precompression ......................................................................8-99
8-7.6 Reinforcement....................................................................... 8-102
8-7.7 Miscellaneous Methods......................................................... 8-104
CHAPTER 9 DEWATERING AND GROUNDWATER CONTROL
9-1.1 Purpose....................................................................................9-1
9-1.2 Scope .......................................................................................9-1
9-1.3 References...............................................................................9-1
CHAPTER 10 FOUNDATIONS IN EXPANSIVE SOILS
Paragraph 10-1 INTRODUCTION....................................................................10-1
10-1.1 Purpose..................................................................................10-1
10-1.2 Scope .....................................................................................10-1
10-1.3 References.............................................................................10-1
CHAPTER 11FOUNDATIONS IN AREAS OF SIGNIFICANT FRONT PENETRATION
11-1.1 Types of Areas .......................................................................11-1
11-1.2 General Nature of Design Problems.......................................11-2
11-2 FACTORS AFFECTING DESIGN OF FOUNDATIONS .........11-4
11-2.1 Physiography and Geology ....................................................11-4
11-2.2 Temperature...........................................................................11-4
11-2.3 Foundation Materials..............................................................11-5
11-2.4 Water Conditions....................................................................11-7
11-2.5 Frost Heave and Effect of Surcharge .....................................11-7
11-2.6 Type pf Structure....................................................................11-7
11-3 SITE INVESTIGATIONS ........................................................11-7
11-3.1 General...................................................................................11-7
11-3.2 Remote Sensing and Geophysical Investigations ..................11-8
11-3.3 Direct Site Investigations........................................................11-8
11-4 FOUNDATION DESIGN....................................................... 11-9
11-4.1 Selection of Foundation Type............................................... 11-9
11-4.2 Foundation Freeze and Thaw and Techniques for Control.. 11-11
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11-4.3 Control of Movement and Distortion .................................... 11-14
11-4.4 Vibration Problems and Seismic Effects.............................. 11-15
11-4.5 Design Criteria for Various Specific Features...................... 11-16
CHAPTER 12 FOUNDATIONS FOR VIBRATING EQUIPEMENT AND
SEISMIC LOADINGS
12-1.1 Introduction.............................................................................12-1
12-1.2 Single Degree of Freedom, Damped Force Systems .............12-1
12-1.3 Foundations on Elastic Soils ..................................................12-3
12-1.4 Wave Transmission, Attenuation and Isolation.....................12-12
12-1.5 Evaluation of S-wave Velocity in Soils..................................12-14
12-1.6 Settlement and Liquefaction.................................................12-22
12-1.7 Seismic Effects on Foundations ...........................................12-25
CHAPTER 13 PILE DRIVING EQUIPMENT
13-1.1 Purpose..................................................................................13-1
13-1.2 Scope .....................................................................................13-1
13-1.3 References.............................................................................13-1
CHAPTER 14 GROUTING METHODS AND EQUIPMENT
14-1.1 Purpose..................................................................................14-1
14-1.2 Scope .....................................................................................14-1
14-1.3 References.............................................................................14-1
APPENDIX A REFERENCES….……………………………………………..… A-1
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FIGURES
Figure Title
6-1 Design Criteria for Cellular Cofferdams........................................................6-3
8-1.1 Sliding Trench Shield ...................................................................................8-7
8-1.2 Skeleton Shoring....................................................................................... 8-9
8-1.3 Close (Tight) Sheeting .............................................................................. 8-9
8-1.4 Box Shoring............................................................................................... 8-10
8-1.5 Telescopic Shoring.................................................................................... 8-10
8-1.6 General Guidance for Underpinning.......................................................... 8-11
8-1.7 Rippability of Subsurface Materials Related to Longitudinal Seismic
Velocity for a Heavy Duty Ripper (Tractor-Mounted)................................. 8-14
8-1.8 Suggested Guide for Ease of Excavation.................................................. 8-14
8-1.9 Cube Root Scaling Versus Maximum Particle Velocity ............................. 8-15
8-1.10 Guideline for Assessing Potential for Damage Induced by Blasting
Vibration to Residential Structure Founded on Dense Soil or Rock .......... 8-16
8-1.11 Guide for Predicting Human Respose to Vibrations and Blast Effects ...... 8-16
8-1.12 Resistance of Earth Dam, Embankment Materials To Piping and
Cracking.................................................................................................... 8-27
8-3.1 Open Backfill Zones .................................................................................. 8-42
8-3.2 Confined Backfill Zones ............................................................................ 8-43
8-3.3 Complex Structures................................................................................... 8-44
8-3.4 Excavation Subject to Bottom Heave........................................................ 8-46
8-3.5 Excess Lateral Pressure Against Vertical Walls Induced by Compaction . 8-47
8-7.1 Applicable Grain-size Ranges for Different Stabilization Methods ............ 8-95
8-7.2 Range of Particle-size Distributions Suitable for Densification by
Vibrocompaction ....................................................................................... 8-96
8-7.3 Sand Densification Using Vibratory Rollers............................................... 8-97
8-7.4 Relative Density as a Function of Vibroflot Hole Spacings........................8-98
8-7.5 Allowable Bearing Pressure on Cohesionless Soil Layer Stabilized by
Vibroflotation ............................................................................................8-101
8-7.6 Soil Particle Sizes Suitable for Different Grout Types and Several
Concentrations and Viscosities Shown. ...................................................8-102
11-1 Frost and Permafrost in North America..................................................... 11-3
11-2 Ground Temperatures During Freezing Season in Limestone, Maine ...... 11-5
11-3 Ground Temperatures During Freezing Season in Fairbanks, Alaska .......11-6
11-4 Design Alternatives ..................................................................................11-12
11-5 Heave Force Tests……………………………………………………………. 11-16
12-1 Response Spectra for Vibration Limits…………………………………….. ...12-3
12-2 Response Curves for the Single-degree-of-Freedom System with Viscous
Damping.................................................................................................... 12-5
12-3 Six Modes of Vibration for a Foundation ................................................... 12-5
12-4 Equivalent Damping Ratio for Oscillation of Rigid Circular Footing on Elastic
Half-space................................................................................................. 12-6
12-5 Examples of Computations for Vertical and Rocking Motions................... 12-9
12-6 Coupled Rocking and Sliding Motion of Foundation.................................12-12
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Figure 6-1 Design Criteria for Cellular Cofferdams
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CHAPTER 1
INTRODUCTION
1-1 PURPOSE. This UFC presents guidance for selecting and designing
foundations for buildings and facilities of all types and associated features for buildings
such as earth embankments and slopes, retaining structures, and machinery
foundations. Foundations for hydraulic structures are not included; however,
foundations design methods for piers, wharves and waterfront structures are covered.
Foundation design differs considerably from design of other elements of a structure
because of the interaction between the structure and the supporting medium (soil and
rock). The soil and rock medium are highly variable as compared to steel and concrete
products above the soil; therefore, much attention is given to presenting subsurface
investigation methods to better determine the properties of the soil and rock. The
seismic aspects of foundation design are presented in detail.
1-2 SCOPE. Information contained in this UFC is directed toward construction
usually undertaken on military reservations, although it is sufficiently general to permit
its use on a wide variety of construction projects. Some of the references are directed
toward highway construction, but are also general enough to be applied to any
construction foundation items. Effort has been made to refer the user to as many non-
government standards as possible, when they appear to cover the topics as well as the
former manuals or provide new and innovative methods for the design of foundations on
soil and rock. Where there are no non-government criteria or insufficient coverage of
the topic in the non-government criteria, the existing government criteria from either the
U.S. Army Corps of Engineers or Naval Facilities Engineering Command publications
are either referenced or have been inserted totally in the document.
1-3 REFERENCES. Appendix A contains a list of references used in this
UFC. References are denoted as primary or secondary when mentioned in the
chapters. Primary references will cover the subject of the chapter in detail without the
aid of additional references. Secondary references may cover a portion of the subject
matter of a chapter in detail, but will need additional references to complete a design or
investigation. The non-government criteria primary references present both load factor,
used in the International Building Code, and safety factor design methods, whereas the
U.S Army Corps of Engineers Technical Manuals and Naval Facilities Engineering
Design Manuals present the classic design procedures using the traditional safety factor
design approaches.
1-4 GENERAL GUIDIANCE. These Geotechnical criteria are intended for a
graduate civil engineer who has had some Geotechnical engineering exposure in the
classroom and in the field of construction and engineering design for approximately
three years. The engineer should have access to a textbook in Geotechnical
engineering from the college attended and have access to the Internet to obtain the
references mentioned in the text.
1-4.1 Content Guidance. These Geotechnical engineering criteria have been
organized starting with a referenced textbook for background on shallow foundations,
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deep foundations, retaining structures, and slopes with settlement analysis covered in
each section. Specialty areas follow for excavation and stabilization for structures,
dewatering, and foundations in expansive soils, frost areas and seismic or vibration
environments.
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CHAPTER 2
SOILS AND GEOLOGY
2-1 INTRODUCTION
2-1.1 Purpose. The criteria presented in this UFC are the basic building blocks
of Geotechnical engineering. .
2-1.2 Scope. Apply criteria to all projects for the military services. Issues
concerning foundation investigations, and physical and strength properties and
classification of soils and rocks, and reporting on these are covered in the referenced
publications.
2-1.3 References.
• ASTM D2487, D 2488, and D 5878
• Soil Sampling, Technical Engineering and Design Guides
• Geophysical Exploration for Engineering and Environmental
Investigations, Technical Engineering and Design
• Fundamentals of Geotechnical Engineering
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Figure 8-1.2
Skeleton Shoring
Figure 8-1.3
Close (Tight) Sheeting
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FIGURE 8-1.10
Guideline for Assessing Potential for Damage Induced by Blasting Vibration to
Residential Structure Founded on Dense Soil or Rock
FIGURE 8-1.11
Guide for Predicting Human Response to Vibrations and Blasting Effects
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Table 3-1 Foundation Possibilities for Different Subsoil Conditions
Foundation Possibilities
Subsoil Conditions Light, Flexible Structure Heavy, Rigid Structure
Deep Compact or Stiff Deposit Footing Foundations Footing Foundations or
Shallow Mat
Deep Compressible Strata Footing Foundations on
Compacted Granular Zonea
, or
Shallow Mata
, or
Friction Piles
Deep Mat with Possible Rigid
Construction in Basementa
, or
Long Piles or Caissons to By-
Pass, or
Friction Piles
Soft or Loose Strata Overlying
Firm Strata
Bearing Piles or Piers, or
Footing Foundations on
Compacted Granular Zonea
, or
Shallow Mata
Bearing Piles or Piers, or
Deep Mat
Compact or Stiff Layer
Overlying Soft Deposit
Footing Foundationsa
, or
Shallow Mata
Deep Mat (Floating), or
Long Piles or Caissons to By-
pass Soft Deposit
Alternating Soft and Stiff
Layers
Footing Foundationsa
, or
Shallow Mata
Deep Mat, or
Piles or Caissons to
Underlying Firm Stratum to
provide Satisfactory
Foundation
a
Consider possible advantages of site pre-loading, with or without vertical drains, to accelerate
consolidation.
(Courtesy L.J. Goodman and R.H. Kerol, Theory and Practice of Foundation Engineering, 1968, P.312
Reprinted by permission MacMillan Company, Inc., New York)
3-3

Table 8-1.5
Relative Desirability of Soils as Compacted Fill
Relative Desirability for Various Uses
Rolled Earth Fill
Dams
Canal Sections Foundations Roadways
Soil Type
Fills
Group
Symbol
ErosionResistance
CompactedEarth
L
Homogeneous
Embankment
Core
Shell
ining
H
SeepageNot
Important
FrostHeave
NotPossible
Surfacing
Seepage
Important
Frosteave
Possible
GW Well graded gravels,
gravel-sand mixture, little
or fines
- - 1 1 - - 1 1 1 3
GF Poorly graded gravels,
gravel-sand mixture, little
or no fines
- - 2 2 - - 3 3 3 -
GM Silty gravels, poorly graded
gravel-sand-silt mixtures
2 4 - 4 4 1 4 4 9 5
GC Clayey gravels, poorly
graded gravel-sand-clay
mixtures
1 1 - 3 1 2 6 5 5 1
SW Well graded sands, gravel
like sands, little or no fines
- - 3 if
gravelly
6 - - 2 2 2 4
SP Poorly graded sands,
gravel like sands, little or
no fines
- - 4 if
gravelly
7 if
gravelly
- - 5 6 4 -
SM Silty sands, poorly graded
sand-silt mixtures
4 - 8 if
gravelly
5
erosi
on
critic
al
3 7 6 10 6
SC Clay like sands, poorly
graded sand-clay mixtures
3 2 - 5 2 4 8 7 6 2
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Table 8-1.6
Clay Dispersion Potential
*Percent Dispersion Dispersive Tendency
Over 40 Highly Dispersive (do not use)
15 to 40 Moderately Dispersive
0 to 15 Resistant to Dispersion
*The ratio between the fraction finer than 0.005 mm in a soil-water
suspension that has been subjected to a minimum of mechanical
agitation, and the total fraction finer than 0.005 mm determined
from a regular hydrometer test x 100.
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• American Society of Civil Engineers, Bearing Capacity of Soils,
Technical Engineering and Design
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CHAPTER 5
DEEP FOUNDATIONS
5-1 INTRODUCTION
5-1.1 Purpose. The criteria presented in this UFC are to be used by the
engineer to develop the types, lengths, diameters or horizontal dimensions, materials
and installation methods of deep foundations. Deep foundations are those that receive
some or all of their support from soil strata at a depth where the Depth of bearing/Base
width of footing ratio is greater than 5. The materials for deep foundations may be
concrete, steel, timber, aggregates, soils and combinations of these materials including
mixed in placed soils with Portland cement, limes and fly ashes. There are many
installation methods, and some examples are driving with hammers or rams, screw type
installations, drilled installations, deep mixing, deep compaction and grout injection.
There are new developments in this field everyday. It is important to seek the latest
guidance from the references and from the geotechnical engineering community. ASCE
Geotechnical Institute and the Deep Foundations Institute are the main sources of
information for developments in deep foundations.
of determining the most economical deep foundation, settlement potential, bearing
capacity and size of the deep foundations is presented in detail.
5-1.3 Related Criteria. Reference Chapter 10, "Foundations in Expansive
Soils" and Chapter 11, "Foundations in Areas of Significant Frost Penetration" when
designing deep foundations when either of these factors, expansive soil or significant
frost penetration, are present for a particular site.
5-1.4 References. These present load factor and safety factor type designs
and should be used as a unit.
• Design of Pile Foundations, Technical Engineering and Design
Guides
• American Society Of Civil Engineers/Geo-Institute, 20-96, Standard
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Guidelines for the Design and Installation of Pile Foundation
• 2000 International Building Code (IBC 2000)
Chapter 18, http://www.icbo.org/
• Design of Sheet Pile Walls, Technical Engineering and Design
Guides
• Deep Foundations Institute,
Auger CIP Piles Manual
Inspectors Guide to Augered CIP Piles
Drilled Shaft Inspector’s Manual
Lexicon of Foundation Terms in Five Languages
Driven Foundation Piling (Catalog 1998)
Dynamic Monitoring and Analysis
Interpretation & Analysis fo the Static Loading Test
Guidelines for Static Design
Testing of Pile Driving Cushion Material
Soil Nailing Design & Applications
Inspector's Manual for Pile Foundations
• Pile Buck, Inc. http://www.pilebuck.com/
3800 SW Boat Ramp Road, Palm City, Florida 34990
• ADSC: The International Association of Foundation Drilliing, Drilled
Shafts
Drilled Shafts - Axial Loads Drilled Shafts – Testing, Uplift
Drilled Shafts - Clay Drilled Shafts – Uplift
Drilled Shafts – Concrete Earth Retention
Drilled Shafts - Design Drilled Shafts – Testing, Uplift
Drilled Shafts – Design, General
Drilled Shafts – General
Drilled Shafts – Non-Destructive
Testing
Drilled Shafts – Rock
Drilled Shafts - Sand
Drilled Shafts – Shale, Slurry
Drilled Shafts – Slurry
Drilled Shafts – Soils
Drilled Shafts – Specifications
Drilled Shafts – Testing
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CHAPTER 6
RETAINING WALLS AND CELLULAR COFFERDAMS
6-1 INTRODUCTION
engineer to develop the type, dimensions, and materials for building retaining walls
under waterfront conditions to mountainous terrain. The materials may be concrete,
metals, timber, soils, geotextiles and/or combinations of these materials. A special
reference and paragraphs are added here for cellular cofferdams. Cellular cofferdams
are very similar to retaining walls but require special design attention.
6-1.2 Scope. Apply the Geotechnical criteria to all projects for the military
services. The methods of determining settlement potential, bearing capacity, earth
pressures, and the size of the retaining walls is presented in detail. The criteria for
designing retaining structures or walls that include gravity, concrete, steel, tied and
braced bulkheads and cofferdams is presented in easily understood formats with real
life examples to guide the engineer.
6-1.3 Related Criteria. Chapters 7, Slope Stability Analysis, Chapter 8,
Excavation, Fill, Backfill, and Soil Stabilization for Structures, Chapter 9, De-watering
and Groundwater Control, Chapter 10, Foundation in Expansive Soils, Chapter 11,
Foundations in Areas of Significant Frost Penetration and Chapter 12, and Foundations
for Vibrating Equipment and seismic loadings should be consulted for conditions that
may effect the design of the retaining wall systems.
6-1.4 Cellular Cofferdams. Double-walled or cellular cofferdams consist of a
line of circular cells connected by smaller arcs, parallel semi-circular walls connected by
straight diaphragms or a succession of cloverleaf cells (see Figure 6-1). For analysis,
these configurations are transformed into equivalent parallel wall cofferdams of width B.
6-1.4.1 Analysis. Stability depends on the ratio of width to height, the resistance
of an inboard berm, if any, and type and drainage of cell fill materials.
6-1.4.1.1 Exterior Pressures. Usually active and passive pressures act on exterior
faces of the sheeting. However, there are exceptions. These are illustrated in Figure
6.1.
6-1.4.1.2 Stability Requirements. A cell must be stable against sliding on its base,
shear failure between sheeting and cell fill, and shear failure on the centerline of the
cell. It must also resist bursting pressures through interlock tension. These failures are
influenced by foundation type. See Figure 6-1 for design criteria for cofferdams with,
and without, berms, on rock, and on fine-grained or coarse-grained soil.
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• Sand base. For cell walls on sand, penetration of sheeting must be sufficient
to avoid piping at the interior toe of the wall and to prevent pullout of outboard
sheeting.
• Clay base. For cofferdams on clay, penetration of the outboard sheeting is
usually controlled by the pullout requirement; piping is not critical.
• Bearing capacity. For cofferdams in either clay or sand, check the bearing
capacity at the inboard toe by methods for shallow foundations.
6-1.4.1.3 Cell Deformations. The maximum bulging of cells occurs at
approximately ¼ the height above the cofferdam base. The cells tilt 0.02 to 0.03
radians due to the difference in lateral loads on the outboard and inboard faces.
Deflections under the lateral overturning loads are a function of the dimensions, the
foundations support, and the properties of the cell fill.
6-1.4.2 Cell Fill. Clean, coarse-grained, free-draining soils are preferred for cell
fill. They may be placed hydraulically or dumped through water without any requirement
for compaction or special drainage.
• Materials. Clean, granular fill materials should be used in large and critical
cells. Every alternative should be studied before accepting fine-grained
backfill as fine-grained soils produce high bursting pressures and minimal cell
rigidity. Their use may require the addition of interior berms, increased cell
width, or consolidation (by sand drains or pumping). All soft material trapped
within the cells must be removed before filling.
• Drainage. Install weep holes on inboard sheeting to the cell fill. For critical
cells, and/ or those with marginal fill material, wellpoints, or wells between
cells have been used to increase cell stability.
• Corrosion retardation. When cofferdams are used in permanent structures,
especially in locations exposed to brackish water or seawater, sever corrosion
occurs from the top of the splash zone to a point just below mean low-water
level. Use a protective coating, corrosion resistant steel and/ or cathodic
protection in those areas.
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3 (TEMPORARY WALL)
3.5 (PERMANENT WALL)
1.5 (TEMPORARY WALL)
2.0 (PERMANENT WALL)
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6-1.5 References. Present load factor and safety factor type designs and
should be used a unit.
• Retaining and Flood Walls, Technical Engineering and Design guides
• Design of Sheet Pile Walls, Technical Engineering and Design
Guides
• “Sheet Pile Tensions in Cellular Structures”
• Foundations, Design and Practice
• “Design, Construction and Performance of Cellular Cofferdams”
• “Field Study of Cellular Cofferdams”
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CHAPTER 7
SLOPE STABILITY ANALYSIS
7-1 INTRODUCTION
engineer to develop dimensions and details for existing or new slopes, and for
predicting their safety and reliability.
to analyze the stability and reliability, dimensions, and safety of natural slopes and
constructed earth embankments are present in the references cited. Slope failures can
be rapid and progressive when overstressed by external loads or a reduction of shear
strength of the soil material within the slope. The factor of safety is simply the ratio of
the force resisting failure to the sum of the forces causing rupture along the defined slip
surface. The criteria give the engineer methods of determining these forces.
7-1.3 Related Criteria. See Chapter 4, "Shallow Foundations", and Chapter 8,
"Excavation, Fill, Backfill, and Soil Stabilization for Structures" for additional criteria that
may apply to slope stability.
7-1.4 References. These present the load factor and safety factor methods of
design.
• UFC 3-220-10N,
• Engineering Manual for Slope Stability Studies.
• 2000 International Building Code (IBC 2000)
Chapter 18, http://www.icbo.org/
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CHAPTER 8
EXCAVATIONS, FILL, BACKFILL, AND SOIL STABILIZATION FOR STRUCTURES
8-1 EXCAVATIONS
8-1.1 Introduction and Scope
This chapter covers the methods of evaluating the stability of shallow and deep
excavations. There are two basic types of excavations:
• “open excavations” where stability is achieved by providing stable side
slopes
• “braced excavations” where vertical or sloped sides are maintained
with protective structural systems that can be restrained laterally by
internal or external structural elements. Guidance on performance
monitoring is given in Logging the Mechanical Character of Rocks,
Chapter 2.
8-1.1.1 Methodology. In selecting and designing the excavation system, the
primary controlling factors will include:
• soil type and soil strength parameters
• groundwater conditions
• slope protection
• side and bottom stability
• vertical and lateral movements of adjacent areas, and effects on
existing structures
8-1.1.2 Related Criteria. For additional criteria on excavations, see UFC 3-220-
05, Dewatering and Groundwater Control.
8-1.2 Open Cuts
8-1.2.1 Sloped Cuts. Depth and slope of an excavation, and groundwater
conditions control the overall stability and movements of open excavations. In granular
soils, instability usually does not extend significantly below the excavation, provided
seepage forces are controlled. In rock, depths and slopes of excavation, particular joint
patterns, in situ stresses, and groundwater conditions control stability. In cohesive soils,
instability typically involves side slopes but may also include materials well below the
base of the excavation. Instability below the base of excavation, often referred to as
bottom heave, is affected by soil type and strength, depth of cut, side slope and/or berm
geometry, groundwater conditions, and construction procedures. Methods for
controlling bottom heave are given in UFC 3-220-10N.
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Methods described in UFC 3-220-10N may be used to evaluate the stability of open
excavations in soils where behavior of such soils can be reasonably determined by field
investigation, laboratory testing, and analysis. In certain geologic formations (stiff clays,
shales, sensitive clays, clay tills, etc.) stability is controlled by construction procedures,
side effects during and after excavation and inherent geologic planes of weaknesses -
Table 8-1.1 (modified from Effects of Construction on Geotechnical Engineering, by
Clough and Davidson) presents a summary of the primary factors controlling excavation
slopes in some problem soils. Table 8-1.2 (modified from UFC 3-220-10N) summarizes
measures that can be used for excavation protection for both conventional and problem
soils.
8-1.2.2 Vertical Cuts. Many cuts in clays will stand with vertical slopes for a
period of time before failure occurs. However, changes in the shear strength of the clay
with time and stress release resulting from the excavation can lead to progressive
deterioration in stability. This process can be rapid in stiff, highly fissured clays, but
relatively slow in softer clays. (See UFC 3-220-10N for critical heights for vertical cuts in
cohesive soils.) For cuts in hard unweathered rock, stability is mostly controlled by
strength along bedding planes, groundwater condition, and other factors (see UFC 3-
220-10N, and Stability of Steep Slopes on Hard Unweathered Rock, by Terzaghi for
detailed discussion on the effects of rock discontinuities). Cuts in rock can stand
vertical without bolting or anchoring depending on rock quality and joint pattern.
8-1.3 Trenching
8-1.3.1 Site Exploration. Individual trenching projects frequently extend over
long distances. An exploration program should be performed to define the soil and
groundwater conditions over the full extent of the project, so that the design of the
shoring system can be adjusted to satisfy the varying site conditions.
8-1.3.2 Trench Stability. Principal factors influencing trench stability are the
lateral earth pressures on the wall support system, bottom heave, and the pressure and
erosive effects of infiltrating groundwater (see Chapter 6 and UFC 3-220-10N). External
factors that influence trench stability include:
• Surface Surcharge. The application of any additional load between the
edge of the excavation and the intersection of the ground surface with
the possible failure plane must be considered in the stability analyses
for the excavation.
• The effects of vibrating machinery, blasting or other dynamic loads in
the vicinity of the excavation must be considered. The effects of
vibrations are cumulative over periods of time and can be particularly
dangerous in brittle materials such as clayey sand or gravel.
• Ground Water Seepage. Improperly dewatered trenches in granular
soils can result in quick conditions and a complete loss of soil strength
or bottom heave. (See UFC 3-220-10N.)
• Surface Water Flow. This can result in increased loads on the wall
support system and reduction of the shear strength of the soil. Site
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In situ material permeability characteristics for the design of construction
excavation dewatering systems can also be approximated from laboratory tests on
representative undisturbed samples. Laboratory permeability tests on undisturbed samples
are less expensive than in situ pumping tests performed in the field; however, laboratory tests
are less accurate in predicting flow characteristics.
8-3.3.2.2.6 Slake Durability of Shales. Some clay shales tend to slake when exposed to
air and water and must be protected immediately after they are exposed. The extent of slaking
also governs the manner in which they are treated as a backfill material (paragraph 8-3.3.3.3).
Slaking characteristics can be evaluated by laboratory jar-slake tests or slake-durability tests.
The jar-slake test is qualitative with six descriptive degrees of slaking determined
from visual observation of oven dried samples soaked in tap water for as long as 24 hours.
The jar-slake test is not a standardized test. One version of the jar-slake test is discussed in
FHWA-RD-78-141. Six suggested values of the jar-slake index IJ are listed below:
Shales with IJ values of 1 to 3 should be protected when occurring in excavated slopes and
compacted as soil if used for backfill.
The slake-durability test is a standardized test that gives a quantitative
description in percent by weight of material remaining intact at the conclusion of the test.
Details of the test are presented in FHWA-RD-78-141.
8-3.3.2.2.7 Dynamic Tests for Special Projects. Dynamic tests for special projects
The dynamic analysis of projects subject to seismic or blast induced loading conditions
requires special dynamic tests on both in situ and backfill materials. Tests required for
dynamic analysis include: cyclic triaxial tests; in situ density measurements; and tests to
determine shear wave velocities, shear modulus, and damping (ER 1110-2-1806).
8-3.3.2.2.8 In-situ Water Content. The in situ water content, including any seasonal
variation, must be determined prior to construction for materials selected for use as backfill.
Natural in situ water contents will determine the need for wetting or drying the backfill material
before placement to obtain near optimum water contents for placement and compaction.
ASTM D 2216 discusses the test method for determining water content.
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8-3.4 Selection of Backfill Materials. Selection of backfill materials should be based
upon the engineering properties and compaction characteristics of the materials available.
The results of the field exploration and laboratory test programs should provide adequate
information for this purpose. The materials may come from required excavation, adjacent
borrow pits, or commercial sources. In selecting materials to be used, first consideration
should be given to the maximum use of materials from required excavation. If the excavated
materials are deficient in quality or quantity, other sources should be considered. Common
backfill having the desired properties may be found in borrow areas convenient to the site, but
it may be necessary to obtain select backfill materials having particular gradation
requirements, such as filter sands and gravels and pipe or conduit bedding materials from
commercial sources.
8-3.4.1 Primary Considerations. Primary considerations for borrow material sources
are suitability and quantity. Accessibility and proximity of the borrow area to the jobsite should
also be considered. The water contents of the borrow area material should be determined
seasonally, and a source of water should be located if the natural water contents are
considerably less than the required placement water content. If several sources of suitable
backfill are available, other factors to be considered in selecting the borrow materials are ease
of loading and spreading and the means for adding or reducing water. The need for
separating or mixing soil strata from excavation or borrow sources should be considered if
necessary to provide reasonably uniform engineering properties throughout the compacted
backfill.
8-3.4.2 Compaction Characteristics. If compaction characteristics of the major portion
of the backfill are relatively uniform, problems of controlling placement of backfill will be
significantly reduced since the inspector will be able to develop more rapidly the ability to
recognize the adequacy of the compaction procedures. In addition, the frequency of testing for
compaction control could be reduced. When available backfill materials are unusual, test
sections of compacted backfill are sometimes justified to develop placement procedures and to
determine the engineering characteristics to be expected in field-compacted materials.
8-3.4.3 Workability. An important factor in choosing backfill materials is the workability
or ease with which the soil can be placed and compacted. Material characteristics that effect
workability include: the ease of adjusting water contents in the field by wetting or aeration; the
sensitivity to the compaction water content with respect to optimum; and the amount of
compaction effort required to achieve specified densities.
8-3.4.4 Types of Backfill Material. A discussion of the many types of backfill and their
compaction characteristics is beyond the scope of this manual since soil types will vary on
each project. However, the compaction characteristics of several rather broad categories of
backfill (Table 8-3.1) are discussed briefly.
8-3.4.4.1 Coarse-Grained Soils. Coarse-grained soils include gravelly and sandy soils
and range from clayey sands (SC) through the well-graded gravels of gravelsand mixtures
(GW) with little or no fines (table 8-3.1). They will exhibit slight to no plasticity. All of the well-
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graded soils falling in this category have fairly good compaction characteristics and when
adequately compacted provide good backfill and foundation support.
One difficulty that might arise with soils in this category would be in obtaining
good compaction of the poorly graded sands and gravels. These poorly graded materials may
require saturation with downward drainage and compaction with greater compaction effort to
achieve sufficiently high densities. Also, close control of water content is required where silt is
present in substantial amounts. Coarse-grained materials compacted to a low relative density
are susceptible upon saturation to liquefaction under dynamic loads.
For sands and gravelly sands with little or no fines, good compaction can be
achieved in either the air-dried or saturated condition. Downward drainage is required to
maintain seepage forces in a downward direction if saturation is used to aid in compaction.
Consideration may be given to the economy of adding cement to stabilize moist clean sands
that are particularly difficult to compact in narrow confined areas. However, the addition of
cement may produce zones with greater rigidity than untreated adjacent backfill and form "hard
spots" resulting in non-uniform stresses and deformations in the structure.
Cohesionless materials are well suited for placement in confined areas adjacent
to and around structures where heavy equipment is not permitted and beneath and around
irregularly shaped structures, such as tunnels, culverts, utilities, and tanks. Clean, granular,
well-graded materials having a maximum size of 1 inch with 95 percent passing the 4.75 mm
(No. 4) sieve and 5 percent or less passing the 75 Micron (No. 200) sieve are excellent for use
in these zones. However, a danger exists of creating zones where seepage water may
accumulate and saturate adjacent cohesive soils resulting in undesirable consolidation or
swelling. In such cases, provisions for draining the granular backfill, sealing the surface, and
draining surface water away from the structure are necessary.
8-3.4.4.2 Fine-Grained Soils of Low to Medium Plasticity. Inorganic clays (CL) of low
to medium plasticity (gravelly, sandy, or silty clays and lean clays) and inorganic silts and very
fine sands (ML) of low plasticity (silty or clayey fine sands and clayey silts) are included in this
category. The inorganic clays are relatively impervious and can be compacted fairly easily
with heavy compaction equipment to provide a good stable backfill. Soils in the CL group can
be compacted in confined areas to a fairly high degree of compaction with proper water
content and lift thickness control. The clayey sands of the SC group and clayey silts of the ML
group can be compacted to fairly high densities, but close control of water content is essential
and sometimes critical, particularly on the wet side of optimum water content. Some ML soils, if
compacted on the dry side of optimum, may lose considerable strength upon saturation after
compaction. Considerable settlement may occur. Caution must therefore be exercised in the
use of such soils as backfill, particularly below the groundwater level. Also, saturated ML soils
are likely to be highly susceptible to liquefaction when dynamically loaded. Where such soils
are used as backfill in seismic prone areas, laboratory tests should be conducted to determine
their liquefaction potential.
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8-1.3.3 Support Systems. Excavation support systems commonly used are as
follows:
• Trench Shield. A rigid prefabricated steel unit used in lieu of shoring,
which extends from the bottom of the excavation to within a few feet of the
top of the cut. Pipes are laid within the shield, which is pulled ahead, as
trenching proceeds, as illustrated in Figure 8-1.1 (from “Cave-In!” by
Petersen). Typically, this system is useful in loose granular or soft
cohesive soils where excavation depth does not exceed 3.5 m (12 ft).
Special shields have been used to depths of 9 m (30 ft).
• Trench Timber Shoring. Table 8-1.3 illustrates the Occupational Safety
and Health Act's minimum requirements for trench shoring. Braces and
shoring of trench are carried along with the excavation. Braces and
diagonal shores of timber should not be subjected to compressive
stresses in excess of:
S = 1300 - 20 L/D
where:
L = unsupported length (mm or inches)
D = least side of the timber (mm or inches)
S = allowable compressive stress in kilograms per square cm
(pounds per square inch) of cross section
Maximum Ratio L/D = 50
* Note: L/D units need to be consistent
• Skeleton Shoring. Used in soils where cave-ins are expected. Applicable
to most soils to depth up to 9.1 m (20 ft). See Figure 8-1.2 (from “Cave-
In”) for illustration and guidance for skeleton shoring. Structural
components should be designed to safely withstand earth pressures.
• Close (Tight) Sheeting. Used in granular or other running soils, compared
to skeleton shoring, it is applicable to greater depths. See illustration in
Figure 8-1.3 (from “Cave-In”)
• Box Shoring. Applicable to trenching in any soil. Depth limited by
structural strength and size of timber. Usually limited to 18.2 m (40 ft).
See illustration in Figure 8-1.4 (from “Cave-In”)
• Telescopic Shoring. Used for excessively deep trenches. See illustration
in Figure 8-1.5 (“Cave-In”).
• Steel Sheeting and Bracing. Steel sheeting and bracing can be used in
lieu of timber shoring. Structural members should safely withstand water
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8-7
and lateral earth pressures. Steel sheeting with timber wales and struts
has also been used.
FIGURE 8-1.1
Sliding Trench Shield

Table 8-1.3
OSHA Requirements (Minimum) for Trench Shoring
Size and Spacing of Members
Uprights Stringers Cross Braces1
Width of Trench (feet)
Maximum Spacing
Depth of
Trench
Kind or Condition
of Earth
Minimum
Dimension
Maximum
Spacing
Minimum
Dimension
Maximum
Spacing
Up to 3 4 to 6 7 to 9 10 to 12 13 to 15
Vertical Horizontal
Feet Inches Feet Inches Feet Inches Inches Inches. Inches Inches Feet Feet
5 to 10 Hard, compact 3 x 4 or 2 x 6 6 -- -- 2 x 6 4 x 4 4 x 6 6 x 5 6 x 8 4 6
Likely to crack 3 x 4 or 2 x 6 3 4 x 6 4 2 x 6 4 x 4 4 x 6 6 x 6 6 x 8 4 6
3 x 4 or 2 x 6 4 x 6 4 4 x 4 4 x 6 6 x 6 6 x 8 8 x 8 4 6Soft, sandy, or filled Close
Sheeting
3 x 4 or 2 x 6 6 x 8 4 4 x 4 4 x 6 6 x 6 6 x 8 8 x 8 4 6Hydrostatic
Pressure
Close
Sheeting
11 to 15 Hard 3 x 4 or 2 x 6 4 4 x 6 4 4 x 4 4 x 6 6 x 6 6 x 8 8 x 8 4 6
Likely to crack 3 x 4 or 2 x 6 2 4 x 6 4 4 x 4 4 x 6 6 x 6 6 x 8 8 x 8 6
3 x 4 or 2 x 6 4 x 6 4 4 x 6 6 x 6 6 x 8 8 x 8 8 x 10 4 6Soft, sandy or
Filled
Close
Sheeting
3 x 6 8 x 10 4 4 x 6 6 x 6 6 x 8 8 x 8 8 x 10 4 6Hydrostatic
Pressure
Close
Sheeting
16 to 20 3 x 6 4 x 12 4 4 x 12 6 x 8 8 x 8 8 x 10 10 x 10 4 6All kinds or
Conditions
Close
Sheeting
Over 20 3 x 6 6 x 8 4 4 x 12 8 x 8 8 x 10 10 x 10 10 x 12 4All kinds or
Conditions
Close
Sheeting
1
Trench jacks may be used in lieu of, or in combination with, cross braces. Where desirable, steel sheet piling and bracing of equal strength
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Figure 8-1.4
Box Shoring
Figure 8-1.5
Telescopic Shoring
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8-1.4 ROCK EXCAVATION
8-1.4.1 Preliminary Considerations. The primary objective is to conduct work in
such a manner that a stable excavation will be maintained and that rock outside the
excavation prism will not be adversely disturbed. Rock excavation planning must be
based on detailed geological data at the site. To the extent possible, structures to be
constructed in rock should be oriented favorably with the geological setting. For
example, tunnels should be aligned with axis perpendicular to the strike of faults or
major fractures. Downslope dip of discontinuities into an open cut should be avoided.
In general, factors that must be considered in planning, designing and constructing a
rock excavation are as follows:
• Presence of strike, dip of faults, folds, fractures, and other discontinuities
• In situ stresses
• Groundwater conditions
• Nature of material filling joints
• Depth and slope of cut
• Stresses and direction of potential sliding; surfaces
• Dynamic loading, if any
• Design life of cut as compared to weathering or deterioration rate of rock face
• Rippability and/or the need for blasting
• Effect of excavation and/or blasting on adjacent structures
The influence of most of these factors on excavations in rock is similar to that of
excavations in soil; see UFC 3-220-10N.
FIGURE 8-1.6
General Guidance for Underpinning
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8-1.4.2 Rippability. Excavation ease or rippablility can be assessed
approximately from field observation in similar materials or by using seismic velocity,
fracture spacing, or point load strength index. Figure 8-1.7 (from Handbook of Ripping,
by Caterpillar Tractor Co.) shows an example of charts for heavy-duty ripper
performance (ripper mounted on tracked bulldozer) as related to seismic wave velocity.
Charts similar to Figure 8-1.8 are available from various equipment manufacturers.
Figure 8-1.8 is for guidance and restricted in applicability to large tractors heavier than
50 tons with engine horsepower greater than 350 Hp. Ripper performance is also
related to configuration of ripper teeth, equipment condition and size, and fracture
orientation.
Another technique of relating physical properties of rock to excavation ease is shown in
Figure 8-1.9, (from Logging the Mechanical Character of Rock, by Franklin, et al.)
Where fracture frequency (or spacing) is plotted against the point load strength index
corrected to a reference diameter of 50 mm (see The Point-Load Strength Test, by
Broch and Franklin).
A third and useful technique is exploration trenching in which the depth of unrippable
rock can be established by digging test trenches in rock using rippers (or other
excavation equipment) anticipated to be used for the project. The size and shape of the
area to be excavated is a significant factor in determining the need for blasting, or the
equipment needed to remove the rock.
8-1.4.3 Blasting. Of major concern is the influence of the blasting on adjacent
structures. The maximum particle velocity (the longitudinal velocity of a particle in the
direction of the wave that is generated by the blast) is accepted as a criterion for
evaluating the potential for structural damage induced by blasting vibration. The critical
level of the particle velocity depends on the frequency characteristics of the structure,
frequency of ground and rock motion, nature of the overburden and capability of the
structure to withstand dynamic stress. Figure 8-1.9 can be used for estimating the
maximum particle velocity, which can then be used in Figure 8-1.10 (from Blasting
Vibrations and Their Effects on Structures, by Bureau of Mines) to estimate potential
damage to residential structures. Guidance for human response to blasting vibrations is
given in Figure 8-1.11 (from Engineering of Rock Blasting on Civil Protects, by
Hendron).
Once it has been determined that blasting is required, a pre-blasting survey should be
performed. At a minimum, this should include:
• Examination of the site
• Detailed examination and, perhaps, photographic records of adjacent
structures
• Establishment of horizontal and vertical survey control points
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• Another method is to place clean, granular bedding material with
pneumatic concrete equipment under the haunches of pipes, tunnels, and
tanks. The material is placed wet and should have an in-place water
content of approximately 15 to 18 percent. A nozzle pressure of 40
pounds per square inch is required to obtain proper density. Considerable
rebound of material (as much as 25 percent by volume when placed with
the hose nozzle pointed vertically downward and 50 percent with the
nozzle pointed horizontally) occurs at this pressure. Rebound is the
material that bounces off the surface and falls back in a loose state.
However, the method is very satisfactory if all rebound material is
removed. The material can be effectively removed from the backfill by
dragging the surface in the area where material is being placed with a
flat-end shovel. Two or three men will be needed for each gunite hose
operated.
• For structures and pipes that can tolerate little or no settlement, lean
grouts containing granular material and various cementing agents, such
as portland cement or fly ash, can be used. This grout may be placed by
either method discussed above. However, grouts may develop hard spots
(particularly where the sluice method is used that could cause segregation
of the granular material and the cementing agent), which could generate
stress concentrations in rigid structures such as concrete pipes. Stress
concentrations may be severe enough to cause structural distress. If lean
grouts are used as backfill around a rigid structure, the structure must be
designed to withstand any additional stress generated by possible hard
spots.
8-5.4 Installation of Instruments. Installation of instrumentation devices
should be supervised, if not actually done, by experienced personnel from Contracting
Officer’s Organization or by firms that specialize in instrumentation installation. The
resident engineer staff must be familiar with the planned locations of all instruments and
necessary apparatus or structures (such as trenches and terminal houses) so that
necessary arrangements and a schedule for installation can be made with the
contractor and with the office or firm that will install the devices. Inspectors should
inspect any instrumentation furnished and installed by the contractor. Records must be
made of the exact locations and procedures used for installation and initial
observations. Inspectors should ensure that necessary extensions are added for the
apparatus (such as lead lines and piezometer tubes) installed within the backfill as the
backfill is constructed to higher elevations. Care must be used in placing and
compacting backfill around instruments that are installed within or through backfill.
Where necessary to prevent damage to instruments, backfill must be placed manually
and compacted with small compaction equipment such as rammers or vibratory plates.
8-5.5 Post-construction Distress. Good backfill construction practices and
control will minimize the potential for postconstruction distress. Nevertheless, the
possibility of distress occurring is real, and measures must be taken to correct any
problems before they become so critical as to cause functional problems with the
facility. Therefore, early detection of distress is essential. Some early signs of possible
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connected by prima cord, or simply the prima cord alone, are strung the full depth of the
hole. Each hole is detonated in succession, and the resulting large diameter holes
formed by lateral displacement are backfilled. A sluiced-in cohesionless backfill will
densify under the action of vibrations from subsequent blasts. Finer grained backfills
can be densified by tamping.
8-7.2.2 Vibrating Probe (Terraprobe). A 30-in-outside-diameter, open-ended
pipe pile with 9.5 mm (3/8-in) wall thickness is suspended from a vibratory pile driver
operating at 15 Hz. A probe length from 3.05 to 4.57 m (10 to 15 ft) greater than the soil
depth to be stabilized is used. Vibrations of 9.5 mm to 25.4 mm (3/8 to 1 in) amplitude
are applied in a vertical mode. Probes are made at a spacing of between 0.91 and 3.05
m (3 to 10 ft). After the soil sinks to the desired depth, the probe is held for 30 to 60
seconds before extraction. The total time required per probe is typically 2 ½, to 4
minutes. Effective treatment has been accomplished at depths of 3.66 to 18.29 m (12
to 60 ft). Areas in the range of 376 to 585 m2
(450 to 700 sq yd) may be treated per
machine per 8 hour shift.
Test sections about 9.1 to 18.3 m (30 to 60 ft) on a side are desirable to evaluate the
effectiveness and required probe spacing. The grain-size range of treated soil should
fall within limits shown in Figure 16-2. A square pattern is often used, with a fifth probe
at the center of each square giving more effective increased densification than a
reduced spacing. Saturated soil conditions are necessary as underlying soft clay layers
may dampen vibrations.
8-7.2.3 Vibratory Rollers. Where cohesionless deposits are of limited thickness,
e.g., less than 2 m (6 ft), or where cohesionless fills are being placed, vibratory rollers
are likely to be the beat and most economical means for achieving high density and
strength. Use with flooding where a source of water is available. The effective depth of
densification may be 2 m (6 ft) or more for heaviest vibratory rollers or a fill placed in
successive lifts, a density-depth distribution similar to that in Figure 8-7.3 results. It is
essential that the lift thickness, soil type, and roller type be matched. Properly matched
systems can yield compacted layers at a relative density of 85 to 90 percent or more.
8-7.3 Vibrodisplacement Compaction. The methods in this group are similar
to those described in the preceding section except that the vibrations are supplemented
by active displacement of the soil and, in the case of vibroflotation and compaction
piles, by backfilling the zones from which the soil has been displaced.
8-7.3.1 Compaction Piles. Partly saturated or freely draining soils can be
effectively densified and strengthened by this method, which involves driving
displacement piles at close spacings, usually 1 to 2 m (3 to 6 ft) on centers. One
effective procedure is to cap temporarily the end of a pipe pile (e.g., by a detachable
plate) and drive it to the desired depth, which may be up to 18 m (60 ft). Either an
impact hammer or a vibratory driver can be used. Sand or other backfill material is
introduced in lifts with each lift compacted concurrently with withdrawal of the pipe pile.
In this way, not only is the backfill compacted, but the compacted column has also
expanded laterally below the pipe tip forming a caisson pile.
8-7.3.2 Heavy Tamping (Dynamic Consolidation). Repeated impacts of a very
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heavy weight (up to356 kN (80 kips)) dropped from a height of 15 to 40 m (50 to 130 ft)
are applied to points spaced 4.5 to 9.0 m (15 to 30 ft) apart over the area to be
densified. In the case of cohesionless soils, the impact energy causes liquefaction
followed by settlement as water drains. Radial fissures that form around the impact
points, in some soils, facilitate drainage. The method has been used successfully to
treat soils both above and below the water table.
The product of tamper mass and height of fall should exceed the square of the
thickness of layer to be densified. A total tamping energy of 2 to 3 blows per square
meter or square yard is used. Increased efficiency is obtained if the impact velocity
exceeds the wave velocity in the liquefying soil. One crane and tamper can treat from
293 to 627 m2
(350 to 750 sq yd) per day. Economical use of the method in sands
requires a minimum treatment area of 2671 m2
(7500 sq yd). Relative densities of 70 to
90 percent are obtained. Bearing capacity increases of 200 to 400 percent are usual for
sands and marls, with a corresponding increase in deformation modulus. The cost is
reported as low as one-fourth to one-third that of vibroflotation.
Because of the high-amplitude, low-frequency vibrations (2-12 Rz), minimum distances
should be maintained from adjacent facilities as follows:
Piles or bridge abutment 4.6 – 6.1 m (15 – 20 ft)
Liquid storage tanks 9.1 m (30 ft)
Reinforced concrete buildings 15.2 m (50 ft)
Dwellings 30.5 m (100 ft)
Computers (not isolated) 91.4 m (300 ft)
8-7.3.3 Vibroflotation. A cylindrical penetrator about 381 mm (15 in) in diameter
and 1.8 m (6 ft) long, called a vibroflot, is attached to an adapter section containing lead
wires and hoses. A crane handles the whole assembly. A rotating eccentric weight
inside the vibroflot develops a horizontal centrifugal force of about 89 kN (10 tons) at
1800 revolutions per minute. Total weight is about 18 kN (2 tons).
To sink the vibroflot to the desired treatment depth, a water jet at the tip is
opened and sets in conjunction with the vibrations so that a hole can be advanced at a
rate of about 1.2 m (3.6 ft) per minute; then the bottom jet is closed, and the vibroflot is
withdrawn at a rate of about 30 mm (0.1 ft) per minute. Newer, heavier vibroflots
operating at 100 horsepower can be withdrawn at twice this rate and have a greater
effective penetration depth. Concurrently, a cohesionless sand or gravel backfill is
dumped in from the ground surface and densified. Backfill consumption is at a rate of
about .62 to 1.77 m3
per m2
(0.7 to 2 cubic yards per square yard) of surface. In partly
saturated sands, water jets at the top of the vibroflot can be opened to facilitate
liquefaction and densification of the surrounding ground. Liquefaction occurs to a radial
distance of 305 mm to 610 mm (1 to 2 ft) from the surface of the vibroflot. Most
vibroflotation applications have been to depths less than 18 m (60 ft), although depths
of 27 m (90 ft) have been attained successfully.
A relationship between probable relative density and vibroflot hold
spacings is given in Figure 8-7.4. Newer vibroflots result in greater relative densities.
Figure 8-7.5 shows relationships between allowable bearing pressure to limit
8-82

Table 8-7.1 Stabilization of Soils for the Foundations of Structures
Method Principle Most
Suitable
Soil
Condition/
Type
Maximum
Effective
Treatment
Depth
(feet)
Economical
Size of
Treated
Area
Special
Materials
Required
Special
Equipment
Required
Properties
of Treated
Material
Special
Advantages
and
Limitations
Relative
Costs
(1976)
Mix in Place
Piles and
Walls
Lime,
cement or
asphalt
introduced
through
rotating
auger or
special in-
place mixer
All soft or
loose
inorganic
soils
>20m Small Cement, lime,
or chemical
stabilization.
Drill rig,
rotating
cutting and
mixing head,
additive
proportioning
equipment
Modified soil
piles or walls
of relatively
high strength.
Does native
soil, reduced
lateral
support
requirements
during
excavation;
difficult to
exert quality
control.
Moderate
to high
Strips and
Membranes
Horizontal
toenails or
membranes
buried in
soil under
footings
All A few
meters
Small Metal or
plastic strips,
polyethylene,
polypropylene,
or polyester
fabrics
Excavation,
earth
handling and
compaction
equipment.
Increased
bearing
capacity ,
reduced
deformations.
Increased
allowable
bearing
pressures,
requires
over-
excavation
for footings.
Low to
moderate
Reinforcement
Vibro-
replacement
stone
columns
Hole jetted
into soft
fine grain
soils /
backfilled
w/ dense,
compacted
gravel
Soft clays
and
alluvial
deposits
20 m >1500 m
2
Gravel or
crushed rock
backfill
Vibroflot.
crane or
vibro-cat,
water
Increased
bearing
capacity;
reduced
settlements
Faster than
pre-
compression.
No
dewatering;
limited
bearing
capacity
Moderate
to high,
relative to
depth
penetration.

Suitable
Soil
Condition/
Type
Maximum
Effective
Treatment
Depth
(feet)
Economical
Size of
Treated
Area
Special
Materials
Required
Special
Equipment
Required
Properties
of Treated
Material
Special
Advantages
and
Limitations
Relative
Costs
(1976)
Heating Drying at low
temperatures;
alteration of
clays of
intermediate
temps (400 –
600 o
C):
Fusion @
high temps
(> 1000O
C)
Fine
grained
soils;
especially
partiall y
saturated
silts and
clays:
loess
15 m Small Selected
fuels
Fuel tanks,
burners,
blowers
Reduced
water
control,
plasticity,
water
sensitivity;
increased
strength
Can obtain
irreversible
improvements
in properties;
introduces
stabilization
w/ hot gases.
Experimental
@ this writing
( 1976)
High
Thermal
Freezing Freezes soft,
wet ground to
increase
strength,
reduce
pliability
All soils Several m Small Refrigerant Refrigeration
system
Increased
strength,
reduced
pliability
Cannot be
used with
flowing
ground water;
temporary.
High

UFC 3-220-01N
15 AUGUST 2005
consolidation strength and strength gain should be checked during fill placement by
means of piezometers, borings, laboratory tests, and in-situ strength tests.
8-7.5.2 Vertical Drains. The required preloading time for most soft clay deposits
more than about 1.5 to 3 m (5 to 10 ft) thick will be large. Providing a shorter drainage
path by installing vertical sand drains may reduce the consolidation time. Sand drains
are typically 254 to 370 mm (10 to 15 in) in diameter and are installed at spacings of 1.5
to 4.5 m (5 to 15 ft). A sand blanket or a collector drain system is placed over the
surface to facilitate drainage. Other types of drains available are special cardboard or
combination plastic-cardboard drains. Provisions should be made to monitor pore
pressures and settlements with time to determine when the desired degree of pre-
compression has been obtained.
Both displacement and non-displacement methods have been used for installing sand
drains. Although driven, displacement drains are less expensive than augured or
"bored" non-displacement drains; they should not be used in sensitive deposits or in
stratified soils that have higher hydraulic conductivity in the horizontal than in the
vertical direction. Vertical drains are not needed in fibrous organic deposits because
the hydraulic conductivity of these materials is high, but they may be required in
underlying soft clays.
8-7.5.3 Dynamic Consolidation (Heavy Tamping). Densification by heavy
tamping has also been reported as an effective means for improving silts and clays, with
preconstruction settlements obtained about 2 to 3 times the predicted construction
settlement. The time required for treatment is less than for surcharge loading with sand
drains. The method is essentially the same as that used for cohesionless soils, except
that more time is required. Several blows are applied at each location followed by a 1-
to 4-week rest period, then the process is repeated. Several cycles may be required. In
each cycle the settlement is immediate, followed by drainage of pore water. Drainage is
facilitated by the radial fissures that form around impact points and by the use of
horizontal and peripheral drains. Because of the necessity for a time lapse between
successive cycles of heavy tamping when treating silts and clays, a minimum treatment
area of 15,000 to 30,000 m2
(18,000 to 35,000 sq yd) is necessary for economical use
of the method. This method is presently considered experimental in saturated clays.
8-7.5.4 Electro osmosis. Soil stabilization by electro osmosis may be effective
and economical under the following conditions: (1) a saturated silt or silty clay soil, (2) a
normally consolidated soil, and (3) a low pore water electrolyte concentration. Gas
generation and drying and fissuring at the electrodes can impair the efficiency of the
method and limit the magnitude of consolidation pressures that develop. Treatment
results in non-uniform changes in properties between electrodes because the induced
consolidation depends on the voltage, and the voltage varies between anode and
cathode. Thus, reversal of electrode polarity may be desirable to achieve a more
uniform stress condition. Electro osmosis may also be used to accelerate the
consolidation under a preload or surcharge fill. The method is relatively expensive.
8-99

UFC 3-220-01N
15 AUGUST 2005
8-19
• Plastic soils with high natural moisture are difficult to process for proper
moisture for compaction
• Stratified soils may require extensive mixing of borrow.
8-1.6.2 Embankments on Stable Foundation. The side slopes of fills not
subjected to seepage forces ordinarily vary between 1 on 1-1/2 and 1 on 3. The
geometry of the slope and berms are governed by requirements for erosion control and
maintenance. See Engineering Manual for Slope Stability Studies for procedures to
calculate stability of embankments.
8-1.6.3 Embankments on Weak Foundations. Weak foundation soils may
require partial or complete removal, flattening of embankment slopes, or densification.
Analyze cross-section stability by methods of UFC 3-220-10N.
8-1.6.4 Embankment Settlement. Settlement of an embankment is caused by
foundation consolidation, consolidation of the embankment material itself, and
secondary compression in the embankment after its completion.
• See UFC 3-220-10N for procedures to decrease foundation settlement or
to accelerate consolidation.
• Significant excess pore pressures can develop during construction of fills
exceeding about 80 ft in height or for lower fills of plastic materials placed
wet of optimum moisture. Dissipation of these excess pore pressures
after construction results in settlement. For earth dams and other high fills
where settlement is critical, construction pore pressures should be
monitored by the methods of UFC 3-220-10N.
• Even for well-compacted embankments, secondary compression and
shear strain can cause slight settlements after completion. Normally this
is only of significance in high embankments, and can amount to between
0.1 and 0.2 percent of fill height in three to four years or between 0.3 and
0.6 percent in 15 to 20 years. The larger values are for fine-grained
plastic soils.

UFC 3-220-01N
15 AUGUST 2005
occurrence be recorded. Materials encountered should be identified in accordance with
the Unified Soil Classification System (ASTM D 2487), including the frozen soil
classification system, as presented in UFC 3-130-01.
11-3.3.4 Seasonal Frost Areas. In seasonal frost areas, the most essential site
date beyond those needed for nonfrost foundation design is the design freezing index
and the soil frost-susceptibility characteristics. In permafrost areas, as described in
UFC 3-130-01, the date requirements are considerably more complex; determination of
the susceptibility of the foundation materials to settlement on thaw and of the
subsurface temperatures and thermal regime will usually be the most critical special
requirements. Ground temperatures are measured most commonly with
copper-constantan thermocouples or with thermistors.
11-3.3.5 Special Site Investigations. Special site investigations, such as
installation and testing of test piles, or thaw-settlement tests may be required.
Assessment of the excavation characteristics of frozen materials may also be a key
factor in planning and design.
11-4 FOUNDATION DESIGN
11-4.1 Selection of Foundation Type. Only sufficient discussion of the
relationships between foundation conditions and design decisions is given below to
indicate the general nature of the problems and solutions. Greater detail is given in
UFC 3-220-10N.
11-4.1.1 Foundations in Seasonal Frost Areas. When foundation materials
within the maximum depth of seasonal frost penetration consist of clean sands and
gravels or other non-frost-susceptible materials that do not develop frost heave, thrust,
or thaw weakening, design in seasonal frost areas may be the same as for non-frost
regions, using conventional foundations, as indicated in Figure 11-4. Effect of the frost
penetration on related engineering aspects, such as surface and subsurface drainage
systems or underground utilities, may need special consideration. Thorough
investigations should be made to confirm the non-frost susceptibility of subgrade soils
prior to design for this condition.
When foundation materials within the annual frost zone are
frost-susceptible, seasonal frost heave and settlement of these materials may occur. In
order for ice segregation and frost heave to develop, freezing temperatures must
penetrate into the ground, soil must be frost-susceptible, and adequate moisture must
be available. The magnitude of seasonal heaving is dependent on such factors as rate
and duration of frost penetration, soil type and effective pore size, surcharge, and
degree of moisture availability. Frost heave in a freezing season may reach a foot or
more in silts and some clays if there is an unlimited supply of moisture available. The
frost heave may lift or tilt foundations and structures, commonly differentially, with a
variety of possible consequences. When thaw occurs, the ice within the frost-heaved
soil is changed to water and escapes to the ground surface or into surrounding soil,
allowing overlying materials and structures to settle. If the water is released by thaw
more rapidly than it can be drained away or redistributed, substantial loss in soil
11-9

UFC 3-220-01N
15 AUGUST 2005
CHAPTER 12
DESIGN FOR EQUIPMENT VIBRATIONS AND SEISMIC LOADINGS
12-1 INTRODUCTION
12-1.1 Introduction. Vibrations caused by steady state or transient loads may
cause settlement of soils, excessive motions of foundations or structures, or discomfort
or distress to personnel. Some basic design factors for dynamic loading retreated in
this action. Design of a foundation system incorporates the equipment lading,
subsurface material properties, and geometrical proportions in some analytical
procedure.
12-1.1.1 Vibration Criteria. Figure 12-1 shows some limiting values of vibration
criteria for machines, structures, and personnel. On this diagram, vibration
characteristic: are described in terms of frequency and peak amplitudes of acceleration,
velocity, or displacement. Values of frequency constitute the abscissa of the diagram
and peak velocity is the ordinate. Values of peak displacement are read along one set
of diagonal lines and labeled in displacement (inches), and peak acceleration values are
read along the other set of diagonal lines and labeled in various amounts of g, the
acceleration of gravity. The shaded zones in the upper right-hand corner indicate
possible structural damage to walls by steady-state vibrations. For structural safety
during blasting, limit peak velocity to 50 mm (2 in) per second and peak acceleration to
0.10g for frequencies exceeding 3 cycles per second. These limits may occasionally
have to be lowered to avoid being excessively annoying to people.
12-1.1.2 Equipment Vibration Criteria. For equipment vibration, limiting criteria
consist of a maximum velocity of 1.0 inch per second up to a frequency of about 30
cycles per second and a peak acceleration of 0.15 g alive this frequency, however, this
upper limit is for safety only, and specific criteria must be established for each
installation. Usually, operating limits of equipment are based on velocity criteria; greater
than 0.5 inch per second indicates extremely rough operation and machinery should be
shut down; up to 0.25 mm (0.1 in) per second occurs for smooth, well-balanced
equipment; and less than 0.025 mm (0.01 in) per second represents very smooth
operation.
12-1.1.3 Vibration Affect on Personnel. Figure 12-1 also includes peak velocity
criteria for reaction of personnel to steady-state abrasions. Peak velocities greater than
0.25 mm (0.1 in) per second are “troublesome to persons,” and peak velocities of 0.025
mm (0.01 in) per second are just “barely noticeable to persons.” It is significant that
persons and machines respond to equivalent levels of vibration. Furthermore, persons
may notice vibrations that are about 1/100 of the value related to safety of structure.
12-1.2 Single Degree of Freedom, Damped Forced Systems. Vibrations of
foundation-soil systems can adequately be represented by simple mass-spring-dashpot
systems. The model for this simple system consists of a concentrated mass, m,
supported by a linear elastic spring with a spring constant, k, and a viscous damping
unit (dashpot) having a damping constant, c. The system is excited by an external
12-1

Table 8-1.4
Typical Properties of Compacted Soils
Typical
Value of
Compression
Typical Strength CharacteristicsGroup
Symbol
Soil
Type
Range of
Maximum
Dry Unit
Weight,
gm/cm3
(lbs/ft3)
Range of
Optimum
Moisture,
Percent At
134
kPa
(1.4
tsf)
At
345
kPa
(3.6
tsf)
Cohesion
(as
Compacted)
kPa
(lb/ft
2
)
Cohesion
(Saturated)
kPa
(lb/ft2
)
Effective
Stress
Envelope
Deg
Tan
Typical
Coefficient
of
Permeability
cm/min
(ft/min)
Range
of
CBR
Values
Range of
Subgrade
Modulus
k
gm/cm3
(lbs/ft3)
SW Well
graded
clean
sands,
gravelly
sands
1.762 –
2.082
(110 –
130)
16 – 9 0.6 1.2 0 0 38 0.79 3 x 10-2
(>10-3
)
20 –
40
5,500 –
8,300
(200 –
300)
SP Poorly
graded
clean
sands,
sand
gravel
mix
1.602 –
1.922
(100 –
120)
21 – 12 0.8 1.4 0 0 37 0.74 3 x 10-2
(>10-3
)
10 –
40
5,500 –
8,300
(200 –
300)
SM Silty
soils,
poorly
graded
sand-silt
mix
1.762 –
2.002
(110 –
125)
16 – 11 0.8 1.6 50 (1050) 20 (420) 34 0.67 1.5 x 10-3
(>5 x > 10-5
)
10 –
40
5,500 –
8,300
(200 –
300)
SM –
SC
Sand-
silt clay
mix with
slightly
plastic
fines
1.762 –
2.082
(110-
130)
15 – 11 0.8 1.4 50 (1050) 14 (300) 33 0.68 >6 x 10-5
(>2 x 10-6
)
5-30 2,800 –
8,300
(100-300)

UFC 3-220-01N
15 AUGUST 2005
Figure 12-2 Response Curves for the Single-Degree-of-Freedom System with
Viscous Damping
Figure 12-3 Six Modes of Vibration for a Foundation
12-5

Table 8-1.4
Typical Properties of Compacted Soils
Typical
Value of
Compression
Typical Strength CharacteristicsGroup
Symbol
Soil
Type
Range of
Maximum
Dry Unit
Weight,
gm/cm3
(lbs/ft3)
Range of
Optimum
Moisture,
Percent At
134
kPa
(1.4
tsf)
At
345
kPa
(3.6
tsf)
Cohesion
(as
Compacted)
kPa
(lb/ft
2
)
Cohesion
(Saturated)
kPa
(lb/ft2
)
Effective
Stress
Envelope
Deg
Tan
Typical
Coefficient
of
Permeability
cm/min
(ft/min)
Range
of
CBR
Values
Range of
Subgrade
Modulus
k
gm/cm3
(lbs/ft3)
MH Inorga-
nic clay
silts/el-
astic silt
1.121 -
1.522
(70-95)
40-24 2.0 3.8 73 (1500) 20 (420) 25 0.47 >1.5 x 10-5
(>5 x 10-7
)
10 or
less
1,400 –
2,800
(50-100)
CH Inorga-
nic
clays of
high
plasti-
city
1.201 –
1.682
(75-105)
36-19 2.6 3.9 342 (7150) 11 (230) 19 0.35 >3 x 10
-6
(>10-7
)
15 or
less
700 –
3,500
(50-150)
OH Organic
& silty
clays
1.041 –
1.602
(65-100)
45-21 *** *** ***** ***** **** **** **** 5 or
less
350 –
2800 (25-
100)
Notes:
1. All properties are for conditions of “Standard Proctor” maximum density, except volume of “ k “ and CBR which are for “Modified Proctor”
maximum density.
2. Typical strength characteristics are for effective envelopes and are obtained USBR data.
3. Compression values are for vertical loading with complete lateral containment.
4. (>) indicates that typical property I greater than the value shown. Asterisks (*) indicate insufficient data available for an estimate.

Table 8-1.5
Relative Desirability of Soils as Compacted Fill
Relative Desirability for Various Uses
Rolled Earth Fill
Dams
Canal
Sections
Foundations Roadways
Fills
Group
Symbol
Soil Type
Homogeneous
Embankment
Core
Shell
ErosionResistance
CompactedEarth
Lining
mportant
H
Seepage
Important
SeepageNot
I
FrostHeave
NotPossible
Frosteave
Possible
Surfacing
ML Inorganic silts and very
fine sands. Rock flower,
silty or clayey fine sands
with slight plasticity.
6 6 - - 6
Erosion
critical
6 9 10 11 _
CL Inorganic clays of low to
medium plasticity,
gravelly clays, sandy
clays, silty clays, lean
clays.
5 3 - 9 3 5 10 9 7 7
OL Organic silts and organic
silts-clays of low plasticity
8 8 - - 7
Erosion
critical
7 11 11 12 -
MH Inorganic silts, micaceous
or diatomaceous fine
sandy or silty soils, elastic
silts.
9 9 - - - 8 12 12 13 -
CH Inorganic clays of high
plasticity, fat clays
7 7 - 10 8
volume
change
critical
9 13 13 8 -
OH Organic clays of medium
high plasticity
10 10 - - - 10 14 14 14 -
(-) indicates not appropriate for this type of use.

UFC 3-220-01N
15 AUGUST 2005
8-1.6.5 Earth Dam Embankments. Evaluate stability at three critical stages: the
end of construction stage, steady state seepage stage, and rapid drawdown stage. See
UFC 3-220-10N for pore pressure distribution at these stages. Seismic forces must be
included in the evaluation. Requirements for seepage cutoff and stability dictate design
of cross section and utilization of borrow materials.
8-1.6.5.1 Seepage Control. Normally the earthwork of an earth dam is zoned with
the least pervious, fine-grained soils in the central zone and coarsest, most stable
material in the shell. Analyze seepage by the methods of UFC 3-220-10N.
• Consider the practicability of a positive cutoff trench extending to
impervious strata beneath the embankment and into the abutments.
• For a properly designed and constructed zoned earth dam, there is little
danger from seepage through the embankment. Drainage design
generally is dictated by necessity for intercepting seepage through the
foundation or abutments. Downstream seepage conditions are more
critical for homogeneous fills. See UFC 3-220-10N for drainage and filter
requirements.
8-1.6.5.2 Piping and Cracking. A great danger to earth dams, particularly those of
zoned construction, is the threat of cracking and piping. Serious cracking may result
from tension zones caused by differences in stress-strain properties of zoned material.
See Figure 1 (Influence of Soil Properties and Construction Methods on the
Performance of Homoaeneous Earth Dams) for classification of materials according to
resistance to piping or cracking. Analyze the embankment section for potential tension
zone development. Place an internal drainage layer immediately downstream of the
core to control seepage from possible cracking if foundation settlements are expected to
be high.
8-1.6.5.3 Dispersive soil. Dispersive clays should not be used in dam
embankments. Determine the dispersion potential using Table 8-1.6. A hole through a
dispersive clay will increase in size as water flows through (due to the breakdown of the
soil structure), whereas the size of a hole in a non-dispersive clay would remain
essentially constant. Therefore, dams constructed with dispersive clays are extremely
susceptible to piping.
8-26

UFC 3-220-01N
15 AUGUST 2005
FIGURE 8-1.12
Resistance of Earth Dam. Embankment Materials To Piping and Cracking
8-27

UFC 3-220-01N
15 AUGUST 2005
FIGURE 8-1.12 (continued)
Resistance of Earth Dam Embankment Materials To Piping and Cracking
8-28

UFC 3-220-01N
15 AUGUST 2005
8-1.7 Borrow Excavation
8-1.7.1 Borrow Pit Exploration. Make exploratory investigations to determine
the suitable sources of borrow material. Laboratory tests to determine the suitability of
available materials include natural water contents, compaction characteristics,
grain-size distribution, Atterberg limits, shear strength, and consolidation. Typical
properties of compacted materials for use in preliminary analyses are given in Table 8-
1.4. The susceptibility to frost action also should he considered in analyzing the
potential behavior of fill material. The scope of laboratory testing on compacted
samples depends on the size and cost of the structure, thickness and extent of the fill,
and also strength and compressibility of underlying soils. Coarse-grained soils are
preferred for fill; however, most fine-grained soils can be used advantageously if
attention is given to drainage, compaction requirements, compaction moisture, and
density control.
The number and spacing of borings or test pits for borrow exploration must be sufficient
to determine the approximate quantity and quality of construction materials within an
economical haul distance from the project. For mass earthwork, initial exploration
should be on a 61 meters (200 foot) grid. If variable conditions are found during the
initial explorations, perform intermediate borings or test pits. Explorations should
develop the following information:
• A reasonably accurate subsurface profile to the anticipated depth of
excavation
• Engineering properties of each material considered for use
• Approximate volume of each material considered for use
• Water level
• Presence of salts, gypsums, or undesirable minerals
• Extent of organic or contaminated soils, if encountered
8-1.7.2 Excavation Methods. Consider the following when determining
excavation methods:
• Design and efficiency of excavation equipment improves each year.
Check various construction industry publications for specifications.
• Determine rippability of soil or rock by borings (RQD and core recovery,
see UFC 3-220-10N), geophysical exploration, and/or trial excavation.
8-1.7.3 Utilization of Excavated Materials. In the process of earthmoving there
may be a reduction of the volume ("shrinkage") because of waste and densification, or
an increase of volume ("swell") in the case of rock or dense soils, because the final
density is less than its original density.
8-30
Determine total borrow volume, VB, required for compacted fill as follows:

UFC 3-220-01N
15 AUGUST 2005
The volume of borrow soil required should be increased according to the volume
change indicated above. A "shrinkage" factor of 10 to 15 percent may be used for
estimating purposes. Note that a large percentage of cobble size material will increase
the waste, because sizes larger than 3 inches are generally excluded from compacted
fill.
Note the following for Rock Fill:
• Maximum expansion ("swell") from in-situ conditions occurs in dense, hard
rock with fine fracture systems that breaks into uniform sizes. Unit volume
in a quarry will produce approximately 1.5 volumes in fill.
• Minimum expansion occurs in porous, friable rock that breaks into broadly
graded sizes with numerous spalls and fines. Unit volume in quarry will
produce approximately 1.1 volumes in fill.
8-2 FILL
8-2.1 Types of Fill. Fills include conventional compacted fills; hydraulic fills;
and uncontrolled fills of soils or industrial and domestic wastes, such as ashes, slag,
chemical wastes, building rubble, and refuse. Properly placed compacted fill will be
more rigid and uniform and have greater strength than most natural soils. Hydraulic fills
may be compacted or uncompacted and are an economical means of providing fill over
large areas. Except when cohesionless materials, i.e., clean sands and gravels, are
placed under controlled conditions so silty pockets are avoided and are compacted as
they are placed, hydraulic fills will generally require some type of stabilization to ensure
adequate foundations.
Uncontrolled fills are likely to provide a variable bearing capacity and result in a non-
uniform settlement. They may contain injurious chemicals and, in some instances, may
be chemically active and generate gases that must be conducted away from the
structure. Subject foundations on fills of the second and third groups (and the first
group if not adequately compacted) to detailed investigations to determine their
8-31

UFC 3-220-01N
15 AUGUST 2005
suitability for supporting a structure, or else they should be avoided. Unsuitable fills
often can be adequately stabilized.
8-2.2 Foundations on Compacted Fills
8-2.2.1 Compacted Fill Beneath Foundations. Compacted fills are used
beneath foundations where it is necessary to raise the grade of the structure above
existing ground or to replace unsatisfactory surface soils. Fills constructed above the
natural ground surface increase the load on underlying soils, causing larger settlements
unless construction of the structure is postponed until fill induced settlements have
taken place. Settlements beneath a proposed fill can be computed using methods
outlined in Chapter 4. If computed settlements are excessive, consider surcharging and
postponing construction until the expected settlement under the permanent fill loading
has occurred. Extend the fill well beyond the loading area, except where the fill is
placed against a cut slope. Where the fill is relatively thick and is underlain by soft
materials, check its stability with respect to deep sliding. If the fill is underlain by
weaker materials, found the footings on the fill unless settlement is excessive. If the fill
is underlain by a stronger material, the footings may be founded on the fill or on the
stronger material.
8-2.2.2 Foundations Partially on Fill. Where a sloping ground surface or
variable foundation depths would result in supporting a foundation partially an natural
soil, or rock, and partially on compacted fill, settlement analyses are required to
estimate differential settlements. In general, a vertical joint in the structure should be
provided, with suitable architectural treatment, at the juncture between the different
segments of foundations. The subgrade beneath the portions of foundations to be
supported on natural soils or rock should be undercut about 1 meters (3 feet) and
replaced by compacted fill that is placed at the same time as the fill for the portions to
be supported on thicker compacted fill.
8-2.2.3 Design of Foundations on Fill. Foundations can be designed on the
basis of bearing capacity and settlement calculations described in Chapter 10. The
settlement and bearing capacity of underlying foundation soils also should be evaluated.
Practically all types of construction can be founded on compacted fills, provided the
structure is designed to tolerate anticipated settlements and the fill is properly placed
and compacted. Good and continuous field inspection is essential.
8-2.2.4 Site Preparation. The site should be prepared by clearing and grubbing
all grass, trees, shrubs, etc. Save as many trees as possible for environmental
considerations. Strip and stockpile the topsoil for later landscaping of fill and borrow
areas. Placing and compacting fills should preferably be done when the area is still
unobstructed by footings or other construction. The adequacy of compacted fills for
supporting structures is dependent chiefly on the uniformity of the compaction effort.
Compaction equipment generally can be used economically and efficiently only on large
areas. Adverse weather conditions may have a pronounced effect on the cost of
compacted fills that are sensitive to placement moisture content, e.g., on materials
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UFC 3-220-01N
15 AUGUST 2005
having more than 10 to 20 percent finer than the No. 200 sieve, depending on
gradation.
8-2.2.5 Site Problems. Small building areas or congested areas where many
small buildings or utility lines surround the site present difficulties in regard to
maneuvering large compaction equipment. Backfilling adjacent to structures also
presents difficulties, and power handtamping equipment must be employed, with
considerable care necessary to secure uniform compaction. Procedures for backfilling
around structures are discussed in this Chapter.
8-2.3 Compaction Requirements
8-2.3.1 General. Guidelines for selecting compaction equipment and for
establishing compaction requirements for various soil types are given in table 8-2.1.
When fill materials have been thoroughly investigated and there is ample local
experience in compacting them, it is preferable to specify details of compaction
procedures, such as placement water content, lift thickness, type of equipment, and
number of passes. When the source of the fill or the type of compaction equipment is
not known beforehand, specifications should be based on the desired compaction
result, with a specified minimum number of coverage of suitable equipment to assure
uniformity of compacted densities.
8-2.3.2 Compaction Specifications. For most projects, the placement water
content of soils sensitive to compaction moisture should be within the range of - 1 to + 2
percent of optimum water content for the field compaction effort applied. Each layer is
compacted to not less than the percentage of maximum density specified in Table 8-2.2.
It is generally important to specify a high degree of compaction in fills under structures
to minimize settlement and to ensure stability of a structure. In addition to criteria set
forth in Chapter 8, consider the following factors in establishing specific requirements:
• The sensitivity of the structure to total and differential settlement as related
to structural design is particularly characteristic of structures to be founded
partly on fill and partly on natural ground.
• If the ability of normal compaction equipment to produce desired densities
in existing or locally available materials within a reasonable range of
placement water content is considered essential, special equipment
should be specified.
• The compaction requirements for clean, cohesionless, granular materials
will be generally higher than those for cohesive materials, because
cohesionless materials readily consolidate, or liquefy, when subjected to
vibration. For structures with unusual stability requirements and
settlement limitations, the minimum density requirements indicated in table
15-2 should be increased. For coarse-grained, well-graded, cohesionless
soils with less than 4 percent passing the 0.075 Micron (No. 200) sieve, or
for poorly graded cohesionless soils with less than 10 percent, the
material should be compacted at the highest practical water content,
preferably saturated. Compaction by vibratory rollers generally is the most
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UFC 3-220-01N
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effective procedure. Experience indicates that pervious materials can be
compacted to an average relative density of 85 ± 5 percent with no
practical difficulty. For cohesionless materials, stipulate that the fill be
compacted to either a minimum density of 85 percent relative density or
95 percent of compaction effort, whichever giver, the greater density.
• If it is necessary to use fill material having a tendency to swell, the
material should be compacted at water contents somewhat higher than
optimum and to no greater density than required for stability under
proposed loadings (Table 8-2.1). The bearing capacity and settlement
characteristics of the fill under these conditions should be checked by
laboratory tests and analysis. Swelling clays can, in some instances, be
permanently transformed into soils of lower plasticity and swelling
potential by adding a small percentage of hydrated lime (Chapter 16).
8-2.3.3 Compacted Rock. Compacted crushed rock provides an excellent
foundation fill. Vibratory rollers are preferable for compacting rock. Settlement of fill
under the action of the roller provides the most useful information for determining the
proper loose lift thickness, number of passes, roller type, and material gradation.
Compaction with an 89 kN (10-ton) vibratory roller is generally preferable. The rock
should be kept watered at all times during compaction to obviate collapse settlement on
loading and first wetting. As general criteria for construction and control testing of rock
fill are not available, test fills should be employed where previous experience is
inadequate and for large important rock fills.
8-2.4 Placing And Control Of Backfill. Backfill should be placed in lifts no
greater than shown in Table 8-2.1, preferably 200 mm (8 inches) or less and depending
on the soil and type of equipment available. No backfill should be placed that contains
frozen lumps of soil, as later thawing will produce local soft spots. Do not place backfill
on muddy, frozen, or frost-covered ground. Methods of compaction control during
construction are described in paragraph 8-3.
8-2.5 Fill Settlements. A fill thickness of even 1 m (3 ft) is a considerable soil
load, which will increase stresses to a substantial depth (approximately 2B, where B =
smallest lateral dimension of the fill). Stress increases from the fill may be larger than
those from structure footings placed on the fill. Use procedures outlined in chapter 10
to obtain expected settlements caused by fill loading. Many fills are of variable
thickness, especially where an area is landscaped via both cutting and filling to obtain a
construction site. In similar cases, attention should be given to building locations with
respect to crossing cut and fill lines so that the proper type of building settlement can be
designed (building may act as a cantilever, or one end tends to break off, or as a beam
where the interior sags). Proper placing of reinforcing steel in the wall footings (top for
cantilever action or bottom for simple beam action) may help control building cracks
where settlement is inevitable; building joints can be provided at critical locations if
necessary. The combined effect of structure (one- and two-story residences) and fill
loading for fills up to 3 m (10 ft) in thickness on sound soil and using compaction control
8-34

UFC 3-220-01N
15 AUGUST 2005
email pilebuck@pilebuck.com
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7. ASTM International
100 Barr Harbor Drive
P.O. Box C700
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Pennsylvania, USA 19428-2959
Tel: 610-832-9585
FAX 610-832-9555
http://www.astm.org/
8. International Code Council
5203 Leesburg Pike
Suite 600
Falls Church, VA 22041
Tel: 703-9311-44533
FAX703-379-1546
Email: webmaster @iccsafe.org
http://www.iccsafe.org
9. Braja Das
10. The Geotechnical and
Geoenvironmental Software Directory
http://www.ggsd.com/
11. The Geotechnical Directory
Breakwaters, Jetties, Bulkheads and
Seawalls
Coastal Protection
Cellular Cofferdams
Steel Sheet Piling Design Manual
Pile Hammer Specifications
ASTM D2487, Standard Classification of
soils for Engineering Purposes (Unified
Soil Classification System
D 2488, Standard Practice for Description
and Identification of Soils (Visual-Manual
Procedure)
D 5578, Standard Guide for Using Rock
Mass Classification Systems for
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2000 International Building Code (IBC
2000) Chapter 18
FEMA 273.4, 274.4, 302, 303
Accompany IBC 2000,
Fundamentals of Geotechnical
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Catalogues 1306 programs in the fields of
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A good resource for making University
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A-6

UFC 3-220-01N
15 AUGUST 2005
8-36
8-2.6.3 Settlements of Hydraulic Fills. If the coefficient of permeability of a
hydraulic fill is less than 0.0616 mm/minute (0.0002 ft/minute), the consolidation time for
the fill will be long and prediction of the behavior of the completed fill will be difficult. For
coarse-grained materials with a larger coefficient of permeability, fill consolidation and
strength buildup will be relatively rapid and reasonable strength estimates can be made.
Where fill and foundation soils are fine-grained with a low coefficient of permeability,
piezometers should be placed both in the fill and in the underlying soil to monitor pore
pressure dissipation. It may also be necessary to place settlement plates to monitor the
settlement. Depending on the thickness of the fill, settlement plates may be place both
on the underlying soil and within the fill to observe settlement rates and amounts.
8-2.6.4 Compaction of Hydraulic Fills. Dike-land hydraulic fills can be
compacted as they are placed by use of the following:
• Driving track-type tractors back and forth across the saturated fill.
(Relative densities of 70 to 80 percent can be obtained in this manner for
cohesionless materials.)
• Other methods such as vibratory rollers, vibro-flotation, terraprobing, and
compaction piles. Below water, hydraulic fills can be compacted by use of
terraprobing, compaction piles, and blasting.
8-2.6.5 Underwater Hydraulic Fills. For structural fill placed on a dredged
bottom, remove the fines dispersed in dredging by a final sweeping operation,
preferably with suction dredges, before placing the fill. To prevent extremely flat slopes
at the edge of a fill, avoid excessive turbulence during dumping of the fill material by
placing with clamshell or by shoving off the sides of deck barges. To obtain relatively
steep slopes in underwater fill, use mixed sand and gravel. With borrow containing
about equal amounts of sand and gravel, underwater slopes as steep as 1V on 2H may
be achieved by careful placement. Uncontrolled bottom dumping from barges through
great depths of water will spread the fill over a wide area. To confine such fill, provide
berms or dikes of the coarsest available material or stone on the fill perimeter.

Table 8-2.1
A Summary of Densification Methods for Building Foundations
Fill and Backfill Deep Foundation Deposits
Typical Equipment and Procedures for Compaction
Soil
Group
Soil
Types
Degree of
Compaction
Equipment No. of
Phases or
Coverages
Comp.
Lift
Thick.,
mm (in)
Placement
Water
Content
Field
Control
Compaction Methods Field Control
Vibratory
rollers and
compactors
Indefinite Indefinite
Rubber tired
rollersa
2-5
coverages
300 (12)
Crawler type
tractorc
2-5
coverages
130 (5)
Compacted
90 to 95%
ASTM D
1557
maximum
density
75 to 85%
of relative
density
Power hand
tamperc
Indefinite 150 (6)
Saturate by
flooding
Control
samples at
intervals to
determine
degree of
compaction
or relative
density
None available
except for near
surface (down to
approximate depth of
five feet)
Compaction by
equipment and
procedure shown at
left
Rubber tired
rollera
2-5
coverages
360 (14)
Crawler type
tractor
1-2
coverages
250 (10)
Power hand
tamper
Indefinite 200 (8)
Pervious(FreeDraining)
GW
GP
SW
SP
Semicompacted
85 to 90%
ASTM D
1557
maximum
density
65 to
75% of
relative
density Controlled
routing of
construction
equipment
Indefinite 200 –
250
(8-10)
Saturate by
flooding
Control
samples
per above,
if needed
Vibroflotation,
compaction piles,
sand piles,
explosives
Surface compaction
as per above
Undisturbed
samples from
borings or test pits
to determine
degree of
compaction or
relative density

Table 8-2.1
A Summary of Densification Methods for Building Foundations
Fill and Backfill Deep Foundation Deposits
Soil
Group
Soil
Types
Degree of
Compaction
Equipment No. of
Phases or
Coverages
Lift
Thick.,
mm (in)
Placement
Water
Content
Field
Control
Compaction Methods Field Control
Rubber tired
roller (a)
2-5
coverages
200 (8)
Sharpefoot
roller (d)
4-8 passes 150 (6)
Compacted
90 – 95%
ASTM D 1557
maximum
density
Power hand
tamper ( c )
Indefinite 100 (4)
Optimum
water
content
based on
ASTM D
1557
Control
samples at
intervals to
determine
degree of
compaction
Rubber tired
roller (a)
2-4
coverages
250 (10)
Sharpefoot
roller (d)
4-8 passes 200 (8)
Crawler
type tractor
(b)
3
coverages
150 (6)
Power hand
tamper (d)
Indefinite 150 (6)
Semi-ImperviousandImpervious
GM
GC
SM
SC
ML
CL
OL
OH
MH
CH
Semicompacted
85-90%
ASTM D 1557
maximum
density
Control of
construction
equipment
Indefinite 150 –
200 (6-
8)
(A) Optimum
water content
based on
ASTM D 1557.
(B) Wet side
maximum
water content
at which one
material can
satisfactorily
operate,
minimum water
content
required to
bond particles
(and not result
in voids or
honey-combed
materials.)
(A) Control
samples as
noted
above, if
needed.
(B) Field
control
exercised
by visual
inspection
of action of
compaction
equipment.
(A) Surface compaction by equipment
and procedures shown @ left is feasible
only if material is at proper water
content.
(B) Densification of soils is controlled by
consolidation process:
Preload fills*
Lowering of groundwater table
Drying
___________________________
* Consolidation may be accelerated by
means of vertical drains.
Field control exercised by observation of
pore pressures and surface settlements.
Note: The above requirements will be adequate in relation to most construction. In special cases where tolerable settlements are unusually small, it may be necessary to employ additional
compaction equivalent to 95-100% of CE55 compaction effort. A coverage consists of one application of the wheel of a rubber tired roller of the treads of a crawler type tractor over each
point in the area being compacted. For a sharpefoot roller drum over the area being compacted.
a. Rubber tired rollers having a wheel load between 18,000 and 25,000 lbs. and a tire pressure between 80 and 100 psi.
b. Crawler type tractors weighing not less than 20,000 lbs and exerting a foot pressure not less than 6 ½ psi.
c. Power hand tamper weighing more than 100 lbs: pneumatic or operated by gasoline engine.
d. Sharpfoot rollers having a foot pressure between 250 and 500 psi and tamping 7-10 tamp lengths with a face area between 7 and 16 sq. inches.

UFC 3-220-01N
15 AUGUST 2005
Table 8-2.2
Compaction Density as a Percent of ASTM D 1557 Laboratory Test Density
ASTM D 1557 Maximum Density, in Percentage
Cohesive Soils Cohesionless Soils
Fill/Embankment/Backfill
Under proposed structures, building
Slabs, steps, paved areas 90 95a
Under sidewalks and grassed areas 85 90
Sub-grade
Under building slabs, steps and
Paved areas / top 300 mm (12inches) 90 95
Under sidewalks, top 150 mm (6 inches) 85 90
a
Maybe 85% relative density / whichever is higher
8-3 BACKFILL
8-3.1 Introduction. The greatest deficiencies in earthwork operations around deep-
seated or subsurface structures occur because of improper backfilling procedures and
inadequate construction control during this phase of the work. Therefore, primary emphasis in
this section is on backfilling procedures. Design and planning considerations, evaluation and
selection of materials, and other phases of earthwork construction are discussed where
pertinent to successful backfill operations. Although the information in this section is primarily
applicable to backfilling around large and important deep-seated or buried structures, it is also
applicable in varying degrees to backfilling operations around all structures, including conduits.
8-3.2 Planning and Design of Structures and Excavations to Accommodate
Backfill Operations. Many earthwork construction problems can be eliminated or minimized
through proper design, thorough planning, and recognition of problem areas effecting backfill
operations. Recognition and consideration must be given in planning to design features that
will make backfilling operations less difficult to accomplish. Examples of problem areas and
how forethought in design and planning can help to eliminate backfill deficiencies are
presented in the following paragraphs.
8-3.2.1 Effect of Excavation And Structural Configuration On Backfill Operations.
Some of the problems encountered in earthwork construction are related to the excavation and
the configuration of the structures around which backfill is to be placed. It is the designer’s
8-39

UFC 3-220-01N
15 AUGUST 2005
responsibility to recognize these problems and to take the necessary measures to minimize
their impact on the backfill operations.
8-3.2.1.1 Open Zones. An open zone is defined as a backfill area of sufficient dimensions
to permit the operation of heavy compaction equipment without endangering the integrity of
adjacent structures around which compacted backfill operations are conducted. Figure 8-3.1
shows examples of open zones. In these zones where large compaction equipment, can
operate, it is generally not too difficult to obtain the desired density if appropriate materials and
proper backfill procedures are used. For areas that can be economically compacted by heavy
equipment, the designer can avoid problems by including in the design provisions sufficient
working space between structures or between excavation slopes and structures to permit
access by the heavy compaction equipment. Generally, a working space of at least 3.6 m (12
ft) between structure walls and excavation slope and at least 4.5 m (15 ft) between structures
is necessary for heavy equipment to maneuver. In addition to maneuvering room, the designer
must also consider any adverse loading caused by the operation of heavy equipment too close
to structure walls, as discussed in paragraph 2-3d.
8-3.2.1.2 Confined zones. Confined zones are defined as areas where backfill operations
are restricted to the use of small mechanical compaction equipment (Fig 8-3.2) either because
the working room is limited or because heavy equipment (Fig. 8-3.1) would impose excessive
soil pressures that could damage the structure. Most deficiencies in compacted backfill around
subsurface structures have occurred in confined zones where required densities are difficult to
achieve because of restricted working room and relatively low compaction effort of equipment
that is too lightweight. The use of small equipment to achieve required compaction is also
more expensive than heavy equipment since thinner lifts are required. However, because
small compaction equipment can operate in spaces as narrow as 0.6 m (2 ft) in width, such
equipment is necessary to achieve the required densities in some areas of most backfill
projects. Therefore, the designer should plan structure and excavation areas to minimize the
use of small compaction equipment.
8-3.2.2 Structure Configuration. The designer familiar with backfilling operations can
avoid many problems associated with difficult to reach confined zones, which are created by
structural shapes obstructing the placement and compaction of backfill, by considering the
impact of structural shape on backfill operations. In most cases, structural shapes and
configurations that facilitate backfill operations can be used without significantly affecting the
intended use of the structure.
8-3.2.2.1 Curved Bottom and Wall Structures. Areas below the spring line of circular,
elliptical, and similar shaped structures are difficult to compact backfill against because
compaction equipment cannot get under the spring line. If possible, structures should be
designed with continuously curved walls and flat floors such as in an igloo-shaped structure.
For structures where a curved bottom is required to satisfy the intended function, it may be
advisable for the designer to specify that a template shaped like the bottom of the structure be
used to guide the excavation below the spring line so that uniform foundation support will be
provided.
8-40

UFC 3-220-01N
15 AUGUST 2005
8-3.2.2.2 Complex Structures. Complex structures have variable shaped walls and
complex configurations in plan and number of levels. These structures can also be simple
structures interconnected by access shafts, tunnels, and utility conduits. Because of their
irregular shapes and configurations the different types of structures significantly increase
excavation and backfill problems.
Typical examples of complex structures are stepped multilevel structures and
multichambered structures with interconnecting corridors (Figure 8-3.3). Complex structures
are generally more difficult to compact backfill around and are more likely to have settlement
problems (paragraph 8-3.2.3.1). Although the multilevel step structure (Figure 8-3.3(a)) is not
particularly difficult to compact backfill around, at least for the first level, the compaction of
backfill over the offset structure will generally require the use small equipment. Small
equipment will also be required for compaction of backfill around and over the access corridor
and between the two chambers (Figure 8-3.3 (b)). Where possible, the design should
accommodate intended functions into structures with uniformly shaped walls and a simple
configuration.
Where structures of complex configurations are necessary, construction of a
three-dimensional model during the design and planning phases will be extremely beneficial.
From the model, designers can more easily foresee and eliminate areas in which it would be
difficult to place and compact backfill.
8-3.2.2.3 Service Conduits. Since compaction of backfill is difficult around pipes and
conduits, group utility lines together or place in a single large conduit where feasible, rather
than allow to form a haphazard maze of pipes and conduits in the backfill. Run utility lines
either horizontally or vertically wherever possible. Coordinate plans for horizontally run
appurtenances, such as utility lines, access tunnels, and blast-delay tubing, with the
excavation plans so that wherever feasible these appurtenances can be supported by
undisturbed soils rather than by compacted backfill.
8-41

UFC 3-220-01N
15 AUGUST 2005
Figure 8-3.1 Open Backfill Zone
8-42

UFC 3-220-01N
15 AUGUST 2005
8-3.2.2.4 Excavation Plans. Develop excavation plans with the backfill operations and
the structure configurations in mind. The excavation and all completed structures within the
excavation should be conducive to good backfill construction procedures, and access should
be provided to all areas so that compaction equipment best suited to the size of the area can
be used. The plans for excavation should also provide for adequate haul roads and ramps.
Positive excavation slopes should be required in all types of soil deposits to facilitate
compaction of backfill against the slope and to ensure good bond between the backfill and the
excavation slopes. Remove loose material from the excavation slopes; in some case, benches
may be required to provide a firm surface to compact backfill against.
Figure 8-3.2 Confined Backfill Zones
8-43

UFC 3-220-01N
15 AUGUST 2005
Figure 8-3.3 Complex Structures
8-44

UFC 3-220-01N
15 AUGUST 2005
8-3.2.2.5 Lines and Grades. Exercise care in planning lines and grades for excavation to
ensure that uniform, adequate support is provided at the foundation level of important
structures. Generally, foundations consisting of part backfill and part undisturbed materials do
not provide uniform bearing and should be avoided wherever possible. The foundation should
be overexcavated where necessary and backfilled with compacted select material to provide
uniform support for the depth required for the particular structure. Where compacted backfill is
required beneath a structure, the minimum depth specified should be at least 450 mm (18
inches).
8-3.2.2.6 Thin-walled Metal Structures. Thin-walled, corrugated metal structures are
susceptible to deflections of structural walls when subjected to backfill loads. Minimize
adverse deflections by planning backfill operations so that compacted backfill is brought up
evenly on both sides of the structure to ensure uniform stress distribution. Temporary
surcharge loads applied to the structure crown may also be required to prevent vertical
distortions and inward deflection at the sides.
8-3.2.3 Backfill Problem Areas. Other features that have the potential to become
problem areas are discussed in the following paragraphs. These potential problem areas must
be considered during the planning and design phases to minimize deficiencies in structure
performance associated with backfill placement and to make backfilling operations less
difficult.
8-3.2.3.1 Settlement and Downdrag. In the construction of underground structures and
particularly missile launch site facilities, tolerances to movement are often considerably less
than those in normal construction. The design engineer must determine and specify allowable
tolerances in differential settlement and ensure that differential settlement is minimized and/or
accommodated. Settlement analysis procedures are outlined in Chapter 4.
8-3.2.3.2 Critical Zones. Critical backfill zones are those immediately beneath most
structures. Consolidation and swelling characteristics of backfill materials should be
thoroughly investigated so that materials having unfavorable characteristics will not be used in
those zones. Some settlement can be expected to take place, but it can be minimized by
requiring a higher than normal compacted density for the backfill. Cohesive backfill compacted
at water content as little as 3 to 4 percentage points below optimum may result in large
settlements caused by collapse of non-swelling soil material or heave of swelling materials
upon saturation after construction. Compacting cohesive backfill material at optimum water
content or slightly on the wet side of optimum generally will reduce the amount of settlement
and swelling that would occur. Confirm the reduction by consolidation and swell tests on
compacted specimens.
8-3.2.3.3 Service Conduits. Settlement within the backfill around structures will also
occur. A proper design will allow for the estimated settlement as determined from studies of
consolidation characteristics of the compacted backfill. Where service conduits, access
corridors, and similar facilities connect to the structure oversize sleeves, flexible connections
and other protective measures, as appropriate, may be used to prevent damage within the
8-45

UFC 3-220-01N
15 AUGUST 2005
structure.
8-3.2.3.4 Differential Settlement. Complex structures are more susceptible to differential
settlement because of the potential for large variations in loads carried by each component
foundation. In the multilevel stepped structure (Figure 8-3.3 (a)), the foundation supporting the
lower level offset component must also support the volume of backfill over that part of the
structure. Measures must be taken to ensure that the proper functioning of all elements is not
hampered by differential settlement. The increased cost of proper design and construction
where unusual or difficult construction procedures are required is insignificant when compared
with the cost of the structure. The cost of remedial measures to correct deficiencies caused by
improper design and construction usually will be greater than the initial cost required to prevent
the deficiencies.
8-3.2.3.5 Downdrag. In addition to conventional service loads, cut and cover subsurface
structures are susceptible to downdrag frictional forces between the structure and the backfill
that are caused by settlement of the backfill material adjacent to and around the structure.
Downdrag loads can be a significant proportion of the total vertical load acting on the structure
and must be considered in the structure settlement analysis. Structure-backfill friction forces
may also generate significant shear forces along the outer surface of structures with
curve-shaped roofs and walls. The magnitude of the friction forces depends upon the type of
backfill, roughness of the structure's surface, and magnitude of earth pressures acting against
the structure. Techniques for minimizing downdrag friction forces generally include methods
that reduce the structure surface roughness such as coating the structure's outer surface with
asphalt or sandwiching a layer of polyethylene sheeting between the structure's outer surface
and fiberboard (blackboard) panels. Backfill settlement and associated downdrag can also be
minimized by requiring higher backfill densities adjacent to the structure.
Figure 8-3.4 Excavation Subject to Bottom Heave
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Figure 8-3.5 Excess Lateral Pressure Against Vertical Walls Induced by Compaction
8-3.2.3.6 Groundwater. Groundwater is an important consideration in planning for
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construction of subsurface structures. If seepage of groundwater into the excavation is not
adequately controlled, backfilling operations will be extremely difficult. The groundwater level
must be lowered sufficiently (at least 0.6 – 0.9 m (2 to 3 ft) for granular soils and as much as
1.6 - 3 m (5 to 10 ft) for fine-grained soils below the lowest level of backfilling) so that a firm
foundation for backfill can be established. If the level is not lowered, the movement of hauling
or compaction equipment may pump seepage water through the backfill, or the initial backfill
layers may be difficult to compact because of an unstable foundation. Since the proper water
content of the backfill is essential for achieving proper compaction, prevention of groundwater
seepage into the excavation during backfilling operations is mandatory.
• The contractor is generally responsible for the design, installation, and operation
of dewatering equipment. Inadequate dewatering efforts can be minimized by
adequate planning and implementation of groundwater investigations
• The possibility of hydraulic heave in cohesive material must also be investigated
to ensure stability of the excavation floor. Hydraulic heave may occur where an
excavation overlies a confined permeable stratum below the groundwater table
8-3.3a. If the upward hydrostatic pressure acting at the bottom of the confining
layer exceeds the weight of overburden between the bottom of the excavation
and the confining layer, the bottom of the excavation will rise bodily even though
the design of the dewatering system is adequate for control of groundwater into
the excavation. To prevent heave, the hydrostatic pressure beneath the confined
stratum must be relieved
• Subsurface structures located in part or wholly below the groundwater table
require permanent protection against groundwater seepage. The type of
protection may range from simple impermeable barriers to complex permanent
dewatering systems
• Dewatering and groundwater control procedures are described in Chapter 9
8-3.2.3.7 Gradation and Filter Criteria for Drainage Materials. Groundwater control is
often accomplished by ditches positioned to intercept the flow of groundwater and filled with
permeable granular material. The water is generally collected in perforated pipes located at
the bottom of the ditch and pumped to a suitable discharge area. Such drainage systems are
referred to as filter drains. The gradation of the granular filter material is critical for the
functioning of the system. Selection of the proper gradation for the filter material is dependent
upon the gradation of the material that is being drained. Drainage of silts and clays usually re-
quires a graded filter made up of several layers of granular material with each layer having
specific requirements for maximum grain size and gradation. Details on the design of filter
drains are presented in Chapter 9.
8-3.2.3.7.1 Selected Material. If materials at the jobsite do not meet the designed filter
requirements, select material must be purchased from commercial sources and shipped to the
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jobsite. Filter material must be stockpiled according to gradation. For graded filter systems,
the materials must be placed with care to minimize mixing of individual components.
8-3.2.3.7.2 Filter Cloths. Both woven and non-woven filter cloths, which have been found
satisfactory for use as a filter media for subsurface drains, are available. When granular filter
materials are not economically available, a single wrap of filter cloth around a pipe may be
used in lieu of a coarser backfill. When available granular filter material is too coarse to satisfy
filter criteria for the protected soil, a single layer of filter cloth may be used adjacent to the
protected soil. To reduce the chance of clogging, no filter cloth should be specified with an
open area less than 4 percent and or equivalent opening size (EOS) of less than the No. 100
sieve (0.15 mm (0.0059 inch)). A cloth with openings as large as allowable should be
specified to permit drainage and prevent clogging. Additional information on air- field drainage
is contained in TM 5-820-2/AFM 88-5.
Filter cloth can also provide protection for excavated slopes and serve as a filter
to prevent piping of fine-grained soils. In one project, sand was not available for backfill behind
a wall and coarse gravel had to be used to collect seepage. The filter cloth used to protect the
excavated slope served as a filter against piping of the natural silty clay under seepage
gradients out of the excavated slope after the coarse gavel backfill was placed.
8-3.2.3.8 Earth Pressures. The rationale design of any structure requires the designer to
consider all loads acting on the structure. In addition to normal earth pressures associated
with the effective pressure distribution of the backfill materials, subsurface cut-and- cover
structures may also be subjected to surcharge loads caused by heavy equipment operating
close to the structure and by increased permanent lateral earth pressures caused by
compaction of backfill material with heavy equipment. Procedures for predicting normal earth
pressures associated with the effective pressure of backfill materials are discussed in Chapter
6.
8-3.2.3.8.1 Surcharge Earth Pressures. Exact solutions for surcharge earth pressures
generated by heavy equipment (or other surcharge loads) do not exist. However,
approximations can be made using appropriate theories of elasticity such as Boussinesq's
equations for load areas of regular shape or Newmark's charts for irregular shaped load areas
as given in UFC 3-220-10N. As a conservative guide, heavy-equipment surcharge earth
pressures may be minimized by specifying that heavy compaction equipment maintain a
horizontal distance from the structure equivalent to the height of the backfill above the
structure's foundation.
8-3.2.3.8.2 Compaction Induced Pressures. Compaction-induced earth pressures can
cause a significant increase in the permanent lateral earth pressures acting on a vertical wall
of a structure (fig. 8-3.5). This diagram is based on the assumption that the equipment can
operate to within 150 mm (6 in) of the wall. Significant reductions in lateral pressures occur as
the closest allowable distance to the wall is increased (Fig 8-3.5). For an operating distance
1.5 m (5 ft) from the wall, the induced horizontal earth pressure is much less than that caused
by the backfill. The magnitude of the increase in lateral pressure is dependent, among other
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factors, on the effective weight of the compaction equipment and the weight, earth pressure
coefficient, and Poisson's ratio of the backfill material. Compaction-induced earth pressures
against walls are also described in Chapter 6.
The designer must evaluate the economics of the extra cost of structures
designed to withstand very close-in operation of heavy compaction equipment versus the extra
cost associated with obtaining required compaction of backfill in thin lifts with smaller
compaction equipment. A more economical alternative might be to specify how close to the
walls different weights of compaction equipment can be operated.
One method of reducing lateral earth pressures behind walls has been to use
about 1.2 m (4 ft) of uncompacted granular (sand or gravel) backfill above the base of the wall.
Soil backfill can then be compacted in layers above the granular backfill. Compression of the
granular material prevents the buildup of excessive lateral pressures against the wall.
8-3.3 Evaluation, Design, and Processing of Backfill Materials. The evaluation,
design, and proper processing of backfill materials are extremely important phases of the pre-
construction operations. The purpose of the evaluation phase is to determine the engineering
characteristics of potential backfill materials. The design phase must take into account the
engineering characteristics required of the backfill and specify materials that, when compacted
properly, will have these characteristics. Proper processing of the backfill material will ensure
that desirable engineering characteristics will be obtained as the material is placed.
8-3.3.2 Evaluation of Backfill Materials. Evaluation of backfill materials consists of
exploration, sampling, and laboratory testing to determine the engineering characteristics of
potential backfill materials. Detailed instructions for exploration, sampling, laboratory testing,
and foundation design are presented in Chapters 2 and 3. However, to emphasize the need
for an adequate investigation, some aspects of planning and investigation that should be
considered are discussed in the following paragraphs.
8-3.3.2.1 Field Exploration and Sampling. Field exploration and sampling are extremely
important to the design of foundations, selection of backfill, and planning for construction. A
great amount of material will be available from required excavations, and the investigation for
foundation conditions should include the sampling and evaluation of these materials for
possible use as backfill. Where an adequate volume of suitable backfill cannot be obtained
from the construction excavation, the exploration and sampling program must be expanded to
find other sources of suitable material whether from nearby borrow areas or commercial
sources.
The purpose of the investigation is to delineate critical conditions and provide
detailed information on the subsurface deposits so that proper design and construction,
including backfilling operations, can be accomplished with minimum difficulty. Thus careful
planning is required prior to the field exploration and sampling phase of the investigation.
Available geologic and soil data should be studied, and if possible, preliminary borings should
be made. Once a site has been tentatively selected, orientation of the structure to the site
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should be established. The engineer who plans the detailed field exploration program must
have knowledge of the structure, e.g., its configuration and foundation requirements for design
loads and settlement tolerances. The planning engineer should also know the type and
quantity of backfill required. The importance of employing qualified field exploration personnel
cannot be overemphasized. The exploration crews should be supervised in the field by a soils
engineer or geologist familiar with the foundation and backfill requirements so that changes
can be made in the exploration program where necessary to provide adequate information on
subsurface conditions. The field engineer should also know the location of significant features
of the structure so that sampling can be concentrated at these locations. In addition, he should
have an understanding of the engineering characteristics of subsurface soil and rock deposits
that are important to the design of the structure and a general knowledge of the testing
program so that the proper type and quantity of samples will be obtained for testing.
• From the samples, the subsurface deposits can be classified and boring logs
prepared. The more continuous the sampling operation, the more accurate will
be the boring logs. All borings should be logged with the description of the
various strata encountered as discussed in ASTM D 1586 and ASTM D 2487.
Accurate logging and correct evaluation of all pertinent information are essential
for a true concept of subsurface conditions.
• When the exploratory borings at the construction site have been completed, the
samples and logs of borings should be examined to determine if the material to
be excavated will be satisfactory and in sufficient quantity to meet backfill
requirements. Every effort should be made to use the excavated materials; how-
ever, if the excavated materials are not satisfactory or are of insufficient quantity,
additional exploration should be initiated to locate suitable borrow areas. If
borrow areas are not available, convenient commercial sources of suitable
material should be found. Backfill sources, whether excavation, borrow, or
commercial, should contain several times the required volume of compacted
backfill.
• Groundwater studies prior to construction of subsurface structures are of the
utmost importance, since groundwater control is necessary to provide a dry
excavation in which construction and backfilling operations can be properly
conducted. Data on groundwater conditions are also essential for forecasting
construction dewatering requirements and stability problems. Groundwater
studies must consist of investigations to determine: groundwater levels to include
any seasonal variations and artesian conditions; the location of any
water-bearing strata; and the permeability and flow characteristics of
water-bearing strata. Methods for investigating groundwater conditions are
described in Chapter 9.
8-3.3.2.2 Laboratory Testing. The design of any foundation is dependent on the
engineering characteristics of the supporting media, which may be soil or rock in either its
natural state or as compacted backfill. The laboratory-testing program will furnish the engineer
information for planning, designing, and constructing subsurface structures. Laboratory testing
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programs usually follow a general pattern and to some extent can be standardized, but they
should be adapted to particular problems and soil conditions. Special tests and research
should be utilized when necessary to develop needed information. The testing program should
be well planned with the engineering features of the structure and backfill in mind; testing
should be concentrated on samples from areas where significant features will be located but
should still present a complete picture of the soil and rock properties. The laboratory test
procedures and equipment are described in ASTM D 2487 and its references.
8-3.3.2.2.1 Identification and Classification of Soils. The Unified Soil Classification
System used for classifying soils for military projects (ASTM D 2487) is a means of identifying
a soil and placing it in a category of distinctive engineering properties. Table 8-3.1 shows the
properties of soil groups pertinent to backfill and foundations. Using these characteristics, the
engineer can prepare preliminary designs based on classification and plan the laboratory
testing program intelligently and economically.
The Unified Soil Classification System classifies soils according to their grain-
size distribution and plasticity characteristics and groups them with respect to their engineering
behavior. With experience, the plasticity and gradation properties can be estimated using
simple, expedient tests (See ASTM D 2487) and these estimates can be confirmed using
simple laboratory tests. The principal laboratory tests performed for classification are
grain-size analyses and Atterberg limits.
The engineering properties in table 8-3.1 are based on "Standard Proctor"
(ASTM D 2487) maximum density except that the California Bearing Ratio (ASTM D 1883) and
the subgrade modulus are based on ASTM D 1557 maximum density. This information can be
used for initial design studies. However, for final design of important structures, laboratory
tests are required to determine actual performance characteristics, such as ASTM D 1557
compaction properties, shear strength, permeability, compressibility, swelling characteristics,
and frost susceptibility where applicable, under expected construction conditions.
The Unified Soil Classification System is particularly useful in evaluating, by
visual examination, the suitability of potential borrow materials for use as compacted backfill.
Proficiency in visual classification can be developed through practice by comparing estimated
soil properties with results of laboratory classification tests.
8-3.3.2.2.2 Compaction Testing. Compaction test procedures are described in detail in
ASTM D 1557 (app. A.) It is important that the designer and field inspection personnel
understand the basic principles and fundamentals of soil compaction. The principles of soil
compaction are discussed in appendix B of this manual.
The purpose of the laboratory compaction tests is to determine the compaction
characteristics of available backfill materials. Also, anticipated field density and water content
can be approximated in laboratory compacted samples in order that other engineering
properties, such as shear strength, compressibility, consolidation, and swelling, can be
studied. For most soils there is an optimum water content at which a maximum density is
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8-53
obtained with a particular compaction effort. A standard five-point compaction curve relating
density and water content can be developed by the procedures outlined in ASTM D 1557.
The impact compaction test results normally constitute the basis on which field
compaction control criteria are developed for inclusion in the specifications. However, for
some cohesionless soils, higher densities can be obtained by the vibratory compaction method
(commonly referred to as maximum relative density), described in EM 1110-21906. The
required field compaction is generally specified as a percentage of laboratory maximum dry
density and referred to as percent ASTM D 1557 maximum density. Water content is an
important controlling factor in obtaining proper compaction. The required percentage of
maximum dry density and the compaction water content should be selected on the basis of the
engineering characteristics, such as compression moduli, settlement, and shear strength,
desired in the compacted backfill. It should be noted that these characteristics could be
adversely affected by subsequent increases in water content after placement. This situation
could result from an increase in the groundwater level after construction.
Density control of placed backfill in the field can be facilitated by the use of rapid
compaction check tests (ASTM D 5080). A direct rapid test is the one-point impact compaction
test. Rapid indirect tests, such as the Proctor needle penetration for cohesive soils or the cone
resistance load for cohesionless soils, can also be used when correlations with ASTM D 1557
maximum density have been established.

Table 8-3.1 Typical Engineering Properties of Compacted Materialsa
Typical Value of
Compression
(Percent of
Original Height) Typical Strength Characteristics
Group
Symbol
Soil Type
Range of
Maximum
Dry Unit
Weight,
gm/cm3
(pcf)
Range of
Optimum
Water,
Content
Percent
At 138
kPa
(20
psi)
At 345
kPa
(50 psi)
Cohesion
(as
compacted)
psf
Cohesion
(saturated)
psf
Effective
Stress
Envelope
deg
Typical
Coefficient
of
Permeability
cm/sec
(ft/min)
Range of
CBR
Values
Range of
Subgrade
Modulus k
kPa/mm
(lb/cu in)
GW Well
graded,clean
gravels,
gravel-sand
mixtures
2.00-2.16
(125-135)
11-8 0.3 0.6 0 0 >38 2.5 x 10-2
(5x10-2
)
40-80 81-136
(300-500)
GP Poorly
graded clean
gravel-sand
mix
1.84-2.00
(115-125)
14-11 0.4 0.9 0 0 >37 5 x 10-2
(10-1
)
30-60 68-108
(250-400)
GM Silty gravels,
poorly graded
gravel-sand-
silt
1.92-2.16
(120-135)
12-8 0.5 1.1 ----- ----- >34 >5 x 10-7
(>10-6
)
20-60 27-108
(100-400)
GC Clayey
gravels,
poorly graded
gravel-sand-
clay
1.84-2.08
(115-130)
14-9 0.7 1.6 ----- ----- >31 >5 x 10-8
(>10-7
)
20-40 27-81
(100-300)
SW Well graded
clean sands,
gravelly
sands
1.76-2.08
(110-130)
16-9 0.6 1.2 0 0 38 5 x 10-4
(>10-3
)
20-40 54-81
(200-300)

Typical Value of
Compression
(Percent of
Group
Symbol
Soil Type
Range of
Maximum
Dry Unit
Weight,
gm/cm3
(pcf)
Range of
Optimum
Water,
Content
Percent
At 138
kPa
(20 psi)
At 345
kPa
(50
psi)
Cohesion
(as
compacted)
kPa (psf)
Cohesion
(saturated)
kPa (psf)
Effective
Stress
Envelope
deg
Typical
Coefficient
of
Permeability
cm/sec
(ft/min)
Range
of CBR
Values
Range of
Subgrade
Modulus k
kPa/mm
(lb/cu in)
SM Silty sands,
poorly
graded
sand-salt
mix
1.76-2.00
(110-125)
16-11 0.8 1.6 50 (1050) 20 (420) 34 2.5 x 10-5
(5 x 10-5
)
10-40 21-81
(100-300)
SM-SC Sand-silt
clay mix
with slightly
plastic fines
1.76-2.08
(110-130)
15-11 0.8 1.4 50 (1050) 14 (300) 33 1 x 10-6
(2x10-6
)
----- ------
SC Clayey
sands,
poorly
graded
sand-clay-
mix
1.68-2.00
(105-125)
19-11 1.1 2.2 74 (1550) 11 (230) 31 2.5 x 10-7
(5x10-7
)
5-20 21-81
(100-300)
ML Inorganic
silts and
clayey silts
1.52-1.92
(95-120)
24-12 0.9 1.7 67 (1400) 9 (190) 32 5 x 10-6
(10-5
)
15 or < 21-54
(100-200)
ML-CL Mixture of
inorganic silt
and clay
1.60-1.92
(100-200)
22-12 1.0 2.2 65 (1350) 22 (460) 32 2.5 x 10-5
(5x10-5
)
----- 21-54
(100-200)

Typical Value of
Compression
(Percent of
Group
Symbol
Soil Type
Range of
Maximum
Dry Unit
Weight,
gm/cm3
(pcf)
Range of
Optimum
Water,
Content
Percent
At 138
kPa
(20
psi)
At 345
kPa
(50 psi)
Cohesion
(as
compacted)
kPa (psf)
Cohesion
(saturated)
kPa (psf)
Effective
Stress
Envelope
deg
Typical
Coefficient
of
Permeability
cm/sec
(ft/min)
Range of
CBR
Values
Range of
Subgrade
Modulus k
kPa/mm
(lb/cu in)
CL Inorganic
clays of low
to medium
plasticity
1.52-1.92
(95-120)
34-12 1.3 2.5 86 (1800) 13 (270) 28 5 x 10-8
(10-7
)
15 or < 14-54
(50-200)
OL Organic silts
and silt-clays
of low
plasticity
1.28-1.60
(80-100)
33-21 ----- ----- ----- ----- ----- ----- 5 or < 14-27 (50-
100)
MH Inorganic
clayey silts,
elastic silts
1.20-1.52
(75-95)
40-24 2.0 3.8 72 (1500) 20 (420) 25 2.5 x 10-7
(5x10-7
)
10 or < 14-27
(50-100)
CH Inorganic
clays of high
plasticity
1.28-1.68
(80-105)
36-19 2.6 3.9 103 (2150) 11 (230) 19 5 x 10-8
(10-7
)
15 or < 14-34
(50-150)
OH Organic and
silty clays
1.20-1.60
(75-100)
45-21 ----- ----- ----- ----- ----- ----- 5 or < 7-27
(25-100)
Notes: 1. All properties are for condition of Standard Proctor maximum density except values of k and CBR, which are for CE55 maximum density.
2. Typical strength characteristics are for effective strength envelopes and are obtained from USBR data.
3. Compression values are for vertical loading with complete lateral reinforcement.
4. (>) Indicates that typical property is greater than the value shown. (…..) Indicates insufficient data available for an estimate.

UFC 3-220-01N
15 AUGUST 2005
8-3.3.2.2.3 Shear Strength Testing. When backfill is to be placed behind structure walls or
bulkheads or as foundation support for a structure, and when fills are to be placed with
unrestrained slopes, shear tests should be performed on representative samples of the backfill
materials compacted to expected field densities and water contents to estimate as constructed
shear strengths. The appropriate type of test required for the conditions to be analyzed is
presented in ASTM D 3080, 6528 and 4767. Procedures for shear strength testing are
described in EM 1110-2-1906.
8-3.3.2.2.4 Consolidation and Swell Testing. The rate and magnitude of consolidation
under a given load are influenced primarily by the density and type of soil and the conditions of
saturation and drainage. Fine-grained soils generally consolidate more and at a slower rate
than coarse-grained soils. However, poorly graded, granular soils and granular soils
composed of rounded particles will often consolidate significantly under load but usually at a
relatively fast rate.
The procedure for the consolidation test is outlined in ASTM D 2435 and D 4546.
The information obtained in this test can be used in settlement analyses to determine the total
settlement, the time rate of settlement, and the differential settlement under varying loading
conditions. Consolidation characteristics are important considerations in selection of backfill
materials. The results of consolidation tests performed on laboratory compacted specimens of
backfill material can be used in determining the percent compaction to be required in the
specifications.
Swelling characteristics can be determined by a modified consolidation test
procedure. The degree of swelling and swelling pressure should be determined on all backfill
and foundation materials suspected of having swelling characteristics. This fact is particularly
important when a considerable overburden load is removed by excavation or when the
compacted backfill with swelling tendencies may become saturated upon removal of the
dewatering system and subsequent rise of the groundwater level. The results of swelling tests
can be used to determine the suitability of material as backfill. When it is necessary to use
backfill materials that have a tendency to swell upon saturation because more suitable
materials are unavailable, the placement water content and density that will minimize swelling
can be determined from a series of tests. FHWA-RD-79-51 provides further information
applicable to compacted backfills.
8-3.3.2.2.5 Permeability Tests. Permeability tests to determine the rate of flow of water
through a material can be conducted in the laboratory by procedures described in ASTM D
2434, D 2335 and D 3152. Permeability characteristics of fine-grained materials at various
densities can also be determined from consolidation tests.
Permeability characteristics for the design D3 of permanent drainage systems for
structures founded below the groundwater level must be obtained from laboratory tests. The
tests should be performed on representative specimens of backfill materials compacted in the
laboratory to densities expected in the field.
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8-3.4.4.3 Rock. The suitability of rock as backfill material is highly dependent upon the
gradation and hardness of the rock particles. The quantity of hard rock excavated at most
subsurface structure sites is relatively small, but select cohesionless materials may be difficult
to find or may be expensive. Therefore, excavated hard rock may be specified for crusher
processing and used as select cohesionless material.
8-3.4.4.4 Shale. Although shale is commonly referred to as rock, the tendency of some
shales to breakdown under heavy compaction equipment and slake when exposed to air or
water after placement warrants special consideration.
Some soft shales break down under heavy compaction equipment causing the
material to have entirely different properties after compaction than it had before compaction.
This fact should be recognized before this type of material is used for backfill. Establishing the
proper compaction criteria may require that the contractor construct a test fill and vary the
water content, lift thickness, and number of coverages with the equipment proposed for use in
the backfill operation. This type of backfill can be used only in unrestricted open zones where
heavy towed or self-propelled equipment can operate.
Some shales have a tendency to break down or slake when exposed to air.
Other shales that appear rock-like when excavated will soften or slake and deteriorate upon
wetting after placement as rockfill. Alternate cycles of wetting and drying increases the slaking
process. The extent of material breakdown determines the manner in which it is treated as a
backfill material. If the material completely degrades into constituent particles or small chips
and flakes, it must be treated as a soil-like material with property characteristics similar to ML,
CL, or CH materials, depending upon the intact composition of the parent material. Complete
degradation can be facilitated by alternately wetting, drying, and disking the material before
compaction. A detailed discussion on the treatment of shales as a fill material is given in
FHWA-RD-78-141.
8-3.4.4.5 Marginal Materials. Marginal materials are those materials that, because of
either poor compaction, consolidation, or swelling characteristics, would not normally be used
as backfill if sources of suitable material were available. Material considered to be marginal
include fine-grained soils of high plasticity and expansive clays. The decision to use marginal
materials should be based on economical and energy conservation considerations to include
the cost of obtaining suitable material whether from a distant borrow area or commercial
sources, possible distress repair costs caused by use of marginal material, and the extra costs
involved in processing, placing, and adequately compacting marginal material.
The fine-grained, highly plastic materials make poor backfill because of the
difficulty in handling, exercising water-content control, and compacting. The water content of
highly plastic finegrained soils is critical to proper compaction and is very difficult to control in
the field by aeration or wetting. Furthermore, such soils are much more compressible than
less-plastic and coarse-grained soils; shear strength and thus earth pressures may fluctuate
between wide limits with changes in water content; and in cold climates, frost action will occur
in fine-grained soils that are not properly drained. The only soil type in this category that might
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be considered suitable as backfill is inorganic clay (CH). Use of CH soils should be avoided in
confined areas if a high degree of compaction is needed to minimize backfill settlement or to
provide a high compression modulus.
The swelling (and shrinking) characteristics of expansive clay vary with the type
of clay mineral present in the soil, the percentage of that clay mineral, and the change in water
content. The active clay minerals include montmorillonite, mixed-layer combinations of
montmorillonite and other clay minerals, and under some conditions chlorites and vermiculites.
Problems may occur from the rise of groundwater, seepage, leakage, or elimination of surface
evaporation that may increase or decrease the water content of compacted soil and lead to the
tendency to expand or shrink. If the swelling pressure developed is greater than the
restraining pressure, heave will occur and may cause structural distress. Compaction on the
wet side of optimum moisture content will produce lower magnitudes of swelling and swell
pressure. Expansive clays that exhibit significant volume increases should not be used as
backfill where the potential for structural damage might exist. Suitability should be based upon
laboratory swell tests.
Additives, such as hydrated lime, quicklime, and fly ash, can be mixed with some
highly plastic clays to improve their engineering characteristics and permit the use of some
materials that would otherwise be unacceptable. Hydrated lime can also be mixed with some
expansive clays to reduce their swelling characteristics. Laboratory tests should be performed
to determine the amount of the additive that should be used and the characteristics of the
backfill material as a result of using the additive. Because of the complexity of soil additive
systems and the almost completely empirical nature of the current state of the art, trial mixes
must be verified in the field by test fills.
8-3.4.4.6 Commercial By-Products. The use of commercial by-products, such as
furnace slag or fly ash as backfill material, may be advantageous where such products are
locally available and where suitable natural materials cannot be found. Fly ash has been used
as a lightweight backfill behind a 7.6 m (25 ft) high wall and as an additive to highly plastic
clay. The suitability of these materials will depend upon the desirable characteristics of the
backfill and the engineering characteristics of the products.
8-3.5 Processing of Backfill Materials. The construction of subsurface structures
often requires the construction of elements of the structure within or upon large masses of
backfill. The proper functioning of these elements is often critically affected by adverse
behavioral characteristics of the backfill. Behavioral characteristics are related to material
type, water content during compaction, gradation, and compaction effort. While compaction
effort may be easily controlled during compaction, it is difficult to control material type, water
content, and gradation of the material as it is being placed in the backfill; control criteria must
be established prior to placement.
8-3.5.1 Material Type. Backfill material should consist of a homogeneous material of
consistent and desirable characteristics. The field engineer must ensure that only the
approved backfill material is used and that the material is uniform in nature and free of any
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anomalous material such as organic matter or clay pockets. Stratified material should be
mixed prior to placing to obtain a uniform blend. Stockpile excavated material to be used as
backfill according to class or type of material.
8-3.3.5.2 Water Content. While water content can be adjusted to some extent after
placing (but before compacting), it is generally more advantageous to adjust the water content
to optimum compaction conditions before placing. Adjustment of water content can be
accomplished by aeriation (disking or turning) or sprinkling the material in 305 mm to 450 mm
(12 to 18 in) layers prior to placing or stockpiling. If the material is stockpiled, provisions
should be made to maintain constant moisture content during wet or dry seasons.
8-3.3.5.3 Ensuring Gradation. Some backfill materials consisting of crushed rock, gravel,
or sand require limitations on maximum and minimum particle-size or gradation distributions.
Where materials cannot be located that meet gradation criteria, it may be advantageous to
require processing of available material by sieving to obtain the desired gradation.
8-4 EARTHWORK: EXCAVATION AND PREPARATION FOR FOUNDATIONS
8-4.1 Excavation
8-4.1.1 General. In general, excavation for subsurface structures will consist of open
excavation and shaft and tunnel excavation. Where excavation to great depths is required, a
variety of soils and rock may be encountered at a single site. Soils may range through a wide
spectrum of textures and water contents. Rock encountered may vary from soft rock, very
similar to a firm soil in its excavation requirements, to extremely hard rock requiring extensive
blasting operations for removal. Groundwater may or may not be present. The groundwater
conditions and the adequacy of groundwater control measures are important factors in
excavation, in maintaining a stable foundation, and in backfilling operations. The extent to
which groundwater can be controlled also influences the slopes to which the open excavation
can be cut, the bracing required to support shaft and tunnel excavation, and the handling of the
excavated material.
8-4.1.2 Good Construction Practices, and Problems. A majority of the problems
encountered during excavation are related to groundwater conditions, slope stability, and
adverse weather conditions. Many of the problems can be anticipated and avoided by
preconstruction planning and by following sound construction practices.
8-4.1.2.1 Groundwater. Probably the greatest source of problems in excavation
operations is groundwater. If the seepage of groundwater into an excavation is adequately
controlled, other problems will generally be minor and can be easily handled. Several points
should be recognized that, if kept in mind, will help to reduce problems attributable to
groundwater. In some instances, groundwater conditions can be more severe than indicated
by the original field exploration investigation since field explorations provide information only
for selected locations and may not provide a true picture of the overall conditions.
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If groundwater seepage begins to exceed the capacity of the dewatering system,
conditions should not be expected to improve unless the increased flow is known to be caused
by a short-term condition such as heavy rain in the area. If seepage into the excavation
becomes excessive, excavation operations should be halted until the necessary corrective
measures are determined and affected. The design and evaluation of dewatering systems
require considerable experience that the contractor or the contracting office often do not
possess, and the assistance of specialists in this field should be obtained.
Groundwater without significant seepage flow can also be a problem since
excess hydrostatic pressures can develop below relatively impervious strata and cause uplift
and subsequent foundation or slope instability. Excess hydrostatic pressures can also occur
behind sheet pile retaining walls and shoring and bracing in shaft and tunnel excavations.
Visual observations should be made for indications of trouble, such as uncontrolled seepage
flow, piping of material from the foundation or slope, development of soft wet areas, uplift of
ground surface, or lateral movements.
Accurate daily records should be kept of the quantity of water removed by the
dewatering system and of the piezometric levels in the foundation and beneath excavation
slopes. Separate records should be kept of the flow pumped by any sump-pump system
required to augment the regular dewatering system to note any increase of flow into the
excavation. Flowmeters or other measuring devices should be installed on the discharge of
these systems for measurement purposes. These records can be invaluable in evaluating
"Changed Condition" claims submitted by the contractor. The contractor should be required to
have "standby" equipment in case the original equipment breaks down.
8-4.1.2.2 Surface Water. Sources of water problems other than groundwater are surface
runoff into the excavation and snow drifting into the excavation. A peripheral, surface-drainage
system, such as a ditch and berm, should be required to collect surface water and divert it from
the excavation. In good weather there is a tendency for the contractor to become lax in
maintaining this system and for the inspection personnel to become lax in enforcing
maintenance. The result can be a sudden filling of the excavation with water during a heavy
rain and consequent delay in construction. The surface drainage system must be constantly
maintained until the backfill is complete. Drifting snow is a seasonal and regional problem,
which can best be controlled by snow fences placed at strategic locations around the
excavation.
8-4.1.2.3 Slope Integrity. Another area of concern during excavation is the integrity of the
excavation slopes. The slopes may be either unsupported or supported by shoring and
bracing. The lines and grades indicated in the plans should be strictly adhered to. The
contractor may attempt to gain additional working room in the bottom of the excavation by
steepening the slopes; this change in the plans must not be allowed.
• Where shoring and bracing are necessary to provide a stable excavation, and the
plans and specifications do not provide details of these requirements, the
contractor should be required to submit the plans in sufficient detail so that they
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can be easily followed and their adequacy checked. The first principle of
excavation stabilization, using shoring and bracing, is that the placing of supports
should proceed with excavation. The excavation cut should not be allowed to
yield prior to placing of shoring and bracing since the lateral pressures to be
supported would generally be considerably greater after yield of the unshored cut
face than if no movement had occurred prior to placement of the shoring.
Excavation support systems are discussed in paragraph 8-1. All safety
requirements for shoring and bracing as contained therein and should be strictly
enforced.
• The inspector must be familiar with stockpiling requirements regarding the
distance from the crest of the excavation at which stockpiles can be established
and heavy equipment operated without endangering the stability of the
excavation slopes. He must also know the maximum height of stockpile or
weight of equipment that can be allowed at this distance.
• Excessive erosion of the excavation slopes must not be permitted. In areas
subject to heavy rainfall, it may be necessary to protect excavation slopes with
polyethylene sheeting, straw, silt fences, or by other means to prevent erosion.
Excavation slopes for large projects that will be exposed for several seasons
should be vegetated and maintained to prevent erosion.
8-4.1.2.4 Stockpiling Excavated Material. Generally, procedures for stockpiling are left
to the discretion of the contractor. Prior to construction, the contractor must submit his plans
for stockpiling to the contracting officer for approval. In certain cases, such as where there are
different contractors for the excavation and the backfill phases, it may be necessary to include
the details for stockpiling operations in the specifications. In either case, it is important that the
stockpiling procedures be conducive to the most advantageous use of the excavated
materials.
As the materials are excavated, they should be separated into classes of backfill
and stockpiled accordingly. Thus the inspection personnel controlling the excavation should
be qualified to classify the material and should be thoroughly familiar with backfill
requirements. Also, as the materials are placed in stockpiles, water should be added or the
materials should be aerated as required to approximate optimum water content for
compaction. Field laboratory personnel can assist in determining the extent to which this is
necessary. The requirements of shaping the stockpile to drain and sealing it against the
entrance of undesirable water by rolling with spreading equipment or covering with
polyethylene sheeting should be enforced. This step is particularly important for cohesive soils
that exhibit poor draining characteristics and tend to remain wet if once saturated by rains.
Stockpiles must be located over an area that is large enough to permit processing and where
they will not interfere with peripheral drainage around the excavation and will not overload the
slopes of the excavation.
In cases where significant energy and cost saving can be realized, special
stockpiling requirements should be implemented. An example would be a large project
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consisting of a number of excavation and backfilling operations. The excavation material from
the first excavation could be stockpiled for use as backfill in the last excavation. The material
from the intermediate excavations could in turn be immediately used as backfill for the first,
second, etc., phases of the project and thereby eliminate double handing of excavated backfill
for all but the first-phase excavation.
8-4.1.2.5 Protection of Exposed Material. If materials that are exposed in areas, such as
walls of a silo shaft, foundation support, or any other area against which concrete will be
placed, are susceptible to deterioration or swell when exposed to the weather, they should be
properly protected as soon after exposure as possible. Depending on the material and
protection requirements, this protection may be pneumatic concrete, asphalt spray, or plastic
membrane In the case of a foundation area, the contractor is required to underexcavate
leaving a cover for protection, as required, until immediately prior to placement of the structure
foundation. Any frost-susceptible materials encountered during excavation should be
protected if the excavation is to be left open during an extended period of freezing weather.
8-4.1.2.6 Excavation Record. As the excavation progresses, the project engineer should
keep a daily record of the type of material excavated and the progress made.
8-4.2 Foundation Preparation
8-4.2.1 Good Construction Practices, and Problems. As mentioned previously, the
problems associated with foundation preparation are greatly reduced by following such proper
excavation procedures as maintaining a dry excavation and planning ahead. The principles of
good foundation preparation are simple, but enforcing the provisions of the specifications
concerning the work is more difficult. Inspection personnel must recognize the importance of
this phase of the work since, if not properly controlled, problems can result.
8-4.2.1.1 Stable Foundations. It is most important that a stable foundation be provided.
Thus it may be necessary, particularly in the case of sensitive fine-grained materials, to require
that the final excavation for footings be carefully done with hand tools and that no equipment
be allowed to operate on the final cut surface. To provide a working platform on which to begin
backfill placement on these sensitive materials, it may be necessary to place an initial layer of
granular material.
8-4.2.1.2 Foundations Supported on Rock. If the foundation is to be supported on rock,
the soundness of the exposed rock should be checked by a slaking test (soaking a piece of the
rock in water to determine the resulting degree of deterioration (see paragraph 8-3.2.2), and
visual observation to determine if the rock is in a solid and unshattered condition. If removal of
rock below the foundation level is required, the space should be filled with concrete. A
qualified geological or soils engineer should inspect the area if it is suspected that the material
will deteriorate or swell when exposed to the weather. If necessary, the materials must be
protected from exposure using the methods previously discussed in paragraph 8-4.1.2.
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• Before placement of any structure foundation is begun, the plans should be
rechecked to ensure that all required utilities and conduits under or adjacent to
the foundation have been placed, so that excavating under or undermining the
foundation to place utilities and conduits will not become necessary later.
• Occasionally, it may be found upon completion of the excavation that if a
structure were placed as shown on the plans, it would be supported on two
materials with drastically different consolidation characteristics, such as rock and
soil, rock and backfill, or undisturbed soil and backfill. This situation could occur
because the pre-design subsurface information was inadequate, because the
structure was relocated or reoriented by a subsequent change in the plans,
because of an oversight of the design engineer, or because of the excavation
procedures followed by the contractor. Regardless of the reason, measures
such as over-excavation and placement of subsequent backfill should be taken,
where possible, and in coordination with the design office to provide a foundation
of uniform material. Otherwise, the design office should evaluate the differences
in foundation conditions for possible changes to the structural foundation
elements.
• Preparing the area to receive the backfill consists of cleaning, leveling, and
compacting the bottom of the excavation if the foundation is in soil. All debris
and foreign material, such as trash, broken concrete and rock, boulders, and
forming lumber, should be removed from the excavation. All holes, depressions,
and trenches should be filled with the same material as that specified to be
placed immediately above such a depression, unless otherwise designated, and
compacted to the density specified for the particular material used. If the
depression is large enough to accommodate heavy compacting equipment, the
sides of the depression should have a positive slope and be flat enough for
proper operation of compaction equipment. After the area is brought to a
generally level condition by compacting in lifts in accordance with specifications,
the entire area to receive backfill should be sacrificed to the depth specified, the
water content adjusted if necessary, and the area compacted as specified. If the
foundation is in rock, the area should be leveled as much as possible and all
loose material removed.
• All work in the excavation should be accomplished in the dry; therefore, the
dewatering system should be operated for the duration of this work. Under no
circumstances should the contractor be allowed to dry an area by dumping a
thick layer of dry material over it to blot the excess water. If soil exists at the
foundation level and becomes saturated, it cannot be compacted. The saturated
soil will have to be removed and replaced or drained sufficiently so that it can be
compacted. Any frozen material in the foundation should be removed before
placement of concrete footings or compacted backfill.
8-5 BACKFILL OPERATIONS
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8-5.1 Placement of Backfill. Backfill construction is the refilling of previously
excavated space with properly compacted material. The areas may be quite large, in which
case the backfilling operation will be similar to embankment construction. On the other hand,
the areas may be quite limited, such as confined areas around or between and beneath
concrete or steel structures and areas in trenches excavated for utility lines. Prior to
construction of the backfill, the inspection personnel should become thoroughly familiar with
the various classes of backfill to be used. They should be able to readily identify the materials
on sight, know where the various types of material should be placed, and be familiar with the
compaction characteristics of the soil types.
8-5.2 Good Construction Practices, and Problems. Problems with placement of
backfill will vary from one construction project to another. The magnitude of the problems will
depend on the type of materials available such as backfill, density requirements, and the
configuration of the areas in which compaction is to be accomplished. Problems should be
expected during the initial stages of backfill compaction unless the contractor is familiar with
compaction characteristics of backfill materials. The inspector can be of great assistance to
the contractor during this period by performing frequent water content and density checks.
The information from these checks will show the contractor the effects of the compaction
procedures being used and point out any changes that should be made.
8-5.2.1 Backfilling Procedures. Problems associated with the compaction of backfill
can be minimized by following good backfilling procedures. Good backfilling procedures
include: processing the material (paragraph 8-3.4) before it is placed in the excavation; placing
the material in a uniformly spread loose lift of the proper thickness suited to the compaction
equipment and the type of material to be used; applying the necessary compaction effort to
obtain the required densities; and ensuring that these operations are not performed during
adverse weather. Proper bond should be provided between each lift and also between the
backfill and the sides of the excavation.
8-5.2.2 Compaction Equipment, Backfill Material, and Zones. The type of
compaction equipment used to achieve the required densities will usually depend upon the
type of backfill material being compacted and the type of zone in which the material is placed.
• In open zones, coarse-grained soils that exhibit slight plasticity (clayey sands,
silty sands, clayey gravels, and silty gravels) should be compacted with either
sheepsfoot or rubber-tired rollers; close control of water content is required
where silt is present in substantial amounts. For sands and gravelly sands with
little or no fines, good compaction results are obtained with tractor compaction.
Good compaction can also be achieved in gravels and gravel-sand mixtures with
either a crawler tractor or rubber-tired and steel-wheeled rollers. The addition of
vibration to any of the means of compaction mentioned above will usually
improve the compaction of soils in this category. In confined zones, adequate
compaction of coliesionless soils in either the air-dried or saturated condition can
be achieved by vibratory-plate compactors with a static weight of at least 100
pounds. If the material is compacted in the saturated condition, good compaction
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can be achieved by internal vibration (for example, by using concrete vibrators).
Downward drainage is required to maintain seepage forces in a downward
direction if the placed material is saturated to aid in compaction.
• Inorganic clays, inorganic silts, and very fine sands of low to medium plasticity
are fairly easily compacted in open zones with sheepsfoot or rubber-tired rollers
in the 67 kN (15,000 pound) and above wheel-load class. Some inorganic clays
can be adequately compacted in confined zones using rammer or impact
compactors with a static weight of at least 0.445 kN (100 pounds) provided close
control of lift thickness and water content is maintained.
• Fine-grained, highly plastic materials, though not good backfill materials, can
best be compacted in open zones with sheepsfoot rollers. Sheepsfoot rollers
leave the surface of the backfill in a rough condition, which provides an excellent
bond between lifts. In confined areas the best results, which are not considered
good, are obtained with rammer or impact compactors.
8-5.2.3 Lift Thickness. The loose-lift thickness will depend on the type of backfill
material and the compaction equipment to be used.
• As a general rule, a loose-lift thickness that will result in a 0.15 m (6 in) lift when
compacted can be allowed for most sheepsfoot and pneumatic-tired rollers.
Cohesive soils placed in approximately 0.25 m (10 in) loose lifts will compact to
approximately 0.15 m (6 in), and cohesionless soils placed in approximately 0.20
m (8 in) base lifts will compact to 0.15 m (6 in). Adequate compaction can be
achieved in cohesionless materials of about 0.300 to 0.381 m (12 to 15 in) loose-
lift thickness if heavy vibratory equipment is used. The addition of vibration to
rolling equipment used for compacting cohesive soils generally has little effect on
the lift thickness that can be compacted, although compaction to the desired
density can sometimes be obtained by fewer coverages of the equipment.
• In confined zones where clean cohesionless backfill material is used, a loose-lift
thickness of 0.100 to 0.150 m (4 to 6 in) and a vibratory plate or walk-behind,
dual-drum vibratory roller for compaction is recommended. Where cohesive soils
are used as backfill in confined zones, use of rammer compactors and a loose-lift
thickness of not more than 100 mm (4 in) should be specified. Experience has
shown that "two-by-four" wood rammers, or single air tampers (commonly
referred to as powder puffs" or "pogo sticks") do not produce sufficient
compaction.
8-5.2.4 Density Requirements. In open areas of backfill where structures will not be
constructed, compaction can be less than that required in more critical zones. Compaction to
90 percent of ASTM D 1557 maximum dry density should be adequate in these areas. If
structures are to be constructed on or within the backfill, compaction of cohesionless soils to
within 95 to 100 percent of ASTM D 1557 maximum dry density and of cohesive soils to at
least 95 percent of ASTM D 1557 should be required for the full depth of backfill beneath these
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structures. The specified degree of compaction should be commensurate with the tolerable
amount of settlement, and the compaction equipment used should be commensurate with the
allowable lateral pressure on the structure. Drainage blankets and filters having special
gradation requirements should be compacted to within 95 to 100 percent of ASTM D 1557
maximum dry density. Table 8-5.1 gives a summary of type of compaction equipment,
coverage, and lift thickness for the specified degree of compaction of various soil types.
8-5.2.5 Cold Weather. In areas where freezing temperatures either hamper or halt
construction during the winter, certain precautions can, and should, be taken to prevent
damage from frost penetration and subsequent thaw. Some of these precautions are
presented below.
• Placement of permanent backfill should be deferred until favorable weather
conditions prevail. However, if placement is an absolute necessity during
freezing temperatures, either dry, cohesionless, non frost-susceptible materials
or material containing additives, such as calcium chloride, to lower the freezing
temperature of the soil water should be used. Each lift should be checked for
frozen material after compaction and before construction of the next lift is begun.
If frozen material is found, it should be removed; it should not be disked in place.
Additives should not be used indiscriminately since they will ordinarily change
compaction and water content requirements. Prior laboratory investigation
should be conducted to determine additive requirements and the effect on the
compaction characteristics of the backfill material.
• Under no circumstances should frozen material, from stockpile or borrow pit, be
placed in backfill that is to be compacted to a specified density.
• Prior to halting construction during the winter, the peripheral surface drainage
system should be checked and reworked where necessary to provide positive
drainage of surface water away from the excavation.
• Foundations beneath structures and backfill around structures should not be
allowed to freeze, because structural damage will invariably develop. Structures
should be enclosed as much as possible and heated if necessary. Construction
should be scheduled so as to minimize the amount of reinforcing steel protruding
from a partially completed structure since steel will conduct freezing
temperatures into the foundation.
• Permanent backfill should be protected from freezing. Records should be made
of all temporary coverings that must be removed before backfilling operations are
resumed. A checklist should be maintained to ensure that all temporary
coverings are removed at the beginning of the next construction season.
• During freezing weather, records should be kept of the elevation of all critical
structures to which there is the remotest possibility of damage or movement due
to frost heave and subsequent thaw. It is important that frost-free benchmarks
be established to which movement of any structure can be referenced.
Benchmarks also should be established on the structures at strategic locations
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8-71
prior to freezing weather.
• At the beginning of the following construction season and after the temporary
insulating coverings are removed, the backfill should be checked for frozen
material and ice lenses, and the density of the compacted material should be
checked carefully before backfilling operations are resumed. If any backfill has
lost its specified density because of freezing, it should be removed.
8-5.2.6 Zones Having Particular Gradation Requirements. Zones that have particular
gradation requirements include those needed to conduct and control seepage, such as
drainage blankets, filters, and zones susceptible to frost penetration. Drainage zones are often
extremely important to the satisfactory construction and subsequent performance of the
structure. To maintain the proper functioning of these zones, care must be taken to ensure
that the material placed has the correct gradation and is compacted according to
specifications.

Table 8-5.1 Summary of Compaction Criteriaa
Fill and Backfill
Soil
Group
Soil
Types
Degree of Compaction Equipment No. of Passes
or Coverages
Comp. Lift
Thickness mm
(in)
Placement
Water Content
Field Control
Compacted
90 – 95% of CE
55 maximum
density
75 – 85% of
relative density
Vibratory Rollers
Rubber Tired Rollerb
Crawler Type
Tractorc
Power Hand
Tamperd
Indefinite
2-5 Coverages
2-5 Coverages
Indefinite
Indefinite
300 (12)
200 (8)
150 (6)
Saturate by
Flooding
Control tests at
intervals to
determine
degree of
compaction or
relative density
Pervious(FreeDraining
GW
GP
SW
SP
Semi-Compacted
85 to 90% of CE
55 maximum
density
65 to 75% of
relative density
Rubber Tired Rollerb
Crawler Type
Tractorc
Power Hand
Tamperd
Controlled routing of
construction
equipment
2-5 Coverages
1-2 Coverages
Indefinite
Indefinite
360 (14)
250 (10)
200 (8)
200–250 (8-10)
Saturate by
Flooding
Control tests at
intervals to
determine
degree of
compaction or
relative density,
if needed
Note: The above requirements will be adequate in most construction venues. In special cases where tolerable settlements are unusually small, it may be necessary to
employ additional compaction equivalents to 95-100% of compaction effort. A coverage consists of one application of the wheel of a rubber tired roller or the treads of a
crawler type tractor over each point in the area being compacted. For a sheepsfoot roller , one pass consists of one movement of a sheepsfoot roller drum over the area
being compacted.
a) From TM 5-818-1
b) Rubber – tired rollers having a wheel load between 80 and 111 kN (18,000 and 25,000 lb) with a tire pressure between 552-689 kPa (80-100 psi).
c) Crawler type tractors weighing not < 89 kN (20,000 lbs) / exerting a foot pressure not < 4.5 kPa (6.5psi).
d) Power hand tampers weighing more than 0.44 kN (100 lbs) / pneumatic or gasoline powered.
e) Sheepsfoot roller with a foot pressure between 1724-3448 kPa (250-500 psi)/ tamping feet 180-250 mm (7-10 in) long/ face area between 4500-10300 mm2
(7-16 sq. in. )

Note: The above requirements will be adequate in most construction venues. In special cases where tolerable settlements are unusually small, it may be necessary to
employ additional compaction equivalents to 95-100% of compaction effort. A coverage consists of one application of the wheel of a rubber tired roller or the treads of a
crawler type tractor over each point in the area being compacted. For a sheepsfoot roller , one pass consists of one movement of a sheepsfoot roller drum over the area
being compacted.
Fill and Backfill
Soil
Group
Soil
Types
Degree of Compaction Equipment No. of Passes
or Coverages
Comp. Lift
Thickness
mm (in)
Placement Water Content Field
Control
Compacted
90 to 95% of
CE55
maximum
density
Rubber tired Rollerb
Sheepsfoot Roller e
Power hand Tamperd
2-5 Coverages
4-8 Passes
Indefinite
200 (8)
150 (6)
100 (4)
Optimum water content Control
tests at
intervals to
determine
degrees of
compaction
Semi-PerviousandImpervious
CM
CC
SM
SC
ML
CL
OL
OH
MH
CH
Semi-Compacted
85 to 90% of
CE55
maximum
density
Rubber tired rollersb
Sheepsfoot Rollere
Crawler-type Tractorc
Power hand tamperd
Controlled routing of
construction
equipment`
2-4 coverages
4-8 passes
3 coverages
Indefinite
Indefinite
250 (10)
200 (8)
150 (6)
150 (6)
150-200
(6-8)
(A) Optimum water
content
(B) Observation: wet side
maximum water content at
which material can
satisfactorily operate; dry
side minimum water
content required to bond
particles; must not result
in voids or honey-combed
materials.
(A) Control
tests as
shown
(B) Field
control via
visual
inspection
of process
Table 8-5.1 Summary of Compaction Criteriaa
e) Sheepsfoot roller with a foot pressure between 1724-3448 kPa (250-500 psi)/ tamping feet 180-250 mm (7-10 in) long/ face area between 4500-10300 mm
2
(7-16 sq. in. )
f) Rubber – tired rollers having a wheel load between 80 and 111 kN (18,000 and 25,000 lb) with a tire pressure between 552-689 kPa (80-100 psi).
g) Crawler type tractors weighing not < 89 kN (20,000 lbs) / exerting a foot pressure not < 4.5 kPa (6.5psi).
h) Power hand tampers weighing more than 0.44 kN (100 lbs) / pneumatic or gasoline powered.
e) From TM 5-818-1

UFC 3-220-01N
15 AUGUST 2005
8-5.3 Special Problems. In open zones, compaction of backfill will not
generally present any particular problems if proper compaction procedures normally
associated with the compaction of soils are exercised and the materials available for
use, such as backfill, are not unusually difficult to compact. The majority of the
problems associated with backfill will occur in confined zones where only small
compaction equipment producing a low compaction effort can be used or where
because of the confined nature of the backfill zone even small compaction equipment
cannot be operated effectively.
Considerable latitude exists in the various types of small compaction
equipment available. Unfortunately, very little reliable information is available on the
capabilities of the various pieces of equipment. Depending upon the soil type and
working room, it may be necessary to establish lift thickness and compaction effort
based essentially on trial and error in the field. For this reason, close control must be
maintained particularly during the initial stages of the backfill until adequate compaction
procedures are established.
8-5.3.1 Difficult Structures. Circular, elliptical and arched walled structures are
particularly difficult to adequately compact backfill beneath the under side of haunches
because of limited working space. Generally, the smaller the structure the more difficult
it is to achieve required densities. Rock, where encountered, must be removed to a
depth of at least 0.15 m (6 in) below the bottom of the structure and the overdepth
backfilled with suitable material before foundation bedding for the structure is placed.
Some alternate bedding and backfill placement methods are discussed below.
• One method is to bring the backfill to the planned elevation of the spring
line using conventional heavy compaction equipment and methods. A
template in the shape of the structure to be bedded is then used to
reexcavate to conform to the bottom contours of the structure. If the
structure is made of corrugated metal, allowance should be made in the
grade for penetration of the corrugation crests into the backfill upon
application of load. Success of this method of bedding is highly
dependent on rigid control of grade during reexcavation using the
template. This procedure is probably the most applicable where it is
necessary to use a cohesive backfill.
• Another method of bedding placement is to sluice a clean granular backfill
material into the bed after the structure is in place. This method is
particularly adapted to areas containing a maze of pipes or conduits.
Adequate downward drainage, generally essential to the success of this
method, can be provided by sump pumps or, if necessary, by pumping
from well points. Sluicing should be accompanied by vibrating to ensure
adequate soil density. Concrete vibrators have been used successfully for
this purpose. This method should be restricted to areas where conduits or
pipes have been placed by trenching or in an excavation that provides
confining sides. Also, this method should not be used below the
groundwater table in seismic zones, since achieving densities high
enough to assure stability in a seismic zone is difficult.
8-74

UFC 3-220-01N
15 AUGUST 2005
distress include: settlement or swelling of the backfill around the structure; sudden or
gradual change of instrumentation data; development of cracks in structural walls; and
adverse seepage problems. Detailed construction records are important for defining
potential distress areas and assessing the mechanisms causing the distress.
8-6 SPECIFICATION PROVISIONS
8-6.1 General. The plans and specifications define the project in detail and
show how it is to be constructed. They are the basis of the contractor's estimate and of
the construction contract itself. The drawings show the physical characteristics of the
structure, and the specifications cover the quality of materials, workmanship, and
technical requirements. Together they form the guide and standard of performance that
will be required in the construction of the project. Once the contract is let, the plans and
specifications are binding on both the Contracting Officer and the contractor and are
changed only by written agreement. For this reason, it is essential that the contractor
and the Contracting Officer's representative anticipate and resolve differences that may
arise in interpreting the intent and requirements of the specifications. The ease with
which this can be accomplished will depend on the clarity of the specifications and the
background and experience of the individuals concerned. Understanding of
requirements and working coordination can be improved if unusual requirements are
brought to the attention of prospective bidders and meetings for discussion are held
prior to construction. Situations will undoubtedly arise that are not covered by the
specifications, or conditions may occur that are different from those anticipated. Close
cooperation is required between the contractor and the inspection personnel in
resolving situations of this nature; if necessary, to be fair to both parties a change order
should be issued.
8-6.2 Preparation of Contract Specifications. Preparation of contract
specifications is easier if an outline of general requirements is available to the
specification writer. However, it would be virtually impossible to prepare a guide
specification that anticipates all problems that may occur on all projects. Therefore,
contract specifications must be written to satisfy the specific requirement of each
project. Some alternate specification requirements that might be considered for some
projects are discussed below.
8-6.2.1 Excavation. The section of the specifications dealing with excavation
contains information on drainage, shoring and bracing, removal and stockpiling, and
other items, and refers to the plans for grade requirements and slope lines to be
followed in excavating overburden soils and rock.
8-6.2.2 Drainage. For some projects the specifications will require the contractor
to submit a plan of his excavation operations to the Contracting Officer for review. The
plans and specifications will require that the excavation and subsequent construction
and backfill be carried out in the dry. To meet this requirement, a dewatering system
based on the results of groundwater studies may be included in the plans. Also, for
some projects the specifications may require the contractor to submit his plan for
controlling groundwater conditions. The specifications should likewise indicate the
possibility of groundwater conditions being different from those shown in the subsurface
8-76

UFC 3-220-01N
15 AUGUST 2005
investigation report due to seasonal or unusual variations or insufficient information,
since the contractor will be held responsible for controlling the groundwater flow into the
excavation regardless of the amount. To this end, the specifications should provide for
requiring the contractor to submit a revised dewatering plan for review where the
original dewatering plan is found to be inadequate.
8-6.2.3 Shoring and Bracing. The specifications either will require the contractor
to submit for review his plans for the shoring and bracing required for excavation or will
specify shoring and bracing required by subsurface and groundwater conditions and
details of the lines and grades of the excavation. In the latter case, the contractor may
be given the option to submit alternate plans for shoring and bracing for review by the
Contracting Officer. The plans will present the necessary information for the design of
such a system if the contractor is allowed this option.
8-6.2.4 Stockpiling. Provisions for stockpiling materials from required excavation
according to type of backfill may or may not be included in the specifications.
Generally, procedures for stockpiling are left to the discretion of the contractor, and a
thorough study should be made to substantiate the need for stockpiling before such
procedures are specified. There are several conditions under which inclusion of
stockpiling procedures in the specifications would be desirable and justified. Two such
conditions are discussed in the following paragraphs.
• Under certain conditions, such as those that existed in the early stages of
missile base construction where time was an important factor, it may be
necessary or desirable to award contracts for the work in phases. As a
result, one contractor may do the excavating and another place the
backfill. It is probable that the excavation contractor will have little or no
interest in stockpiling the excavated materials in a manner conducive to
good backfilling procedures. When such a situation can be foreseen, the
specifications should set forth stockpiling procedures. The justification for
such requirements would be economy and optimum use of materials
available from required excavation as backfill.
• The specifications will contain provisions for removing, segregating, and
stockpiling or disposing of material from the excavation and will refer to
the plans for locations of the stockpiles. The subsoil conditions and
engineering characteristics requirements may state that the specifications
must be quite definite concerning segregation and stockpiling procedures
so that the excavated materials can be used most advantageously in the
backfill. The specification may require that water be added to the material
or the material be aerated as it is stockpiled to approximate optimum
water content, that the stockpile be shaped to drain and be sealed from
accumulation of excess water, and that the end dumping of material on
the stockpile be prohibited to prevent segregation of material size or type
along the length of the stockpile.
An alternative to this latter action would be to specify the various classes
of backfill required and leave the procedure for stockpiling the materials by type to the
discretion of the contractor. In this case, the contractor should be required to submit a
8-77

UFC 3-220-01N
15 AUGUST 2005
detailed plan for excavating and stockpiling the material. The plan should indicate the
location of stockpiles for various classes of backfill so that the material can be tested for
compliance with the specifications. The contractor may elect to obtain backfill material
from borrow or commercial sources rather than to separate and process excavated
materials. Then the specifications should require that stockpiles of the various classes
of needed backfill be established at the construction site in sufficient quantity and far
enough in advance of their use to allow for the necessary testing for approval unless
conditions are such that approval of the supplier's stockpile or borrow source can be
given.
8-6.3 Foundation Preparation. The provisions for preparation for structures
will generally not be grouped together in the specifications but will appear throughout
the earthwork section of the specifications under paragraphs on excavation, protection
of foundation materials, backfill construction, and concrete placement. When a structure
is to be founded on rock, the specifications will require that the rock be firm, unshattered
by blasting operations, and not deteriorated from exposure to the weather. The
contractor will be required to remove shattered or weathered rock and to fill the space
with concrete.
8-6.3.1 Structures on Soil. Specifications for structures founded on soil require
the removal of all loose material and all unsuitable material, such as organic clay or silt,
below the foundation grade. When doubt exists as to the suitability of the foundation
materials, a soils engineer should inspect the area and his recommendations should be
followed. When removal of rock material below the planned foundation level is required,
the over-excavation will usually require filling with concrete. The specifications also
require dewatering to the extent that no backfill or structural foundation is placed in the
wet.
Specifications for preparation of the soil foundation to receive backfill
require removing all debris and foreign matter, making the area generally level, and
scarifying, moistening, and compacting the foundation to a specified depth, generally
305 mm (12 in). Specific provisions may or may not be given with respect to leveling
procedures.
8-6.4 Backfill Operations. The specifications define the type or types of
material to be used for backfill construction and provide specific instructions as to where
these materials will be used in the backfill. The percentage of ASTM D 1557 maximum
dry density to be obtained, determined-by a designated standard laboratory compaction
procedure, will be specified for the various zones of backfill. The maximum loose-lift
thickness for placement will also be specified. Because of the shape of the compaction
curve, the degree of compaction specified can be achieved only within a certain range
of water contents for a particular compaction effort. Though not generally specified in
military construction, the range of water contents is an important factor affecting
compaction.
8-6.4.1 Compacting. The specifications sometimes stipulate the characteristics
and general type of compaction equipment to be used for each of the various types of
backfill. Sheepsfoot or rubber-tired rollers, rammer or impact compactors, or other
suitable equipment are specified for fine-grained, plastic materials. Non-cohesive, free
8-78

UFC 3-220-01N
15 AUGUST 2005
draining materials are compacted by saturating the material and operating crawler-type
tractor, surface or internal vibrators, vibratory compactors, or other similar suitable
equipment. The specifications generally will prohibit the use of rock or rock-soil
mixtures as backfill in this type of construction. However, when the use of backfill
containing rock is permitted, the maximum size of the rock is given in the specifications
along with maximum lift thickness, loading, hauling, dumping, and spreading
procedures, type of compaction equipment, and method of equipment operation. The
specifications should prohibit the use of rock or rock-soil mixtures as backfill in areas
where heavy equipment cannot operate. Rock / soil mixtures having greater than 8 to
10 percent binder should be prohibited in all areas. In the case of backfill containing
rock, the density is not generally specified. Obtaining adequate density is usually
achieved by specifying the compaction procedures. The specifications may require that
these procedures be developed in field test sections.
Specifications may also require specific equipment and procedures to ensure adequate
bedding for round-bottom structures such as tunnels, culverts, conduits, and tanks.
Procedures normally specified for placement of bedding for these types of structure are
discussed in paragraph1.3.
8-6.4.2 Backfill Against Structures. The specifications will state when backfill
may be placed against permanent concrete construction with respect to the time after
completion; this time period is usually from 7 to 14 days. To provide adequate
protection of the structures during backfill construction, the specifications require that
the backfill be built up symmetrically on all sides and that the area of operation of heavy
equipment adjacent to a structure be limited. Also, the minimum thickness of
compacted materials to be placed over the structures by small compaction equipment,
such as vibratory plate or rammer type, will be specified before heavy equipment is
allowed to operate over the structure. The specifications require that the surface of the
backfill be sloped to drain at all times when necessary to prevent ponding of water on
the fill. The specifications also provide for groundwater control, so that all compacted
backfill will be constructed in the dry. Where select, freedraining, cohesionless soils of
high permeability are required in areas where compaction is critical, the specifications
list gradation requirements. Gradation requirements are also specified for materials
used for drains and filters.
Unusually severe specification requirements may be necessary for backfill
operations in confined areas. The requirements may include strict backfill material type
limitation, placement procedures, and compaction equipment.
8-6.4.3 Protection from Freezing. It is not the policy of the Government to
inform the contractor of ways to accomplish the necessary protection from freezing
temperatures. However, to ensure that adequate protection is provided, it may be
necessary to specify that the contractor submit detailed plans for approval for such
protection.
8-7 STABILIZATION OF SUBGRADE SOILS
8-79

UFC 3-220-01N
15 AUGUST 2005
8-7.1 General . The applicability and essential features of foundation soil
treatments are summarized in Tables 8-7.1 and 8-7.2 and in Figure 8-7.1. The depth of
stabilization generally must be sufficient to absorb most of the foundation pressure bulb.
The relative benefits of vibrocompaction, vibrodisplacement compaction, and
precompression increase as load intensity decreases and size of loaded area
increases, soft, cohesive soils treated in place are generally suitable only for
low-intensity loadings. Soil stabilization of wet, soft soils may be accomplished by
addition of lime; grout to control water flow into excavations to reduce lateral support
requirements or to reduce liquefaction or settlement caused by adjacent pile driving;
seepage control by electro osmosis; and temporary stabilization by freezing. The range
of soil grain sizes for which each stabilization method is most applicable is shown in
figure 8-7.1.
8-7.2 Vibrocompaction. Vibrocompaction methods (blasting, terraprobe, and
vibratory rollers) can be used for rapid densification of saturated cohesionless soils
(Figure 8-7.1.) The ranges of grain-size distributions suitable for treatment by
vibrocompaction, as well as vibroflotation, are shown in Figure 8-7.2. The effectiveness
of these methods is greatly reduced if the percent finer than the 0.075 Micron (No. 200)
sieve exceeds about 20 percent or if more than about 5 percent is finer than 0.002
millimeter, primarily because the hydraulic conductivity of such materials is too low to
prevent rapid drainage following liquefaction. The usefulness of these methods in partly
saturated sands is limited, because the lack of an increase of pore water pressure
impedes liquefaction. Lack of complete saturation is less of a restriction to use of
blasting because the high-intensity shock wave accompanying detonation displaces
soil, leaving depressions that later can be backfilled.
8-7.2.1 Blasting. Theoretical design procedures for densification by blasting are
not available and continuous onsite supervision by experienced engineers having
authority to modify procedures as required is essential if this treatment method is used.
A surface heave of about 150 mm (6 in) will be observed for proper charge sizes and
placement depths. Surface cratering should be avoided. Charge sizes of less than 1.8
to more than 27 kg (4 to more than 60 lb) have been used. The effective radius of
influence for charges using (meters = lb) 60 percent dynamite is as follows:
R = 3M1/3
(feet)
8-7.2.1.1 Charge Spacings. Charge spacings of 3 to 7.62 m (10 to 25 ft) are
typical. The center of charges should be located at a depth of about two thirds the
thickness of the layer to be densified, and three to five successive detonations of
several spaced charges each are likely to be more effective than a single large blast.
Little densification is likely to result above about a 1 m (3 ft) depth, and loosened
material may remain around blast points. Firing patterns should be established to avoid
the "boxing in" of pore water. Free-water escape on at least two sides is desirable.
8-7.2.1.2 Pre-Flooding. If blasting is used in partly saturated sands or loess, pre-
flooding of the site is desirable. In one technique, blast holes about 76 to 88 mm (3 to 3
½ in) in diameter are drilled to the desired depth of treatment, then small charges
8-80

UFC 3-220-01N
15 AUGUST 2005
8-83
settlements to 25.4 mm (1 in) and vibroflot spacing. Allowable pressures for "essentially
cohesionless fills" are less than for clean sand deposits, because such fills invariably
contain some fines and are harder to densify.
Continuous square or triangular patterns are often used over a building
site. Alternatively, it may be desired to improve the soil only at the locations of
individual spread footings. Patterns and spacings required for an allowable pressure of
287 kPa (3 tons per sq ft) and square footings are given in Table 8-7.3.

Suitable
Soil
Condition/
Type
Maximum
Effective
Treatment
Depth
meters (ft)
Economical
Size of
Treated
Area
Special
Materials
Required
Special
Equipment
Required
Properties
of Treated
Material
Special
Advantages
and
Limitations
Relative
Costs
(1976)
Blasting Shock waves
and
vibrations
causes
liquefaction,
displacement
Saturated,
clean
sands,
partially
saturated
sands and
silts after
flooding`
18 M
(60 ft)
Small areas
can be
treated
economically
Explosives;
backfill to
plug drill
holes
Jetting or
drilling
machinery
Can obtain
relative
densities
to 70-80%;
may get
variable
density
Rapid,
inexpensive;
can treat
small areas,
variable
properties;
no
improvement
near surface
dangerous
Low $0.50
to $1.00 per
cubic meter
(cubic yard)
Terraprobe Densification
by vibrations,
liquefaction
induced
settlement
under
overburden
Saturated
or clean
dry sand
18 M
(60 ft)
(ineffective
3.6 M (12
ft) depth
and
above)
1000M
2
>1200yd2
None Vibratory
pile driver
and 75mm
diameter
open steel
pipe
Can obtain
relative
densities
of 80% or
more
Rapid,
simple; good
underwater
and w/ soft
underlayers;
difficult to
penetrate
stiff upper
layers; not
good in
poorly
saturated
soils.
Moderate;
$1.50-
.$3.25/cubic
meter
(cubic yd)
$2.00 cubic
meter
(cubic yd)
average
Vibro-Compaction
Vibratory
Rollers
Densification
by vibration,
liquefaction
induced
settlement
under roller
weight
Cohesion-
less soils
1.8-3 M
(6-10 ft)
Any size None Vibratory
roller
Can obtain
very high
relative
densities
Best method
for thin
layers and
lifts
Low

Suitable Soil
Condition/
Type
Maximum
Effective
Treatment
Depth
(feet)
Economical
Size of
Treated
Area
Special
Materials
Required
Special
Equipment
Required
Properties
of Treated
Material
Special
Advantages
and
Limitations
Relative
Costs
(1976)
Compaction
piles
Densification
by
displacement
of pile
volume and
vibration
during
drilling
Loose sandy
soils, partly
saturated
clay like
soils; loess
1.8 M
(60ft)
Small to
moderate
Pile
material
(often
sand or
soil +
cement
Pile driver Can obtain
high
densities;
good
uniformity
Useful in soils
w/ fines,
uniform
compactioneasy
to check results,
slow, limited
improvement in
upper 300 –
600 mm (1-2 ft)
High
Heavy
Tamping
(Dynamic
consolidation)
Repeated
application of
high intensity
impacts @
surface.
Cohesionless
best; other
types can
also be
improved
15- 18 M
(50-60 ft)
>3344 M
2
(4000 yd2
)
None Tamper of
10-40 tons;
high
capacity
crane
Can obtain
high
relative
densities;
reasonable
uniformity
Simple, rapid;
suitable for
some soils w/
fines; usable
above and
below water;
requires control;
must be away
from existing
structures.
Less than
vibro-
floatation.
Vibro-DisplacementCompaction
Vibrofloatation Densification
by vibration
and
compaction
of backfill
material
Cohesionless
soils with
less than
20%
90ft >1000 M2
(1200 yd2
)
Granular
backfill
Vibroflot;
crane
Can obtain
high
relative
densities;
good
uniformity
Useful in
saturated and
partially
saturated soils;
uniformity
$10.00-
$25.00/m
2
(
yd2
);
$1.00/m2
(
yd2
); may
cost about
half of
compaction
or concrete
piles.

Suitable
Soil
Condition/
Type
Maximum
Effective
Treatment
Depth
(feet)
Economical
Size of
Treated
Area
Special
Materials
Required
Special
Equipment
Required
Properties
of Treated
Materials
Special
Advantages
and
Limitations
Relative
Costs
(1976)
Particulate
Grouting
Penetration
grouting; fill
soil pores
w/ cement
and/or clay
Medium to
coarse
sand and
gravel
Unlimited Small Grout,
water
Mirrors,
tanks,
pumps,
hoses
Impervious,
high strength
with cement
grout;
eliminates
liquefacation
danger
Low cost
grouts, high
strength:
limited to
coarse
grained soils
hard to
evaluate
Lowest of
the grout
systems
Chemical
grouting
Solutions
of two or
more
chemicals
react in soil
pores to
form a gel
or a solid
precipitate
Medium
silts and
coarser
Unlimited Small Grout,
water
Mirrors,
tanks,
pumps,
hoses
Impervious,
low to high
strength;
eliminate
liquefaction
danger
Low
viscosity,
controllable
gel time,
good water
shut-off;
high cost,
hard to
evaluate
High to
very high
$30/m
2
-
$80/m2
typical
GroutingandInjection
Pressure
Injected Lime
Lime slurry
injected to
shallow
depths
under high
pressure
Expansive
clays
Unlimited;
but 2-3 m
usual
Small Lime,
water,
surfactant
Slurry
tanks,
agitators,
injectors
Lime
encapsulated
zones
formed by
chemicals
resulting
from cracks,
root holes,
hydraulic
fracture.
Rapid and
economical
treatment for
foundation
soils under
light
structures.
$2.50-
$3.00/m
of ground
surface
area.

Suitable
Soil
Condition/
Type
Maximum
Effective
Treatment
Depth
(feet)
Economical
Size of
Treated
Area
Special
Materials
Required
Special
Equipment
Required
Properties
of Treated
Materials
Special
Advantages
and
Limitations
Relative
Costs
(1976)
GroutingandInjection(Continued)
Displacement
Grout
Highly
viscous
grout acts
as radial
hydraulic
jack when
pumped in
under high
pressure
Soft, fine
grained
soils;
foundation
soils with
large voids
or cavaties
Unlimited,
but a few,
as usual
Small Soil,
cement,
water
Batching
equipment,
high
pressure
pumps and
hoses
Grout bulbs
within
compressed
soil matrix
Good for
correction of
differential
settlements,
filling large
voids;
careful
control
required
Low for
materials;
high for
injection
process.

Suitable
Soil
Condition/
Type
Maximum
Effective
Treatment
Depth
(feet)
Economical
Size of
Treated
Area
Special
Materials
Required
Special
Equipment
Required
Properties of
Treated
Material
Special
Advantages
and
Limitations
Relative
Costs
(1976)
Preloading Load is
applied
sufficiently in
advance of
construction
so that
compression
of soft soils
is completed
prior to site
development
Normally
consolidated
soft clays,
silts, organic
deposits,
completed
sanitary
landfills
------ >1000m
2
Earth fill
or other
material
for loading
the site;
sand or
gravel for
drainage
blanket.
Earth
moving
equipment;
large H2O
tanks or
vacuum
drainage
systems
may be
used;
settlement
markers;
piezometers
Reduced water
content and
void ratio/
increased
strength
Easy, theory
well
developed,
consistent
and uniform;
requires long
time (sand
drains or
wicks can be
used to
reduce
consolidation
time
Low /
moderate
if vertical
drains are
required.
Precompression
Surcharge
fills
Fill in excess
of that
required
permanently
is applied to
achieve a
given amt of
settlement in
a shorter
time; excess
fill then
removed
Normally
consolidated
soft clays,
silts, organic
deposits:
completed
sanitary
landfills
------ >1000m
2
Earth fill /
other
material
for
loading/
sand or
gravel as
drainage
blanket
Earth
moving
equipment;
settlement
markers;
piezometers
Reduced H2O
content, void
ratios and
compressibility:
increased
strength
Faster than
preloading
w/o
surcharge;
theory well
developed;
extra
material
handing; use
sand drains/
wicks
Moderate/
Sand
drains
moderate
cost

Suitable
Soil
Condition/
Type
Maximum
Effective
Treatment
Depth
(feet)
Economical
Size of
Treated
Area
Special
Materials
Required
Special
Equipment
Required
Properties of
Treated
Material
Special
Advantages
and
Limitations
Relative
Costs
(1976)
Dynamic
Consolidation
High energy
impacts
compress
and dissolve
gas in pores
to give
immediate
settlement;
increased
pore
pressure
gives
subsequent
drainage.
Partly
saturated
fine grained
soils;
quarternary
clays clays
w/ 1-4 gas
in micro –
bubbles
30 m >15000-
30000 m
2
>15000-
30000 m2
Tamper of
10-40 tons,
high
capacity
cranes
Reduced water
content, void
ratio and
compressability;
Increased
strength
Faster than
preloading,
economical
on large
areas;
uncertain
mechanism
in clays; less
uniformity
than
preloading
< preload
fills w/
sand
drains
Precompression(Continued)
Electro-
osmosis
DC current
causes H2O
to flow from
anode to
cathode
where it is
then
removed
Normally
consolidated
silts and
silty clays
10-20m Small Anodes
(rebar or
aluminum)
Cathodes
(well
points or
rebar)
D/C power
supply,
wiring,
metering
system
Reduced water
content and
compressibility;
increased
strength,
electrochemical
hardening
No fill
loading
required, can
use in
confined
areas,
relatively
fast, non-
uniform
properties
between
electrodes;
useless in
highly
conductive
soils
High

Suitable
Soil
Condition/
Type
Maximum
Effective
Treatment
Depth
(feet)
Economical
Size of
Treated
Area
Special
Materials
Required
Special
Equipment
Required
Properties of
Treated
Material
Special
Advantages
and
Limitations
Relative
Costs
(1976)
Remove
and
replace,
with /
without
admixtures
Foundation
soil
excavated;
improved
by drying or
admixtures
Inorganic
soils
10 m Small Only if
admixtures
are needed
Excavation
and
compaction
equipment;
dehydrating
system
Increased
strength and
stiffness;
reduced
compressibility
Uniform,
controlled
foundation
soils when
replaced;
may require
large area of
de-watering.
High
Moisture
barriers
Excess
water in
foundation
soils is
prevented
Expansive
soils
5 m Small Membranes,
gravel, lime
or asphalt
Excavating,
trenching,
and
compaction
equipment
Original
natural or as
compacted
properties
retained
Best used
with small
structures/
may not be
100%
effective.
Low to
moderate
Pre-wetting Soil is
brought to
final
estimated
water
content
prior to
construction
Expansive
soils
2-3 m Small Water Water tanks Decreased
swelling
potential
Low cost,
best used for
small light
constructions;
shrinking and
swelling may
sill occur
Low
Miscellaneous
Structural
Fills (with
or without
admixtures)
Fill
distributes
loads to
underlying
soils
Use over
soft clays
or organic
soils,
marsh
lands
------ Small Sand,
gravel,
fly/bottom
ash,
clam/oyster
shell ,
incinerator
ash
Compaction
equipment
Soft subgrade
protected by
structural
load-bearing
fill
High
strength,
good load
distribution to
underlying
soft soils.
Moderate
to high.

Table 8-7.2 Applicability of Foundation Soil Improvement for Different Structures and Soil Types
(for Efficient Use of Shallow Foundations)
Probability of Advantageous Use of Soil Improvement
Techniques
Category of
Structure
Structure Permissible
Settlement
Load Intensity/ Usual
Bearing Pressure
Required kPa (tsf)
Loose
Cohesionless
Soils
Soft Alluvial
Deposits
Old, Inorganic
Soils
High rise/ more than
six stories
Small<25-50mm High 287-96 ( 3-1 ) High Unlikely Low
Medium rise 3-6
stories
Small<25-50mm Moderate 192 (2) High Low Good
Office/Apartment
Frame or load
bearing
construction Low rise
1-3 stories
Small<25-50mm Low 96-192 (1-2 ) High Good High
Large span w/heavy
machines,
cranes;process and
power plants
Small<25-50mm
Differential
Settlement Critical
Variable/ high local
concentrations to >383
(4)
High Unlikely Low
Framed warehouses
& factories
Moderate Low 96-192 (1-2 ) High Good High
Industrial
Covered storage,
storage rack
systems, production
areas
Low to moderate Low <192 (2) High Good High
Water /waste water
treatment plants
Moderate
Differential
settlement important
Low <14364 (150)
<144 (1.5)
High, if needed
at all
High High
Storage tanks Moderate to high,
Diff. maybe critical
High/up to 28728 (300) High, if needed
at all
High High
Open storage Areas High High/up to 28728 (300) High, if needed
at all
High High
Others
Enbankments/
Abutments
Moderate to high High/up to 28728 (300) High, if needed
at all
High High

UFC 3-220-01N
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Figure 8-7.1 Applicable Grain-size Ranges for Different Stabilization Methods
(Courtesy of J. K. Mitchell, “Innovations in Ground Stabilization,”
Chicago Soil Mechanics Lecture Series, Innovations in Foundation
Construction, Illinois Section, 1972. Reprinted by permission of The
American Society of Civil Engineers, NewYork.)
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Figure 8-7.2 Range of Particle-size Distributions Suitable for Densification by
Vibrocompaction
(Courtesy of J. K. Mitchell, “Innovations in Ground Stabilization,”
Chicago Soil Mechanics Lecture Series, Innovations in Foundation
Construction, Illinois Section, 1972. Reprinted by permission of The
American Society of Civil Engineers, NewYork.)
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Figure 8-7.3 Sand Densification Using Vibratory Rollers
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Figure 8-7.4 Relative Density as a Function of Vibrofloat Hole Spacings
8-7.4 Grouting and Injection. Grouting is a high-cost soil stabilization method
that can be used where there is sufficient confinement to permit required injection
pressures. It is usually limited to zones of relatively small volume and to special
problems. Some of the more important applications are control of groundwater during
construction; void filling to prevent excessive settlement; strengthening adjacent
foundation soils to protect against damage during excavation, pile driving, etc.; soil
strengthening to reduce lateral support requirements; stabilization of loose sands
against liquefaction; foundation underpinning; reduction of machine foundation
vibrations; and filling solution voids in calcareous materials,
8-7.4.1 Grout Types and Groutability. Grouts can be classified as particulate or
chemical. Portland cement is the most widely used particulate grouting material.
Grouts composed of cement and clay are also widely used, and lime-slurry injection is
finding increasing application. Because of the silt-size particles in these materials, they
cannot be injected into the pores of soils finer than medium to coarse sand. For
successful grouting of soils, use the following guide
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Type 1 portland cement, Type III portland cement, and processed bentonite cannot be
used to penetrate soils finer than 30, 40, and 60 mesh sieve sizes, respectively.
Different types of grouts may be combined to both coarse- and fine-grained soils.
8-7.4.2 Cement and Soil-Cement Grouting. See the American Society of Civil
Engineers Grouting Publications for cement and soil-cement grouting.
8-7.4.3 Chemical Grouting. To penetrate the voids of finer soils, chemical grout
must be used. The most common classes of chemical grouts in current use are
silicates, resins, lignins, and acrylamides. The viscosity of the chemical-water solution
is the major factor controlling groutability. The particle-size ranges over which each of
these grout types is effective is shown in Figure 8-7.6.
8-7.5 Precompression.
8-7.5.1 Preloading. Earth fill or other material is placed over the site to be
stabilized in amounts sufficient to produce a stress in the soft soil equal to that
anticipated from the final structures. As the time required for consolidation of the soft
soil may be long (months to years) and varies directly as the square of the layer
thickness and inversely as the hydraulic conductivity, preloading alone is likely to be
suitable only for stabilizing thin layers and with a long period of time available prior to
final development of the site.
8-7.5.1.1 Surcharge Fills. If the thickness of the fill placed for pre-loading is
greater than that required to induce stresses corresponding to structure-induced
stresses, the excess fill is termed a surcharge fill. Although the rate of consolidation is
essentially independent of stress increase, the amount of consolidation varies
approximately in proportion to the stress increase. It follows, therefore, that the
preloading fill plus surcharge can cause a given amount of settlement in shorter time
than can the preloading fill alone. Thus, through the use of surcharge fills, the time
required for preloading can be reduced significantly.
The required surcharge and loading period can be determined using
conventional theories of consolidation. Both primary consolidation and most of the
secondary compression settlements can be taken out in advance by surcharge fills.
Secondary compression settlements may be the major part of the total settlement of
highly organic deposits or old sanitary landfill sites.
Because the degree of consolidation and applied stress vary with depth, it
is necessary to determine if excess pore pressures will remain at any depth after
surcharge removal. If so, further primary consolidation settlement under permanent
loadings would occur. To avoid this occurrence, determine the duration of the
surcharge loading required for points most distant from drainage boundaries.
The rate and amount of preload may be controlled by the strength of the
underlying soft soil. Use berms to maintain foundation stability and place fill in stages to
permit the soil to gain strength from consolidation. Predictions of the rates of
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Figure 8-7.5 Allowable bearing pressure on cohesionless soil layers stabilized by
vibroflotation
Table 8-7.3 Vibroflotation Patterns for Isolated Footings for an Allowable Bearing
Pressure
Square Footing
Size in meters
(feet)
Vibroflotation
Points
Center to Center
Spacing in meters
(feet)
Pattern
1.2 (4.0) 1 --- ---
1.4 – 1.7 (4.5 – 5.5) 2 1.8 (6.0) Line
1.8 – 2.1 (6 - 7) 3 2.3 (7.5) Triangle
2.3 – 2.9 (7.5 - 9.5) 4 1.8 (6.0) Square
3.0 – 3.7 (10 – 12) 5 2.3 (7.5) Square +1
@ center
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Figure 8-7.6 Soil Particle Sizes Suitable for Different Grout Types and Several
Concentrations and Viscosities Shown
8-7.6 Reinforcement. The supporting capacity of soft, compressible ground
may be increased and settlement reduced through use of compression reinforcement in
the direction parallel to the applied stress or tensile reinforcement in planes normal to
the direction of applied stress. Commonly used compression reinforcement elements
include mix-in-place piles and walls. Strips and membranes are used for tensile
reinforcement, with the latter sometimes used to form a moisture barrier as well.
8-7.6.1 Mix-in-Place Piles and Walls. Several procedures are available, most of
them patented or proprietary, which enable construction of soil-cement or soil-lime in
situ. A special hollow rod with rotating vanes is augered into the ground to the desired
depth. Simultaneously, the stabilizing admixture is introduced. The result is a pile of up
to 0.6 meters (2 feet) in diameter. Cement, in amounts of 5 to 10 percent of the dry soil
weight, is best for use in sandy soils. Compressive strengths in excess of 9.6 mPa (200
kips) per sq ft can be obtained in these materials. Lime is effective in both expansive
plastic clays and in saturated soft clay. Compressive strengths of about 0.96 – 1.92
kPa (20 to 40 kips) per square foot are to be expected in these materials. If overlapping
piles are formed, a mix-in-place wall results.
8-7.6.2 Vibroreplacement Stone Columns. A vibroflot is used to make a
cylindrical, vertical hole under its own weight by jetting to the desired depth. Then, up to
1 m2
(cubic yard) coarse granular backfill, usually gravel or crushed rock of 19 to 25 mm
(¾ to 1 in) diameter is dumped in, and the vibroflot is used to compact the gravel
vertically and radially into the surrounding soft soil. This process of backfilling and
compaction by vibration is continued until the densified stone column reaches the
surface.
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8-7.6.3 Strips and Membranes. Low-cost, durable waterproof membranes, such
as polyethylene, polypropylene asphalt, and polyester fabric asphalt, have had
application as moisture barriers. At the same time, these materials have sufficient
tensile strength that when used in envelope construction, such as surrounding a
well-compacted, fine-grained soil, the composite structure has a greater resistance to
applied loads than conventional construction with granular materials. The reason is that
any deformation of the enveloped soil layer causes tension in the membrane, which in
turn produces additional confinement on the soil and thus increases its resistance to
further deformation.
In the case of a granular soil where moisture infiltration is not likely to be
detrimental to strength, horizontally bedded thin, flat metal or plastic strips can act as
tensile reinforcing elements. Reinforced earth has been used mainly for earth retaining
structures; however, the feasibility of using reinforce earth slabs to improve the bearing
capacity of granular soil has been demonstrated.
Model tests have shown that the ultimate bearing capacity can be
increased by a factor of 2 to 4 for the same soil unreinforced. For these tests, the
spacing between reinforcing layers was 0.3 times the footing width. Aggregate strip
width was 42 percent of the length of strip footing.
8-7.6.4 Thermal Methods. Thermal methods of foundation soil stabilization,
freezing or heating, are complex and their costs are high.
8-7.6.4.1 Artificial Ground Freezing. Frozen soil is far stronger and less pervious
than unfrozen ground. Hence, artificial ground freezing has had application for
temporary underpinning and excavation stabilization. More recent applications have
been made to back-freezing soil around pile foundations in permafrost and maintenance
of frozen soil under heated buildings on permafrost. Design involves two classes of
problems; namely, the structural properties of the frozen ground to include the strength
and the stress-strain-time behavior, and thermal considerations to include heat flow,
transfer of water to ice, and design of the refrigeration system.
8-7.6.4.2 Heating. Heating fine-grained soils to moderate temperatures, e.g.,
100°C +, can cause drying and accompanying strength increase if subsequent rewetting
is prevented. Heating to higher temperatures can result in significant permanent
property improvements, including decreases in water sensitivity, swelling, and
compressibility; and increases in strength. Burning of liquid or gas fuels in boreholes or
injection of hot air into 15 to 23 mm (6 to 9 in) diameter boreholes can produce 1.22
meters to 2.13 ms (4 to 7 ft) diameter strengthened zones, after continuous treatment
for about 10 days. Dry or partly saturated weak clayey soils and loess are well suited
for this type of treatment, which is presently regarded as experimental.
8-7.7 Miscellaneous Methods.
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8-7.7.1 Remove and Replace. Removal of poor soil and replacement with the
same soil treated by compaction, with or without admixtures, or by a higher quality
material offer an excellent opportunity for producing high-strength, relatively
incompressible, uniform foundation conditions. The cost of removal and replacement of
thick deposits is high because of the need for excavation and materials handling,
processing, and recompaction. Occasionally, an expensive dewatering system also
may be required. Excluding highly organic soils, pests, and sanitary landfills, virtually
any inorganic soil can be processed and treated so as to form and acceptable structural
fill material.
8-7.7.2 Lime Treatment. This treatment of plastic fine-grained soils can produce
high-strength, durable materials. Lime treatment levels of 3 to 8 percent by weight of
dry soil are typical.
8-7.7.3 Portland Cement. With treatment levels of 3 to 10 percent by dry weight,
portland cement is particularly well suited for low-plasticity soils and sand soils.
8-7.7.4 Stabilization Using Fills. At sites underlain by soft, compressible soils
and where filling is required or possible to establish the final ground elevation,
load-bearing structural fills can be used to distribute the stresses from light structures.
Compacted sands and gravels are well suited for this application as are also fly ash,
bottom ash, slag, and various lightweight aggregates, such as expended shale, clam
and oyster shell, and incinerator ash. Admixture stabilizers may be incorporated in
these materials to increase their strength and stiffness.
Clam and oyster shells as a structural fill material over soft marsh deposits
represent a new development. The large deposits of clam and oyster or reef shells that
are available in the Gulf States coastal areas can be mined and transported short
distances economically. Clamshells are 19 to 38 mm (¾, to 1 ½ in) in diameter,
whereas, oyster shells, which are coarser and more elongated, are 50 to 100 mm (2 to
4 in) in size. When dumped over soft ground, the shells interlock; if there are fines and
water present, some cementation develops owing to the high calcium carbonate (>90
percent) content. In the loose state, the shell unit weight is about 3 kPa (63 lbs per sq
ft); after construction, it is about 4.5 kPa (95 lbs per sq ft). Shell embankments "float"
over very soft ground; whereas, conventional fills would sink out of sight. An
approximately 1.5 m (5 ft) thick layer is required to be placed in a single lift. The only
compaction used is from the top of the lift, so the upper several inches are more tightly
knit and denser than the rest of the layer.
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CHAPTER 9
DEWATERING AND GROUNDWATER CONTROL
9-1 INTRODUCTION
engineer to develop methods and details to dewater or control groundwater during
construction of excavations, walls, slopes and foundations. Methods of erosion control
in open excavations, control of groundwater during construction and control of
groundwater in completed structures are presented.
9-1.2 Scope. Apply these Geotechnical criteria to all projects for the military
services. Methods of calculating the amount of ground water runoff, how to control
groundwater by several methods are presented, and the safety aspects can be
determined. The following topics are discussed in the reference.
• Excavations requiring drainage
• Seepage control
• Seepage cutoffs
• Control of surface waters
• Sheet-pile cofferdams
• Foundation underdrainage and waterproofing.
9-1.3 References.
• UFC 3-220-05, Dewatering and Groundwater Control
9-1.4 Secondary.
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CHAPTER 10
FOUNDATIONS IN EXPANSIVE SOILS
10-1 INTRODUCTION
engineer to develop methods and details for repairing existing foundations or design
details for new foundations that are to be constructed in expansive soils.
of design for new construction, soil treatments and construction methods for foundations
in expansive soils are presented in detail in the primary references. Give particular
attention if there is any indication of expansive properties since retro-repairs are
severely expensive. The methods for repair of foundations constructed in expansive
soils are explained in detail. This is a very important aspect of expansive soils since so
many existing small buildings, from homes to small apartment complexes, are effected
by expansive soils; therefore, the retrofit methods of repair that have been used to
substantially repair the structures are extremely important to the designer and are
presented in the primary references. Check every project that is earth related for soils
that have properties that potentially, or are, expansive. More damage to roads and
structures is attributed to not addressing this potentially devastating problem
than any other single soil related problem.
10-1.3 References.
• See Expansive Soils Publications, ASCE in Appendix A
• 2000 International Building Code (IBC 2000) Chapter 18
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CHAPTER 11
FOUNDATIONS IN AREAS OF SIGNIFICANT FROST PENETRATION
11-1 INTRODUCTION
11-1.1 Types of Areas. For purposes of this UFC, areas of significant frost
penetration may be defined as those in which freezing temperatures occur in the ground
to sufficient depth to be a significant factor in foundation design. Detailed requirements
of engineering design in such areas are given in the UFC series, Arctic and Subarctic
Construction (UFC 3-130-01 through 3-130-07.) Areas of significant frost penetration
may be subdivided as follows.
11-1.1.1 Seasonal Frost Areas. Significant ground freezing occurs in these areas
during the winter season, but without development of permafrost. In northern Texas,
significant seasonal frost occurs about 1 year in 10. A little farther north it is
experienced every year. Depth of seasonal freezing increases northward with
decreasing mean annual and winter air temperatures until permafrost is encountered.
With still further decrease of air temperatures, the depth of annual freezing and thawing
becomes progressively thinner.
The layer extending through both seasonal frost and permafrost areas in
which annual freeze-thaw cycles occur is called the annual frost zone. In permafrost
areas, it is also called the active layer. It is usually not more than 3 m (10 ft) thick, but it
may exceed 6 m (20 ft). Under conditions of natural cover in very cold permafrost
areas, it may be as little as 305 mm (1 ft) thick. Its thickness may vary over a wide
range even within a small area. Seasonal changes in soil properties in this layer are
caused principally by the freezing and thawing of water contained in the soil. The water
may be permanently in the annual frost zone or may be drawn into it during the freezing
process and released during thawing. Seasonal changes are also produced by
shrinkage and expansion caused by temperature changes.
11-1.1.2 Permafrost Areas. In these areas, perennially frozen ground is found
below the annual frost zone. In North America, permafrost is found principally north of
latitudes 55 to 65 degrees, although patches of permafrost are found much farther south
on mountains where the temperature conditions are sufficiently low, including some
mountains in the contiguous 48 States. In areas of continuous permafrost, perennially
frozen ground is absent only at a few widely scattered locations, as at the bottoms of
rivers and lakes. In areas of discontinuous permafrost, permafrost is found
intermittently in various degrees. There may be discontinuities in both horizontal and
vertical extent. Sporadic permafrost is permafrost occurring in the form of scattered
permafrost islands. In the coldest parts of the Arctic, the ground may be frozen as deep
as 610 m (2000 ft).
The geographical boundaries between zones of continuous permafrost,
discontinuous permafrost, and seasonal frost without permafrost are poorly defined but
are represented approximately in Figure 11-1
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11-1.2 General Nature Of Design Problems. Generally, the design of
foundations in areas of only seasonal frost follows the same procedure as where frost is
insignificant or absent, except that precautions are taken to avoid winter damage from
frost heave or thrust. In the spring, thaw and settlement of frost-heaved material in the
annual frost zone may occur differentially, and a very wet, poorly drained ground
condition with temporary but substantial loss of shear strength is typical.
11-1.2.1 Permafrost Areas. In permafrost areas, the same annual frost zone
phenomena occur, but the presence of the underlying permafrost introduces additional
potentially complex problems. In permafrost areas, heat flow from buildings is a
fundamental consideration, complicating the design of all but the simplest buildings.
Any change from natural conditions that results in a warming of the ground beneath a
structure can result in progressive lowering of the permafrost table over a period of
years that is known as degradation. If the permafrost contains ice in excess of the
natural void or fissure space of the material when unfrozen, progressive downward thaw
may result in extreme settlements or overlying soil and structures. This condition can
be very serious because such subsidence is almost invariably differential and hence
very damaging to a structure. Degradation may occur not only from building heat but
also from solar heating, as under pavements, from surface water and groundwater flow,
and from underground utility lines. Proper insulation will prevent degradation in some
situations, but where a continuous, source of heat is available, thaw will in most cases
eventually occur.
11-1.2.2 Seasonal Frost Areas. The more intense the winter cooling of the frozen
layer in the annual frost zone and the more rapid the rate of frost heave, the greater the
intensity of uplift forces in piles and foundation walls. The lower the temperature of
permafrost, the higher the bearing capacity and adfreeze strength that can be
developed, the lower the creep deformation rate under footings and in tunnels and
shafts, and the faster the freeze-back of slurried piles. Dynamic response
characteristics of foundations are also a function of temperature. Both natural and
manufactured construction materials experience significant linear and volumetric
changes and may fracture with changes in temperature. Shrinkage cracking of flexible
pavements is experienced in all cold regions. In arctic areas, patterned ground is
widespread, with vertical ice wedges formed in the polygon boundaries. When
underground pipes, power cables, or foundation elements cross shrinkage cracks,
rupture may occur during winter contraction. During summer and fall, expansion of the
warming ground may cause substantial horizontal forces if the cracks have become
filled with soil or ice.
11-2

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Figure 11-1 Frost and permafrost in North America
Engineering problems may also arise from such factors as the difficulty of
excavating and handling ground when it is frozen; soft and wet ground conditions during
thaw periods; surface and subsurface drainage problems; special behavior and handling
requirements for natural and manufactured materials at low temperatures and under
freeze-thaw action; possible ice uplift and thrust action on foundations; condensation on
cold floors; adverse conditions of weather, cost, and sometimes accessibility; in the
more remote locations, limited local availability of materials, support facilities, and labor;
and reduced labor efficiency at low temperatures.
Progressive freezing and frost heave of foundations may also develop
under refrigerated warehouses and other facilities where sustained interior below-
freezing temperatures are maintained. The design procedures and technical guidance
outlined in this chapter may be adapted to the solution of these design problems.
11-2 FACTORS AFFECTING DESIGN OF FOUNDATION
11-2.1 Physiography and Geology. Physiographic and geology details in the
area of the proposed construction are a major factor determining the degree of difficulty
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that may be encountered in achieving a stable foundation. For example, pervious
layers in fine-grained alluvial deposits in combination with copious groundwater supplies
from adjacent higher terra-in may produce very high frost-heave potential, but clean,
free-draining sand and gravel terrace formations of great depth, free of excess ice, can
provide virtually trouble-free foundation conditions.
11-2.2 Temperature. The most important factors contributing to the existence of
adverse foundation conditions in seasonal frost and permafrost regions are cold air
temperatures and the continual changes of temperature between summer and winter,
Mean annual air temperatures usually have to be -17° to -13° C (2° to 8°F) below
freezing for permafrost to be present, although exceptions may be encountered both
above and below this range. Ground temperatures, depths of freeze and thaw, and
thickness of permafrost are the product of many variables including weather, radiation,
surface conditions, exposure, snow and vegetative cover, and insulating or other special
courses. The properties of earth materials that determine the depths to which
freezing-and-thawing temperatures will penetrate below the ground surface under given
temperature differentials over a given time are the thermal conductivity, the volumetric
specific heat capacity, and the volumetric latent heat of fusion. These factors in turn
vary with the type of material, density, and moisture content. Figure 11-2 shows how
ground temperatures vary during the freezing season in an area of substantial seasonal
freezing having a mean annual temperature of 3° C (37°F) (Limestone, Maine), and
Figure 11-3 shows similar data for a permafrost area having a mean annual
temperature of -3° C (26°F) (Fairbanks, Alaska).
For the computation of seasonal freeze or thaw penetration, freezing-and-
thawing indexes are used based upon degree-days relative to 0° C (32°F). For the
average permanent structure, the design indexes should be those for the coldest winter
and the warmest summer in 30 years of record. This criterion is more conservative than
that used for pavements because buildings and other structures are less tolerant of
movement than pavements. It is important to note that indexes found from weather
records are for air about 4.5 ft above the ground; the values at ground surface, which
determine freeze-and-thaw effects, are usually different, being generally smaller for
freezer conditions and larger for thawing where surfaces are exposed to the sun. The
surface index, which is the index determined for temperature immediately below the
surface, is n times the air index, where n is the correction factor. Turf, moss, other
vegetative cover, and snow will reduce the n value for temperatures at the soil surface
in relation to air temperatures and hence give less freeze or thaw penetration for the
same air freezing or thawing index. Values of n for a variety of conditions are given in
UFC 3-130-01.
More detailed information on indexes and their computation, including
maps showing distribution of index values, is presented in UFC 3-130-01.
11-2.3 Foundation Materials. The foundation design decisions may be critically
affected by the foundation soil, ice, and rock conditions.
11-2.3.1 Soils. The most important properties of soils affecting the performance of
engineering structures under seasonal freeze-thaw action are their frost-heaving
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characteristics and their shear strengths on thawing. Criteria for frost susceptibility
based on percentage by weight finer than 0.02 mm are presented in Reference 20.
These criteria have also been developed for pavements. Heave potential at the lower
limits of frost susceptibility determined by these criteria is not zero, although it is
generally low to negligible from the point of view of pavement applications. Applicability
of these criteria to foundation design will vary, depending upon the nature and
requirements of the particular construction. Relative frost-heaving qualities of various
soils are shown in UFC 3-220-10N.
11-2.3.1.1 Permafrost Soils. Permafrost soils cover the entire range of types from
very coarse, boulder strewn glacial drift to clays and organic soils. Strength properties
of frozen soils are dependent on such variables as gradation, density, degree of
saturation, ice content, unfrozen moisture content, temperature, dissolved soils, and
rate of loading. Frozen soils characteristically exhibit creep at stresses as low as 5 to
10 percent of the rupture strength in rapid loading. Typical strength and creep
relationships are described in UFC 3-130-01.
Figure 11-2 Ground Temperatures During Freezing Season in Limestone, Maine
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Figure 11-3 Ground Temperatures During Freezing Season in Fairbanks, Alaska
11-2.3.2 Ice. Ice that is present in the ground in excess of the normal void space is
most obvious as more or less clear lenses, veins or masses easily visible in cores, and
test pits or excavations, but it may also be so uniformly distributed that it is not readily
apparent to the unaided eye. In the annual frost zone, excess ice is formed by the
common ice segregation process, although small amounts of ice may also originate
from filling of shrinkage cracks; ice formations in this zone disappear each summer.
Below the annual frost zone, excess ice in permafrost may form by the same type of ice
segregation process as above, may occur as vertical ice wedges formed by a horizontal
contraction-expansion process, or may be "fossil ice" buried by land slides or other
events. Although most common in fine-grained soils, substantial bodies of excess ice
are not uncommon in permanently frozen clean, granular deposits. The possible
adverse effects of excess ice are discussed in paragraph 11-4.1.1.
11-2.3.3 Rock. Bedrock subject to freezing temperatures should never be
assumed problem-free in absence of positive subsurface information. In seasonal frost
areas, mud seams in bedrock or concentrations of fines at or near the rock surface, in
combination with the ability of fissures in the rock to supply large quantities of water for
ice segregation, frequently cause severe frost heave. In permafrost areas, very
substantial quantities of Ice are often found in bedrock, occurring in fissures and cracks
and along bedding planes.
11-2.4 Water Conditions
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11-2.4.1 Free Water. If free water drawn to developing ice segregation can be
easily replenished from an aquifer layer or from a water table within a few feet of the
plane of freezing, heave can be large. However, if a freezing soil has no access to free
water beyond that contained in voids of the soil immediately at or below the plane of
freezing, frost heave will necessarily be limited.
11-2.4.2 Free Water in Permafrost Areas. In permafrost areas, the supply of
water available to feed growing ice lenses tends to be limited because of the presence
of the underlying impermeable permafrost layer, usually at relatively shallow depths,
and maximum heave may thus be less than under otherwise similar conditions in
seasonal frost areas. However, uplift forces on structures may be higher because of
lower soil temperatures and consequent higher effective tangential adfreeze strength
values.
11-2.4.3 Soil Water Content. The water content of soil exerts a substantial effect
upon the depth of freeze or thaw penetration that will occur with a given surface freezing
or thawing index. Higher moisture contents tend to reduce penetration by increasing
the volumetric latent heat of fusion as well as the volumetric specific heat capacity.
While an increase in moisture also increases thermal conductivity, the affect of latent
heat of fusion tends to be predominant, UFC 3-130-01 contains charts showing thermal
conductivity relationships.
11-2.5 Frost-Heave Forces and Effect Of Surcharge. Frost-heave forces on
structures may be quite large. For some engineering construction, complete prevention
of frost heave is unnecessary and uneconomical, but for most permanent structures,
complete prevention is essential. Under favorable soil and foundation loading
conditions, it may be possible to take advantage of the effect of surcharge to control
heave. It has been demonstrated in laboratory and field experiments that the rate of
frost heaving is decreased by an increase of loading on the freezing plane and that frost
heaving can be completely restrained if sufficient pressure is applied. However, heave
forces normal to the freezing plane may reach more than 958 kPa (10 tons per sq ft).
Detailed information on frost-heaving pressures and on the effect of surcharge is
presented in UFC 3-130-01.
11-2.6 Type of Structure. The type and uses of a structure affect the foundation
design in frost areas as in other places. Applicable considerations are discussed in
UFC 3-130-01.
11-3 SITE INVESTIGATIONS
11-3.1 General. In addition to the needed site investigations and data described
in the manuals for non-frost conditions, design of foundations in areas of significant frost
penetration requires special studies and data because of factors introduced by the
special frost-related site conditions. Detailed site investigation procedures applicable
for arctic and subarctic areas are described in UFC 3-130-02, Chapter 2, and UFC 3-
130-04, Chapter 4, and may be adapted or reduced in scope, as appropriate, in areas of
less severe winter freezing. Methods of terrain evaluation in arctic and subarctic
regions are given in UFC 3-130-01.
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11-3.2 Remote Sensing and Geophysical Investigations. These techniques
are particularly valuable in selection of the specific site location, when a choice is
possible. They can give clues to subsurface frozen ground conditions because of
effects of ground freezing upon such factors as vegetation, land wastage, and soil and
rock electrical and acoustical properties.
11-3.3 Direct Site Investigations. The number and extent of direct site
explorations should be sufficient to reveal in detail the occurrence and extent of frozen
strata, permafrost and excess ice including ice wedges, moisture contents and
groundwater, temperature conditions in the ground, and the characteristics and
properties of frozen materials and unfrozen soil and rock.
11-3.3.1 Bedrock. The need for investigation of bedrock requires special
emphasis because of the possibilities of frost heave or ice inclusions. Bedrock in
permafrost areas should be drilled to obtain undisturbed frozen cores whenever ice
inclusions could affect the foundation design or performance.
11-3.3.2 Discontinuous Permafrost. In areas of discontinuous permafrost, sites
require especially careful exploration and many problems can be avoided by proper site
selection. As an example, the moving of a site 15 to 30 m (50 to 100 ft) from its planned
position may place a structure entirely on or entirely off permafrost, in either case
simplifying foundation design. A location that is partly on, and partly off, permafrost
might involve an exceptionally difficult or costly design.
11.3.3.3 Frozen Soils. Because frozen soils may have compressive strengths as
great as that of a lean concrete and because ice in the ground may be melted by
conventional drilling methods, special techniques are frequently required for subsurface
exploration in frozen materials. Core drilling using refrigerated drilling fluid or air to
prevent melting of ice in the cores provides specimens that are nearly completely
undisturbed and can be subjected to the widest range of laboratory tests. By this
procedure, soils containing particles up to boulder size and bedrock can be sampled,
and ice formations can be inspected and measured. Drive sampling is feasible in frozen
fine-grained soils above about -4° C (25°F) and is often considerably simpler, cheaper,
and faster. Samples obtained by this procedure are somewhat disturbed, but they still
permit ice and moisture content determinations. Test pits are very useful in many
situations. For frozen soils that do not contain very many cobbles and boulders,
truck-mounted power augers using tungsten carbide cutting teeth will provide excellent
service where classification, gradation, and rough ice-content information will, be
sufficient. In both seasonal frost and permafrost areas, a saturated soil condition is
common in the upper layers of soil during the thaw season, so long as there is frozen,
impervious soil still underlying. Explorations attempted during the thaw season are
handicapped and normally require eased boring through the thawed layer. In
permafrost areas, it is frequently desirable to carry out explorations during the colder
part of the year, when the annual frost zone is frozen, than during the summer.
In subsurface explorations that encounter frozen soil, it is important that
the boundaries of frozen and thawed zones and the amount and mode of ice
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strength occurs. In seasonal frost areas, a heaved foundation may or may not return to
its before-heave elevation. Friction on lateral surface or intrusion of softened soil into
the void space below the heaved foundation members may prevent full return.
Successive winter seasons may produce progressive upward movement. Therefore,
when the soils within the maximum depth of seasonal frost penetration are
frost-susceptible, foundations in seasonal frost areas should be supported below the
annual frost zone, using conventional foundation elements protected against uplift
caused by adfreeze grip and against frost overturning or sliding forces, or the structure
should be placed on compacted non-frost-susceptible fill designed to control frost
effects (Figure 11-4).
11-4.1.2 Foundations in Permafrost Areas. Design on permafrost areas must
cope with both the annual frost zone phenomena described in paragraph 11-4.1 and
those peculiar to permafrost.
11-4.1.2.1 Permafrost Foundations not Adversely Affected by Thaw. Whenever
possible, structures in permafrost areas should be located on clean,
non-frost-susceptible sand or gravel deposits or rock that is free of ground ice or of
excess interstitial ice, which would make the foundation susceptible to settlement on
thaw. Such sites are ideal and should be sought whenever possible. Foundation
design under these conditions can be basically identical with temperate zone practices,
even though the materials are frozen below the foundation support level, as has been
demonstrated in Corps of Engineers construction in interior Alaska. When conventional
foundation designs are used for such materials, heat from the structure will gradually
thaw the foundation to progressively greater depths over an indefinite period of years. In
5 years, for example, thaw may reach a depth of 40 ft. However, if the foundation
materials are not susceptible to settlement on thaw, there will be no effects on the
structure from such thaw. The possible effect of earthquakes or other dynamic forces
after thawing should be considered.
11-4.1.2.2 Permafrost Foundations Adversely Affected by Thaw. When
permafrost foundation materials containing excess ice are thawed, the consequences
may include differential settlement, slope instability, development of water-filled surface
depressions that serve to intensify thaw, loss of strength of frost loosened foundation
materials under excess moisture conditions, development of underground uncontrolled
drainage channels in permafrost materials susceptible to bridging or piping, and other
detrimental effects. Often, the results may be catastrophic. For permafrost soils and
rock containing excess ice, design should consider three alternatives, as indicated in
Figure 11-4: (1) maintenance of stable thermal regime, (2) acceptance of thermal
regime changes and (3) modification of foundation conditions prior to construction.
These approaches are discussed in UFC 3-130-01. Choice of the specific foundation
type from among those indicated in Figure 11-4 can be made on the basis of cost and
performance requirements after the development of details to the degree needed for
resolution.
11-4.2 Foundation Freeze and Thaw and Techniques for Control. Detailed
guidance for foundation thermal computations and for methods of controlling freeze-
and-thaw penetration is presented in UFC 3-130-01.
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11-4.2.1 Design Depth of Ordinary Frost Penetration. For average permanent
structures, the depth of frost penetration assumed for design in situations not affected
by heat from a structure, should be that which will occur in the coldest year in 30 years.
For a structure of a temporary nature or otherwise tolerant of some foundation
movement, the depth of frost penetration in the coldest year in 10 years or even that in
the mean winter may be used, as may be most applicable. The design depth should
preferably be based on actual measurements or on computations if measurements are
not available. When measurements are available, they will almost always need to be
adjusted by computations to the equivalent of the freezing index selected as the basis
for design, as measurements will seldom be available for a winter having a severity
equivalent to that value.
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Figure 11-4 Design Alternatives
The frost penetration can be computed using the design freezing index
and the detailed guidance given in UFC 3-130-01. For paved areas kept free of snow,
approximate depths of frost penetration may be estimated from UFC 3-130-01, by
entering the appropriate chart with the air freezing index. A chart is also presented in
UFC 3-130-01, from which approximate depths of frost penetration may be obtained for
a variety of surface conditions, using the air freezing index in combination with the
appropriate surface index/air correction factor (n-factor).
In the more developed parts of the cold regions, the building codes of
most cities specify minimum footing depths, based on many years of local experience;
these depths are invariably less than the maximum observed frost penetrations. The
code values should not he assumed to represent actual frost penetration depths. Such
local code values have been selected to give generally suitable results for the types of
construction, soil moisture, density, and surface cover conditions, severity of freezing
conditions, and building heating conditions that are common in the area. Unfortunately,
the code values may be inadequate or inapplicable under conditions that differ from
those assumed in formulating the code, especially for unheated facilities, insulated
foundations, or especially cold winters. Building codes in the Middle and North Atlantic
States and Canada frequently specify minimum footing depths that range from 1 to 1.5
m (3 to 5 ft). If frost penetrations of this order of magnitude occur with fine silt and
clay-type soils, 30 to 100 percent greater frost penetration may occur in well-drained
gravels under the same conditions. With good soil data and knowledge of local
conditions, computed values for ordinary frost penetration, unaffected by building heat,
may be expected to be adequately reliable, even though the freezing index may have to
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be estimated from weather data from nearby stations. In remote areas, measured frost
depths may be entirely unavailable.
11-4.2.2 Design Depth of Ordinary Thaw Penetration. Estimates of seasonal
thaw penetration in permafrost areas should be established on the same statistical
measurement bases as outlined in paragraph 11-4.2.1 above for seasonal frost
penetration. The air thawing index can be converted to a surface thawing index by
multiplying it by the appropriate thawing conditions n-factor from UFC 3-130-01 and the
thaw penetration can then be computed using the detailed guidance given in that
criteria. Approximate values of thaw penetration may also be estimated from a chart of
the air thawing index versus the depth of thaw in UFC 3-130-01. Degradation of
permafrost will result if the average annual depth of thaw penetration exceeds the
average annual depth of frost penetration.
11-4.2.3 Thaw or Freeze Beneath Structures. Any change from natural
conditions, which results in a warming of the ground beneath a structure, can result in
progressive lowering of the permafrost table over a period of years. Heat flow from a
structure into underlying ground containing permafrost can only be ignored as a factor in
the long-term structural stability when the nature of the permafrost is such that no
settlement or other adverse effects will result. The source of heat may he not only the
building heat but also the solar radiation, underground utilities, surface water, and
groundwater flow. UFC 3-130-01 provides guidance on procedures for estimating the
depth of thaw under a heated building with time.
The most widely-employed, effective and economical, means of
maintaining a stable thermal regime under a heated structure, without degradation of
permafrost, is by use of a ventilated foundation. Under this scheme, provision is made
for the circulation of cold air between the insulated floor and the underlying ground. The
same scheme can be used for the converse situation of a refrigerated facility supported
on unfrozen ground. The simplest way of providing foundation ventilation is by
providing an open space under the entire building, with the structure supported on
footings or piling. For heavier floor loadings, ventilation ducts below the insulated floor
may be used. Experience has shown that ventilated foundations should be so elevated,
sloped, oriented, and configured as to minimize possibilities for accumulation of water,
snow, ice, or soil in the ducts. Guidance in the thermal analysis of ventilated
foundations, including the estimation of depths of summer thaw in supporting materials
and design to assure winter refreezing, is given UFC 3-130-01.
Natural or forced circulation thermal piles or refrigeration points may also
be used for overall foundation cooling and control of permafrost degradation.
11-4.2.4 Foundation Insulation. Thermal insulation may be used in foundation
construction in both seasonal frost and permafrost areas to control frost penetration,
frost heave, and condensation, and to conserve energy, provide comfort, and enhance
the effectiveness of foundation ventilation. Unanticipated loss of effectiveness by
moisture absorption must be avoided. Cellular glass should not be used where it will be
subject to cyclic freezing and thawing in the presence of moisture. Insulation thickness
and placement may be determined by the guidance given in UFC 3-130-01.
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11-4.2.5 Granular Mats. In areas of significant seasonal frost and permafrost, a
mat of non-frost-susceptible granular material may be used to moderate and control
seasonal freeze-and-thaw effects in the foundation, to provide drainage under floor
slabs, to provide stable foundation support, and to provide a dry, stable working
platform for construction equipment and personnel. Seasonal freezing-and-thawing
effects may be totally or partially contained within the mat. When seasonal effects are
only partially contained, the magnitude of seasonal frost heave is reduced through both
the surcharge effect of the mat and the reduction of frost penetration into underlying
frost-susceptible soils. UFC 3-130-01 provides guidance in the design of mats.
11-4.2.6 Solar Radiation Thermal Effects. The control of summer heat input from
solar radiation is very important in foundation design in permafrost areas. Corrective
measures that may be employed include shading, reflective paint or other surface
material, and sometimes live vegetative covering. In seasonal frost areas, it may
sometimes be advantageous to color critical surfaces black to gain maximum effect of
solar heat in reducing winter frost problems. UFC 3-130-01 provides guidance on the
control of solar radiation thermal effects.
11-4.3 Control of Movement and Distortion. The amount of movement and
distortion that may be tolerated in the support structure must be established and the
foundation must be designed to meet these criteria. Movement and distortion of the
foundation may arise from seasonal upward, downward, and lateral displacements, from
progressive settlement arising from degradation of permafrost or creep deflections
under load, from horizontal seasonal shrinkage and expansion caused by temperature
changes, and from creep flow, or slide of material on slopes. Heave may also occur on
a non-seasonal basis if there is progressive freezing in the foundation, as under a
refrigerated building or storage tank. If the subsurface conditions, moisture availability,
frost penetration, imposed loading, or other factors vary in the foundation area, the
movements will be non-uniform. Effects on the foundation and structure may include
various kinds of structural damage, jamming of doors and windows, shearing of utilities,
and problems with installed equipment.
11-4.3.1 Frost-Heave and Thaw-Settlement Deformations. Frost heave acts in
the same direction as the heat flow or perpendicular to the freezing plane. Thus, a slab
on a horizontal surface will be lifted directly upward, but a vertical retaining wall may
experience horizontal thrust. Foundation members, such as footings, walls, piles, and
anchors, may also be gripped on their lateral surfaces and heaved by frost forces acting
in tangential shear. Figure 11-5 shows an example of frost-heave forces developed in
tangential shear on timber and steel pipe piles restrained against upward movement.
In rivers, lakes, or coastal water bodies, foundation members, to which
floating ice may adhere, may also be subject to important vertical forces as water levels
fluctuate.
11-4.3.2 Controlling Frost Heave. Among methods that can be used to control
detrimental frost action effects are placing non-frost-susceptible soils in the depth
subject to freezing to avoid frost heave or thrust; providing sufficient embedment or
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other anchorage to resist movement under the lifting forces; providing sufficient loading
on the foundation to counterbalance upward forces: isolating foundation members from
heave forces; battering tapering members within the annual frost zone to duce
effectiveness of heave grip; modifying soil frost susceptibility; in seasonal frost areas
only, taking advantage of natural heat losses from the facility to minimize adfreeze and
frost heave; or cantilevering building attachments, e.g., porches and stairs, to its main
foundation.
11-4.3.3 Permafrost. In permafrost areas, movement and distortion caused by
thaw of permafrost can be extreme and should be avoided by designing for full and
positive thermal stability whenever the foundation would be adversely affected by thaw,
If damaging thaw settlement should start, a mechanical refrigeration system may have
to be installed in the foundation or a program of continual jacking may have to be
adopted for leveling of the structure. Discontinuance or reduction of building heat can
also be effective. Detailed guidance is given in UFC 3-130-01.
11-4.3.4 Creep Deformation. Only very small loads can be carried on the
unconfined surface of ice-saturated frozen soil without progressive deformation. The
allowable long-term loading increases greatly with depth but may be limited by
unacceptable creep deformation well short of the allowable stress level determined from
conventional short-term test. Present practice is to use large footings with low unit
loadings; support footings on mats of well-drained non-frost-susceptible granular
materials, which reduce stresses on underlying frozen materials to conservatively low
values; or place foundations at sufficient depth in the ground so that creep is effectively
minimized. Pile foundations are designed to not exceed sustainable adfreeze bond
strengths. In all cases, analysis is based on permafrost temperature at the warmest
time of the year.
11-4.4 Vibration Problems and Seismic Effects. Foundations supported on
frozen ground may be affected by high stress-type dynamic loadings, such as shock
loadings from high-yield explosions, by lower stress pulse-type loadings as from
earthquakes or impacts, or by relatively low-stress, relatively low-frequency,
steady-state vibrations. In general, the same procedures used for non-frozen soil
conditions are applicable to frozen soils. Design criteria are given in UFC 3-220-03A
and UFC 3-220-09. These criteria also contain references to sources of data on the
general behavior and properties of non-frozen soils under dynamic load and discuss
types of laboratory and field tests available. However, design criteria, test techniques,
and methods of analysis are not yet firmly established for engineering problems of
dynamic loading of foundations. Therefore, the senior engineer of the organization
should be notified upon initiation of design and should participate in establishing criteria
and approach and in planning field and laboratory tests.
All design approaches require knowledge of the response characteristics
of the foundation materials, frozen or non-frozen, under the particular load involved. As
dynamic loadings occur in a range of stresses, frequencies, and types (shock, pulse,
steady-state vibrations, etc.), and the response of the soil varies depending upon the
load characteristics, the required data must be obtained from tests that produce the
same responses as the actual load. Different design criteria are used for the different
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types of dynamic loading, and different parameters are required. Such properties as
moduli, damping ability, and velocity of propagation vary significantly with such factors
as dynamic stress, strain, frequency, temperature, and soil type and condition. UFC 3-
130-01 discusses these properties for frozen ground.
11-4.5 Design Criteria for Various Specific Engineering Features. In addition
to the basic considerations outlined in the preceding paragraphs of this chapter, the
design of foundations for frost and permafrost conditions requires application of detailed
criteria for specific engineering situations. Guidance for the design of various specific
features, construction consideration, and monitoring of performance of foundation is
presented in UFC 3-130-01.
Figure 11-5 Heave Force Test
(Average tangential Adfreeze bond stress versus time, and timber and steel pipe piles with silt-water
slurry in dry excavated holes. Piles were installed within annual frost zone only, over permafrost, to
depths from ground surface of 1.1 to 2 meters (3.6 to 6.5 feet).)
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force, e.g., Q = Qo sin (ωt), in which Qo is the amplitude of the exciting force, ω = 2πfo is
the angular frequency (radians per second) with fo the exciting frequent (cycles per
second), and t is time in seconds.
lf the model is oriented as shown in the insert in figure 12-2(a), motions
will occur in the vertical or z direction only, and the system has one degree of freedom
(one coordinate direction (z) is needed to describe the motion). The magnitude of
dynamic vertical motion, Az, decade upon the magnitude of the external excitation, Q,
the nature of Qo, the frequency, fo, and the system parameter m. c, and k. These
parameters are customarily combined to describe the “natural frequency” as follows:
fn = 1/(2xπ)x(k/m)1/2
(12-1)
and the “damping ratio” as
D = c/2x (k/m) -1/2
(12-2)
Figure 12-2(a) shows the dynamic response of the system when the
amplitude of the exciting fore. Qo, is constant. The abscissa of the diagram is the
dimensionless ratio of exciting frequency, fo, divided by the natural frequency, fn, in
equation (12-1). The ordinate is the dynamic magnification factor, Mz which is the ratio
of A, to the static displacement, Az = (Qo/k). Different response curves correspond to
different values of D.
Figure 12-2(b) is the dynamic response of the system when the exciting
force is general by a rotating max, which develops:
Qo = mo(ē)4π2
fo
2
(12-3)
where
me = the total rotating mass
ē = the eccentricity
fo = the frequency of oscillation, cycles per second
The ordinate Mż (fig 12-2(b)) relates the dynamic displacement, Az, to me ē/m. The
peak value of the response curve is a function of the damping ratio and is given by the
following expression:
Me(max) or Mż = 1/(2D)x(1 – D2
) -1/2
(12-4)
2D w 1 – D2
For small values of D, this expression becomes 1/2D. These peak values occur at
frequency ratios of
__fo__ = w 1 – D2
(12-5)
fn
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or
__fo__ = ___1____ (12-6)
fn w 1 – 2D2
Figure 12-1 Response Spectra for Vibration Limits
(Courtesy of F. E. Richart, Jr., J. R. Hall, Jr. and R. D. Woods,
Vibrations of Soils and Foundations,
1970. p 316. Reprinted by permission of Prentice-
Hall, Inc., Englewood Cliffs, N. J.)
12-1.3 Foundations on Elastic Soils
12-1.3.1 Foundations on Elastic Half-Space. For very small deformations,
assume soils to be elastic materials with properties as noted in UFC 3-220-09.
Therefore, theories describing the behavior of rigid foundations resting on the surface of
a semi-infinite, homogeneous, isotropic elastic body have been found useful for study of
the response of real footings on soils. The theoretical treatment involves a circular
foundation of radius, ro, on the surface of the ideal half-space. This foundation has six
degrees of freedom: (1-3) translation in the vertical (z) or in either of two horizontal (x
and y) directions; (4) torsional (yawing) rotation about the vertical (z) axis; or (5-6)
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rocking (pitching) rotation about either of the two horizontal (x and y) axes. These
vibratory motions are illustrated in figure 12-3.
A significant parameter in evaluating the dynamic response in each type of
motion is the inertia reaction of the foundation. For translation, this is simply the mass,
m = (W/g), whereas in the rotational modes of vibration, it is represented by the mass
moment of inertia about the axis of rotation. For torsional oscillation about the vertical
axis, it is designated as Io, whereas for rocking oscillation, it is Iψ (for rotation about the
axis through a diameter of the base of the foundation). If the foundation is considered
to be a right circular cylinder of radius, ro, height, h, and unit weight, γ, expressions for
the mass and mass moments of inertia are as follows:
m = _π ro
2
hγ_ (12-7)
g
Iθ = _π ro
4
hγ_ (12-8)
2g
Iψ = _π ro
2
hγ_ o __ro
2
__ + ___h2
___ p
g 4 3 (12-9)
Theoretical solutions describe the motion magnification factors Mz or Mż,
for example, in terms of a “mass ratio” Bz and a dimensionless frequency factor ao.
Table 12-1 lists the mass ratios, damping ratios, and spring constants corresponding to
vibrations of the rigid circular footing resting on the surface of an elastic semi-infinite
body for each of the modes of vibration. Introduce these quantities into equations given
in paragraph 12-1.2 to compute resonant frequencies and amplitudes of dynamic
motions. The dimensionless frequency, ao, for all modes of vibration is given as follows:
ao = _ 2π fo ro__ = ω ro w(ρ/G)
Vs (12-10)
The shear velocity, Vs, in the soil is discussed in paragraph 17-5.
Figure 12-4 shows the variation of the damping ratio, D, with the mass
ratio, B, for the four modes of vibration. Note that D is significantly lower for the rocking
mode than for the vertical or horizontal translational modes. Using the expression
meters = 1/(2D) for the amplitude magnification factor and the appropriate Dψ from
figure 12-4, it is obvious that metersψ can become large. For example, if Bψ = 3, the Dψ
= 0.02 and metersψ = 1/(2 x 0.02) = 25.
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Table 12-1 Mass Ratio, Damping Ratio, and Spring Constant for Rigid Circular
Footing on the Semi-Infinite Elastic Body
Figure 12-5 Equivalent Damping Ratio for Oscillation of Rigid Circular Footing on
Elastic Half-Space
12-1.3.2 Effects of Shape Foundation. The theoretical solutions described above
treated a rigid foundation with a circular contact surface bearing against the elastic half-
space. However, foundations are usually rectangular in plan. Rectangular footings may
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be converted into an equivalent circular footing having a radius, ro, determined by the
following expressions:
(12-10)
(12-11)
(12-12)
In equations (12-10), (12-11), and (12-12), 2c is the width of the rectangular foundation
(along the axis of rotation for rocking), and 2d is the length of the foundation (in the
plane of rotation for rocking). Two values of ro are obtained for rocking about both x and
y axes.
12-1.3.3 Computations. Figure 12-5 presents examples of computations for
vertical motions (Example 1) and rocking motions (Example 2).
12-1.3.4 Effect of Embedment. Embedment of foundations a distance d below
the soil surface may modify the dynamic response, depending upon the soil-foundation
contact and the magnitude of d. If the soil shrinks away from the vertical faces of the
embedded foundation, no beneficial effects of embedment may occur. If the basic
evaluation of foundation response is based on a rigid circular footing (of radius ro) at the
surface, the effects of embedment will cause an increase in resonant frequency and a
decrease in amplitude of motion and the embedment ratio d/ro.
The influence of embedment on coupled rocking and sliding vibrations
depends on the ratio Bψ/Bx (table12-1). For Bψ/Bx ~= 3.0, the increase in natural
frequency due to embedment may be as much as (1+0.5 d/ro). The decrease in
amplitude is strongly dependent upon the soil contact along the vertical face of the
foundation, and each case should be evaluated on the basis of local soil and
construction conditions.
For vertical vibrations, both analytical and experimental results indicate an
increase in the static spring constant with an increase in the static spring constant with
an increase in embedment depth. Embedment of the circular footing a distance d/ro ≤
1.0 produces an increase in the embedded spring constant kxd which is grater than kz,
(table 12-1) by kzd/kz ≅ (1+0.6 d/ro). An increase in damping also occurs, e.g., Dzd/Dz ≅
(1+0.6 d/ro). These two approximate relations lead to an estimate of the reduction in
amplitude of motion because of embedment from Azd/Az = 1/Dzd/Dz x kzd/kz). This
amount of amplitude reduction requires complete soil adhesion at the vertical face, and
test data have often indicated less effect of embedment. Test data indicate that the
resonant frequency may be increased by a factor up to (1 + 0.25 d/ro) because of
embedment.
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12-1.3.5 Effect of Finite Thickness Of Elastic Layer. Deposits of real soils are
seldom homogeneous to significant depths; thus theoretical results based on the
response of a semi-infinite elastic media must be used with caution. When soil layers
are relatively thin, with respect to foundation dimensions, modifications to the theoretical
half-space analyses must be included.
Generally, the effect of a rigid layer underlying a single elastic layer of
thickness, H, is to reduce the effective damping for a foundation vibrating at the upper
surface of the elastic layer. This condition results from the reflection of wave energy
from the rigid base back to the foundation and to the elastic medium surrounding the
foundation. For vertical or torsional vibrations or a rigid circular foundation resting on
the surface of the elastic layer, it has been established that a very large amplitude of
resonant vibrations can occur if
In equation (12-13), Vs is the shear wave velocity in the elastic layer and fo
is the frequency of footing vibrations. When the conditions of equation (12-4) occur, the
natural frequency (equation (12-1)) becomes the important design criterion because at
that frequency excessive dynamic motion will occur. To restrict the dynamic oscillation
to slightly larger than the static displacement, the operating frequency should be
maintained at one half, or less, of the natural frequency (figure 12-2).
The relative thickness (expressed by H/ro) also exerts an important
influence on foundation response. If H/ro is greater than about 8, the foundation on the
elastic layer will have a dynamic response comparable to that for a foundation on the
elastic half-space. For H/ro < 8, geometrical damping is reduced, and the effective
spring constant is increase. The values of spring constant, k, in table 12-1 are taken as
reference values, and table 12-2 indicates the increase in spring constant associated
with a decrease in thickness of the elastic layer. Values of the increase in spring
constant for sliding and for rocking modes of vibration will tend to fall between those
given for vertical and torsion for comparable H/ro conditions.
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Figure 12-5 Examples of Computations for Vertical and Rocking Motions
12-1.3.6 Coupled Modes of Vibration. In general, vertical and torsional vibrations
can occur independently without causing rocking or sliding motions of the foundation.
To accomplish these uncoupled vibrations, the line of action of the vertical force must
pass through the center of gravity of the mass and the resultant soil reaction, and the
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exciting torque and soil reaction torque must be symmetrical about the vertical axis of
rotation. Also, the center of gravity of the foundation must lie on the vertical axis of
torsion.
When horizontal or overturning moments act on a block foundation, both
horizontal (sliding) and rocking vibrations occur. The coupling between these motions
depends on the height of the center of gravity of the machine-foundation about the
resultant soil reaction. Details of a coupled rocking and sliding analysis are given in the
example in figure 12-6.
A “lower bound” estimate of the first mode of coupled rocking and sliding
vibrations can be obtained from the following:
(12-14)
In equation (12-14), the resonant frequencies in the sliding x and rocking w motions can
be determined by introducing values from table 12-1 into equations (12-1) and (12-5).
(Note that equation (12-14) becomes less useful when Dz is greater than about 0.15).
The first mode resonant frequency is usually most important from a design standpoint.
12-1.3.7 Examples. Figure 12-5, Example 1, illustrates a procedure for design of a
foundation to support machine-producing vertical excitations. Figure 12-5, Example 2,
describes the analysis of uncouple horizontal and rocking motion for a particular
foundation subjected to horizontal excitations. The design procedure of Example 1 is
essentially an iterative analysis after approximate dimensions of the foundation have
been established to restrict the static deflection to a value comparable to the design
criterion.
• Figure 12-5, Example 1, shows that relatively high values of damping ratio D are
developed for the vertical motion of the foundation, and Example 2 illustrates that
the high damping restricts dynamic motions to values slightly larger than static
displacement caused by the same force. For Example 2, establishing the static
displacement at about the design limit value leads to satisfactory geometry of the
foundation.
• Example 2 (Figure 12-5) gives the foundation geometry, as well as the analysis
needed to ascertain whether the design criterion is met. It is assumed that the
400-pound horizontal force is constant at all frequencies and that a simple
superposition of the single-degree-of-freedom solutions for horizontal translation
and rocking will be satisfactory. Because the horizontal displacement is
negligible, the rocking motion dominates, with the angular rotation at resonance
amounting to (metersψ x ψs) or Aψ = 5.6 x 0.51 x 10-6 = 2/85 x 10-6 radians. By
converting this motion to horizontal displacement at the machine centerline, it is
found that the design conditions are met.
• Figure 12-6, the foundation of Example 2 (figure 12-5), is analyzed as a coupled
system including both rocking and sliding. The response curve for angular
rotation shows a peak motion of Aψ = 2.67 x 10-6 radians, which is comparable to
the value found by considering rocking alone. The coupled dynamic response of
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any rigid foundation, e.g., a radar tower, can be evaluated by the procedure
illustrated in Figure 12-6.
Table 12-2 Values of kL/L for Elastic Layer (k from Table 12-1)
meters/ro
Vertical
Torsion
0.5
5.0
---
1.0
2.2
1.07
2.0
1.47
1.02
4.0
1.23
1.009
8.0
1.10
---
∞
1.0
1.0
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Figure 12-6 Coupled Rocking and Sliding Motion of Foundation
12-1.4 Wave Transmission, Attenuation, and Isolation. Vibrations are
transmitted through soils by stress waves. For most engineering analyses, the soil may
be treated as an ideal homogeneous, isotropic elastic material to determine the
characteristics of the stress waves.
12-.1.4.1 Half-Space. Two types of body waves may be transmitted in an ideal
half-space, compression (P-) waves and shear (S-) waves; at the surface of the half-
space, a third wave known as the Rayleigh (R-) wave or surface wave will be
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transmitted. The characteristics that distinguish these three waves are velocity, wave
front geometry, radiation damping, and particle motion. Figure 12-7 shows the
characteristics of these waves as they are generated by a circular footing undergoing
vertical vibration on the surface of an ideal half-space with u= 0.25. The distance from
the footing to each wave in figure 12-7 is drawn in proportion to the velocity of each
wave. The wave velocities can be computed from the following:
(12-17)
(12-15)
(12-16)
where
The P- and S-waves propagate radially outward from the source along
hemispherical wave fronts, while the R-wave propagates outward along a cylindrical
wave front. All waves encounter an increasingly larger volume of material as they travel
outward, thus decreasing in energy density with distance. This decrease in energy
density and its accompanying decrease in displacement amplitude are called
geometrical damping or radiation damping.
The particle motions are as follows: for the P- wave, a push-pull motion in
the radial direction; for the S-wave, a transverse motion normal to the radial direction;
and for the R-wave, a complex motion, that varies with depth and occurs in a vertical
plane containing a radius. At the surface, R-wave particle motion describes a
retrograde ellipse. The shaded zones along the wave fronts in figure 12-7 represent the
relative particle amplitude as a function of inclination from vertical.
12-1.4.2 Layered Media. In a layered medium, the energy transmitted by a body
wave splits into four waves at the interface between layers. Two waves are reflected
back into the first medium, and two waves are transmitted or refracted into the second
medium. The amplitudes and directions of all waves can be evaluated if the properties
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of both media and the incident angle are known. If a layer containing a lower modulus
overlies a layer with a higher modulus within the half-space, another surface wave,
known as a Love wave, will occur. This wave is a horizontally oriented S-wave whose
velocity is between the S-wave velocity of the layer and of the underlying medium.
The decay or attenuation of stress waves occurs for two reasons:
geometric or radiation damping, and material or hysteretic damping. An equation
including both types of damping is the following:
(12-18)
r1
A2 = A1
r2
C
exp [-α(r2 – r1)]
where
A2 = desired amplitude at distance r2
A1 = known or measured amplitude at radial distance r1 from vibration source
C = constant, which describes geometrical damping
= 1 for body (P- or S-) waves
= 0.5 for surface or R-waves
α = coefficient of attenuation, which describes material damping
12-1.4.3 Isolation. The isolation of certain structures or zones from the effects of
vibration may sometimes be necessary. In some instances, isolation can be
accomplished by locating the site at a large distance from the vibration source. The
required distance, r2, is calculated from equation (12-18). In other situations, isolation
may be accomplished by wave barriers. The most effective barriers are open or void
zones like trenches or rows of cylindrical holes. Somewhat less effective barriers are
solid or fluid-filled trenches or holes. An effective barrier must be proportioned so that
its depth is at least two-thirds the wavelength of the incoming wave. The thickness of
the barrier in the direction of wave travel can be as thin as practical for construction
considerations. The length of the barrier perpendicular to the direction of wave travel
will depend upon the size of the zone to be isolated but should be no shorter than two
times the maximum plan dimension of the structure or one wavelength, whichever is
greater.
12-1.5 Evaluation of S-Wave Velocity in Soils. The key parameter in a
dynamic analysis of a soil-foundation system is the shear modulus, G. The shear
modulus can be determined in the laboratory or estimated by empirical equations. The
value of G can also be computed by the field-measured S-wave velocity and equation
(12-16).
12-1.5.1 Modulus at Low Strain Levels. The shear modulus and damping for
machine vibration problems correspond to low shear-strain amplitudes of the order of 1
to 3 x 10-4 percent. These properties may be determined from field measurements of
the seismic wave velocity through soil or from special cyclic laboratory tests.
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Figure 12-7 Distribution of Displacement Waves from a Circular Footing on the
Elastic Half-Space
Table 12-3 Attenuation Coefficients for Earth Materials
Materials α (l/ ft) @ 50 Hza
Sand
Loose, fine
Dense, fine
0.06
0.02
Clay
Silty (loess)
Dense, dry
0.06
0.003
Rock
Weathered volcanic
Competent marble
0.02
0.00004
a
α is a function of frequency. For other frequencies, f, compute αf = (f/50) x α50
Source: U.S. Army Corps of Engineers
12-1.5.2 Field Wave Velocity Tests. S-wave velocity tests are preferable made in
the field. Measurements are obtained by inducing a low-level seismic excitation at one
location and measuring directly, the time required for the induced S-wave to travel
between the excitation and pickup unit. Common tests, such as uphole, downhole or
crosshole propagation, are described in geotechnical engineering literature.
A problem in using seismic methods to obtain elastic properties is, that
any induce elastic pulse (blast, impact, etc.) develops three wave types previously
discussed, i.e., P-, S-, and R-waves. Because the velocity of all seismic waves is
hundreds of feet per second and the pickup unit detects all three wave pulses plus any
random noise, considerable expertise is required to differentiate between the time of
arrival of the wave of interest and the other waves. The R-wave is usually easier to
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identify (being slower, it arrives last; traveling near the surface, it contains more relative
energy). Because R- and S-wave velocities are relatively close, the velocity of the R-
wave is frequently used in computations for elastic properties.
• Because amplitudes in seismic survey are very small, the computed shear and
Young’s moduli are considerably larger than those obtained from conventional
laboratory compression tests.
• The shear modulus, G, may be calculated from the S- (approximately the R-
wave) wave velocity as follows:
(12-19)
G = pVs
2
where
p = y/32.2 = mass density of soil using wet or total unit weight
Vs = S-wave velocity (or R-wave), feet per second
This equation is independent of Poisson’s ratio. The Vs value is taken as
representative to a depth of approximately one-half wavelength. Alternatively, the shear
modulus can be computed from the P-wave velocity and Poisson’s ratio from:
(12-20)
p(1 - 2µ)
G =
2(1 - µ)
Vp
2
The use of this equation is somewhat limited because the velocity of a P-wave is
approximately 5000 feet per second (approximately the velocity in many soils) and
Poisson’s ratio must be estimated. For saturated or near saturated soils, µ -> 0.5. The
theoretical variation of the ratio Vs/Vp with u is shown in figure 12-8.
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Figure 12-8 Theoretical Relation Between Shear Velocity Ratio Vp/Vs and
Poisson’s Ratio
12-1.5.3 Laboratory Measurement of Dynamic Stress-Strain Properties. Low
shear-strain amplitude, e.g., less than 10-2 percent, shear modulus data may be
obtained from laboratory tests and usually involves applying some type of high-
frequency forced vibration to a cylindrical sample of soil and measuring an appropriate
response. Some types of tests allow the intensity level of the forced vibration to be
varied, thus yielding moduli at different shear strains.
High strain-level excitation, e.g., 0.01 to 1.0 percent, may be achieved by
low-frequency, cyclic loading triaxial compression tests on soil samples. The modulus,
damping and strain level for a particular test are calculated directly from the sample
response data. The usual assumption for calculating the modulus and damping from
forced cyclic loading tests on laboratory samples is that at any cyclic strain amplitude
the soil behaves as a linear elastic, viscous, damped material. A typical set of results
may take the form of a hysteresis loop as shown in Figure 12-9. Either shear or normal
stress cyclic excitation may be use. The shear modulus is calculated from the slope of
the peak-to-peak secant line. The damping is computed from the area of the hysteresis
loop, and the strain level is taken as the single-amplitude (one-half the peak-to-peak
amplitude or origin to peak value) cyclic strain for the condition during that cycle of the
test. Note that the equations for modulus and damping shown in Figure 12-9 assume
the soil behaves as an equivalent elastic viscous, dampened material, which is linear
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within the range of strain amplitude specified. This assumption is usually made in most
soil dynamics analyses because of the low-vibration amplitudes involved. If the cyclic
hysteresis loops are obtained from triaxial test specimens, the resulting modulus will be
the stress-strain modulus, E. If the tests involve simple shear or torsion shear such that
modulus will be the shear modulus, G. In either case, the same equations apply.
The shear modulus, G, can be computed from the stress strain modulus
and Poisson’s ratio as follows:
(12-21)
E
G =
2(1 + µ)
The shear strain amplitude, Ae, may be computed from the axial strain amplitude, e, and
Poisson’s ratio as follows:
(12-22)
Ae = ε(1 + µ)
For the special case of saturated soils, Poisson’s ratio is
0.5, which leads to the following:
G = E/3
Ae = 1.5ε
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Figure 12-9 Idealized Cyclic Stress-Strain Loop for Soil
12-1.5.4 Correlations. Empirical correlations from many sets of data have
provided several approximate methods for estimating the S-wave velocity and shear
modulus for soils corresponding to low-strain excitation. For many undisturbed
cohesive soils and sands: (12-23)
1230(21973 – e) 2
G =
1 + e
(OCR)η
(Ó0)0.5
(pounds per square inch)
where
e = void ratio
η = empirical constant, which depends on the PI of cohesive soils (table
12-4); For sands, PI = 0
and η = 0, so OCR term reduces to 1.0. For clays, the maximum
value is η = 0.5 for PI ≥ 100.
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Ó0 = 1/3 (Ó1 + Ó2 + Ós) = mean normal effective stress, pounds per
square inch
(1) For sands and gravels, calculate the low-strain shear modulus as follows:
G = 1000(Ks)(Ó0)0.5
(pounds per square foot) (12-24)
where
K2 = empirical constant (table 12-5)
= 90 to 190 for dense sand, gravel, and cobbles with little clay
Ó0 = mean normal effective stress as in equation (12-23) (but in units of
pounds per square foot)
(2) For cohesive soils as clays and peat, the shear modulus is related to Su as
follows:
G = K2su (12-25)
For clays, K2 ranges from 1500 to 3000. For peats, K2 ranges from 150 to 160
(limited data base).
(3) In the laboratory, the shear modulus of soil increases with time even when all
other variables are held constant. The rate of increase in the shear modulus is
approximately linear as a function of the log of time after an initial period of about
1000 minutes. The change in shear modulus, ∆G, divided by the shear modulus
at 1000 minutes, G1000, is called the normalized secondary increase. The
normalized secondary increases ranges from nearly zero percent per log for
sensitive clays. For good correlation between laboratory and field measurements
of shear modulus, the age of the in situ deposit must be considered, and a
secondary time correction applies to the laboratory data.
12-1.5.5 Damping in Low Strain Levels. Critical damping is defined as
cc = 2√km (12-26)
Where k is the spring of vibrating mass and m represents mass undergoing vibration
(W/g). Viscous damping of all soils at low strain-level excitation is generally less than
about 0.01 percent of critical damping for most soils or:
D = c/cc ≤ 0.05 (12-27)
It is important to note that this equation refers only to material damping, and not to
energy loss by radiation away from a vibrating foundation, which may also be
conveniently expressed in terms of equivalent viscous damping. Radiation damping in
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machine vibration problems is a function of the geometry of the problem rather than of
the physical properties of the soil.
Table 12-4 Values of Constant η Used with Equation (12-23) to Estimate
Cyclic Shear Modulus at Low Strains
Plasticity Index K
0 0
20 0.18
40 0.30
60 0.41
80 0.48
≥ 100 0.50
(Courtesy of O. Hardin and P. Drnevich, “Shear Modulus and
Damping in Soils: Design Equations and Curves,” Journal Soil
Mechanics and Foundations Division, Vol 98, No. SM7, 1972, pp 667-
692. Reprinted by permission of American Society of Civil Engineers,
New York.)
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Table 12-5 Values of Constant K2 Used with Equation (12-24) to Estimate
Cyclic Shear Modulus at Low Strains for Sands
e K2 Dr (%)
0.4 70 90
0.5 60 75
0.6 51 60
0.7 45 45
0.8 39 40
0.9 33 30
(Courtesy of H.B. Seed and I.meters. Idriss, “Simplified Procedures
for Evaluating Liquefaction Potential” Journal Soil Mechanics and
Foundations Division, Vol 97, NoSM(, 1971, pp1249-1273. Reprinted
by permission of American Society of Civil Engineers, New York.)
12-1.5.6 Modulus and Damping at High Strain Levels. The effect of increasingly
higher strain levels is to reduce the modulus (Figure 12-10) and increase the damping
of the soil (Figure 12-11). Shear modulus and damping values at high strains are used
mainly in computer programs for analyzing the seismic response of soil under
earthquake loading conditions. The various empirical relations for modulus and
damping pertain to sands and soft, normally consolidated clays at low-to-medium
effective confining pressures, in the range of about 30 meters (100 feet) or overburden.
Stiff over-consolidated clays and all soils at high effective confining pressure exhibit
lower values of damping and higher values of modulus, especially at high strain levels.
As a maximum, the modulus and damping values for stiff or strong soils at very high
effective confining pressures correspond to values pertaining to crystalline or shale-type
rock.
12-1.6 Settlement and Liquefaction.
12-1.6.1 Settlement. Repeated shearing strains of cohesionless soils cause
particle rearrangements. When the particles move into a more compact position,
settlement occurs. The amount of settlement depends on the initial density of the soil,
the thickness of the stratum, and the intensity and number of repetitions of the shearing
strains. Generally, cohesionless soils with relative densities (Dr) greater than about 75
percent should not develop settlements. However, under 108
or 107
repetitions of
dynamic loading, even dense sands may develop settlements amounting to 1 to 2
percent of the layer thickness. To minimize settlements that might occur under
sustained dynamic loadings, the soil beneath and around the foundation may be pre-
compacted during the construction process by vibroflotation, multiple blasting, or
vibrating rollers acting at the surface. The idea is to subject the soil to a more severe
dynamic loading condition during construction than it will sustain throughout the design
operation.
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12-1.6.2 Liquefaction of Sands. The shearing strength of saturated cohesionless
soils depends upon the effective stress acting between particles. When external forces
cause the pore volume of a cohesionless soil to reduce the amount V, pore water
pressures are increased during the time required to drain a volume V of water from the
soil element. Consequently, pore pressure increases depend upon the time rate of
change in pore volume and the drainage conditions (permeability and available
drainage paths). When conditions permit the pore pressure, u, to build up to a value
equal to the total stress, on, on the failure plane, the shear strength is reduced to near
zero and the mixture of soil grains and water behaves as a liquid. This condition is true
liquefaction, in which the soil has little or no shearing strength and will flow as a liquid.
Liquefaction or flow failure of sands involves a substantial loss of shearing strength for a
sufficient length of time that large deformations of soil masses occur by flow as a heavy
liquid.
12-1.6.3 Liquefaction Due to Seismic Activity. Soil deposits that have a history
of serious liquefaction problems during earthquakes include alluvial sand, Aeolian sands
and silts, beach sands, reclaimed land, and hydraulic fills. During initial field
investigations, observations that suggest possible liquefaction problems in seismic
areas include low penetration resistance; artesian heads or excess pore pressures;
persistent inability to retain granular soils in sampling tubes; and any clean, fine, uniform
sand below the groundwater table. The liquefaction potential of such soils for structures
in seismic areas should be addressed unless they meet one of the criteria in Table 12-6.
In the event that none of the criteria is met and a more favorable site cannot be located,
the material in question should be removed, remedial treatment applied, or a detailed
study and analysis should be conducted to determine if liquefaction will occur.
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Figure 12-10 Variation of Shear Modulus with Cyclic Strain Amplitude; Gmax = G at
ε = 1 To 3 10-4
Percent; Scatter in Data up to About ± 0.1 on Vertical Scale
Figure 12-11 Variation of Viscous Damping with Cyclic Strain Amplitude; Data
Scatter up to About ± 50 of Average Damping Values Shown for Any Strain
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Table 12-6 Criteria for Excluding Need for Detailed Liquefaction Analyses
1. CL, CH, SC or GC Soils
2. GW or GP soils or materials consisting of cobbles, boulders, uniform rock
fill, which have a free-draining boundaries that are large enough to
preclude the development of excess pore properties
3. SP, SW or SM soils that have an average density equal to or greater than
85 percent, provided that the minimum relative density is not less than 80
percent
4. ML or SM soils in which the dry density is equal to or greater than 95
percent of the modified Proctor (ASTM D 1557) density
5. Soils of pre-Holocene age, with natural over consolidation ratio equall to or
greater than 16 and with relative density greater than 70 percent
6. Soils located above the highest potential groundwater table
7. Sands in which the N value is greater than three times the depth in feet, or
greater than 75; provided that 75 percent of the values meet this criterion,
the minimum N value is not less than one times the depth in feet, that there
are no consistent patterns of low values in definable zones or layers, and
that the maximum particle size is not greater than one inch. Large gravel
particles may affect N values so that the results of the SPT are not reliable
8. Soils in which the shear wave velocity is equal to or greater than 2000 fps.
Geophysical survey data and site geology should be reviewed in detail to
verify that the possibility of included zones of low velocity is precluded
9. Soils that, in undrained cycle triaxial tests, under isotropically consolidated,
stress controlled conditions, and with cyclic stress ratios equal to or greater
than 0.45, reach 50 or more with peak-to-peak strains not greater than 5
percent; provided that methods of specimem preparation and testing
conform to specified guidelines
Note: The criteria given above do not include a provision for exclusion of soils on
the basis of grain size distribution, and, in general, grain size distribution
alone cannot be used to conclude that soils will not liquefy. Under adverse
conditions non-plastic soils with a very wide range grain sizes may be
subject to liquefaction.
12-1.7 Seismic Effects on Foundations. Ground motions from earthquakes
cause motions of foundations by introducing forces at the foundation-soil contact
zone. Methods for estimating ground motions and their effects on the design of
foundation elements are discussed in UFC 3-220-10N.
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CHAPTER 13
PILE DRIVING EQUIPMENT
13-1 INTRODUCTION
13-1.1 Purpose. The criteria presented in this UFC are to be used by the engineer
and the construction representative to develop methods and details for driving and
installing pile foundations. The data referenced can aid the engineer in driving, testing
and evaluating the capacity and condition of the piling before, during and after
installation.
13-1.2 Scope. Apply the Geotechnical criteria to all projects for the military services.
The descriptions of pile driving and installation equipment including the weight, stroke,
capacity of hammer, ram weight, helmet, swinging and fixed leads, cushions, cushion
blocks and other hammer criteria and physical properties are presented in the
referenced material.
13-1.3 References.
• Pile Buck, Inc.
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CHAPTER 14
GROUTING METHODS AND EQUIPMENT
14-1 INTRODUCTION
14-1.1 Purpose. The criteria presented in this UFC are to be used by the engineer
and the construction representative to develop methods and details for different types of
grouting to be used in underground construction. The data referenced can aid the
engineer in selecting methods, equipment and type of grouting to obtain the desired
results.
14-1.2 Scope. Apply the Geotechnical criteria to all projects for the military services.
The types of grout and equipment, where to grout and how to grout, and the physical
properties of the grouts are covered in the referenced materials. New methods and
equipment are being developed everyday; therefore, it is imperative to use the
reference often to say abreast of the current knowledge and methods of grouting and
equipment.
14-1.3 Reference.
• See Grouting Publications, ASCE in Appendix A.
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APPENDIX A
REFERENCES
GOVERNMENT PUBLICATIONS:
1. Department of Defense
Unified Facilities Criteria
http://dod.wbdg.org
UFC 3-220-10N, Soil Mechanics
UFC 3-130-01 Arctic and Subarctic
Construction - General Provisions
UFC 3-130-02, Arctic and Subarctic
Construction - Site Selection and
Development
Construction - Runway and Road Design
Construction - Foundations and Structures
Construction - Utilities
Construction - Calculation Methods for
Determination of Depth of Freeze and
Thaw in Soils
UFC 3-130-07, Arctic and Subartic
Construction - Buildings
UFC 3-220-05, Dewatering And
Groundwater Control
NON-GOVERNMENT PUBLICATIONS:
1. Transportation Research Board
Lockbox 289
Washington, D.C. 20055
Or FAX 202-334-2519
2. Virginia Tech
NCHRP VOL. 343, Engineering Manual for
Shallow Foundations, Driven Piles, Drilled
Shafts, Retaining Walls, and Abbutments,
R.L. Allen, J.M. Duncan, R.T. Sancio,
Virginia Tech, Dec 1991
Engineering Manual for Settlement
A-1

UFC 3-220-01N
15 AUGUST 2005
Blacksburg, Virginia 24061
http://cgpr.ce.vt.edu
3. American Society of Civil Engineers
American Society of Civil Engineers
1801 Alexander Bell Drive
Reston, VA 20191
Tel: 800-548-2723
http://www.asce.org
Studies, J.M. Duncan, A.L. Buchignani,
1987
Engineering Manual Sheet Pile Walls, R.L.
Allen, J.M. Duncan, R.T. Sancio, 1987
Engineering Manual for Slope Stability
Studies, J.M. Duncan, A.L. Buchignani,
Marios De Wet
Shear Strength Correlation for
Geotechnical Engineering, J.M. Duncan,
R.C. Horz, T.L. Yang, 1989,
Retaining and Flood Walls, Technical
Engineering and Design Guides as
Adapted from the U.S. Army Corps of
Engineers, No. 4
Soil Sampling, Technical Engineering and
Design Guides as Adapted from the U.S.
Army Corps of Engineers, No. 30, ,
Settlement Analysis, Technical
Engineers, No. 9
Design of Shallow Foundations, Samuel E.
French
Bearing Capacity of Soils, Technical
Engineers, No. 7
Design of Pile Foundations, Technical
Engineers, No. 1
Design of Sheet Pile Walls, Technical
A-2

UFC 3-220-01N
15 AUGUST 2005
Engineers, No. 15
Chemical Grouting, Technical Engineering
and Design Guides as Adapted from the
U.S. Army Corps of Engineers, No. 24
Geophysical Exploration for Engineering
and Environmental Investigations,
Technical Engineering and Design Guides
as Adapted from the U.S. Army Corps of
Engineers, No. 23
20-96, Standard Guidelines for the Design
and Installation of Pile Foundations
EXPANSIVE SOILS PUBICATIONS
Expansive Soils and the Geomembrane
Remedy
Impact of Climatic Variation on Design
Parameters for Slab on Ground
Foundations in Expansive Soils
Mineralogy-Swelling Potential
Relationships for Expansive Shales
Prediction of Heave Using "Effective"
Stress
Suction-Swelling Relations
Using Soil Diffusion to Design Raft
Foundation on Expansive Soils
Evaluation Protocol for Repair of
Residences Damaged by Expansive Soils
Suction Compression Index Based on
CLOD Test Results
Using Soil Suction to Estimate Differential
Soil Shrink or Heave
Piled Rafts in Swelling or Consolidating
Soils
Irrigation, Drainage, and Landscaping for
Expansive Soil
Limitations of Residential Structures on
Expansive Soils
Treating Expansive Soils
Assessment of Expansive Soils in the
United States
Characterization of Expansive Soils Using
Soil Suction Data
A Foundation Code for Expansive Soil
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UFC 3-220-01N
15 AUGUST 2005
Conditions
A Model for Slab Foundations on
Expansive Soils
Pile Foundations in Swelling Soils
Proceedings of the Fourth International
Conference on Expansive Soils
The Structural Analysis of Footings on
Expansive Soil
Review of Expansive Soils
GROUTING PUBLICATIONS
Advances in Grouting and Ground
Modification
An Alternate Compaction Grouting
Technique
An Approach to the Design of Limited
Mobility Displacement (LMD) Grouting
Compensation Grouting: Concept, Theory
and Practice
A Critical Look at Use of "Rules of Thumb"
for Selection of Grout Injection Pressures
Design Verification into the Grouting Pgm
Effects of Grout Composition, Depth and
Injection Rate on Compaction Grouting
Effects of Jet Grouting on Adjacent Ground
and Structures
Equipment for Cement Grouting: An
Overview
Geotechnical Investigations for Grouting in
Soil
Prediction and Validation of Compaction
Grout Effectiveness
Verification of Jet Grouting for Structure
Rehabilitation
Jet Grouting in Cohesive Soils
Abutment Stabilization with Jet Grouting
Jet Grouting: New Directions
Chemical Grouting
Compaction Grouting: From Practice to
Theory
"Compaction Grouting" State of the
Practice 1997
Grouting: Compaction, Remediation and
Testing
Grouting in a Karst Environment
Grouting to Great Depths
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UFC 3-220-01N
15 AUGUST 2005
4. Deep Foundations Institute
Deep Foundations Institute
326 Lafayette Avenue
Hawthorne, NJ 07506
Tel: 973-423-4030
FAX: 973-423-4031
Email: dfihq@dfi.org
http://www.dfi.org/
5. ADSC: THE INTERNATIONAL
ASSOCIATION OF FOUNDATION
DRILLIING
P.O. Box 550399
Dallas, Texas 75355-0339
Tel: 214-343-2091
FAX: 214-343-2384
Email: adsc@adsc-iafd.com
http://www.adsc-iafd.com/
6. Pile Buck®
, Inc.
P.O Box 64-3929
Vero Beach, Florida 32964
Tel: (772) 231-5200
FAX: (772) 231-8400
Influence of Fines Content on the Behavior
of Compaction Grout
Limited Mobility Displacement Grouting:
When "Compaction Grout" is Not
Compaction Grout
Monitoring Systems for Control of
Compensation Grouting
Auger CIP Piles Manual
Inspectors Guide to Augered CIP Piles
Drilled Shaft Inspector’s Manual
Lexicon of Foundation Terms in Five
Languages
Driven Foundation Piling (Catalog 1998)
Dynamic Monitoring and Analysis
Interpretation & Analysis fo the Static
Loading Test
Guidelines for Static Design
Testing of Pile Driving Cushion Material
Soil Nailing Design & Applications
Inspectors Manual for Pile Foundations
Drilled Shafts
Drilled Shafts - Axial Loads
Drilled Shafts - Clay
Drilled Shafts – Concrete
Drilled Shafts - Design
Drilled Shafts – Design, General
Drilled Shafts – General
Drilled Shafts – Non-Destructive Testing
Drilled Shafts – Rock
Drilled Shafts - Sand
Drilled Shafts – Shale, Slurry
Drilled Shafts – Slurry
Drilled Shafts – Soils
Drilled Shafts – Specifications
Drilled Shafts – Testing
Drilled Shafts – Testing, Uplift
Drilled Shafts – Uplift
Earth Retention
Soil Mechanics
Foundations
Earth Support Systems and Retaining
Structures
Mooring Systems
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UFC 3-220-01N
15 AUGUST 2005
http://www.geotechnicaldirectory.com/
A-7
Ill., 1975
12. Clough, G.W. and Davidson, R.R.
13. Terzaghi, K.
14. Petersen E.V.
15. Goldberg, D.T., Jaworksi, W.E. and
Gordon, M.D.
16. Bherrum L., Clausen, J.F. and
Duncan, J.M.
17. Lambe, T.W.
18. Peck, R.B.
19. Caterpillar Tractor Company
listings, meetings, contractors and
professional contacts.
Effects of Constuction on Geotechnical
Engineering, Specilty Session No. 3,
Relationship Between Design and
Construction in Soil Engineering, Ninth
International Conference on Soil
Mechanics and Foundation Engineering,
Tokyo, 1977.
Stability of Steep Slopes on Hard
Unweathered Rock, Norwegian
Geotechnical Institute, Publications No. 50,
1963
Cave-In, Roads and Engineering
Construction, November 1963, December
1963, and January 1964.
Lateral Support Systems and
Underpinning, Vol. II, Design
Fundamentals, Vol. III, Construction
Methods, Federal Highway Administration,
Report Nos. FHWA-RD-75-129, 130, 1976.
Stability of Flexible Structures, General
Report, Proceedings, Fifth-International
European Conference on Soil Mechanics
and Foundation Engineering, Vol. 11, 1977
Braced Excavation, 1970 Specialty
Conference, Lateral Stresses in the
Ground an Design of Earth Retaining
Structures, June 22-24, Cornell University,
ASE, 1971
Deep Excavation and Tunneling in Soft
Ground, Proceedings, Seventh
International Conference on Soil
Mechanics and Foundation Engineering,
State-of-the-Art Vol. 1, 1969
Handbook of Ripping, Fifth Edition, Peoria,

UFC 3-220-01N
15 AUGUST 2005
A-8
20. Franklin, J.A., Broch, E and Walton,
G.
21. Broch, E. and Franklin, J.A.
22. U.S. Department of Interior, Bureau Of
Mines, 1971
23. Hendron, A.J.
Logging the Mechanical Character of
Rock, Tranactions, Institution of Mining
and Metallurgy, January 1971.
The Point-Load Strength Test,
International Journal Rock Mechanics and
Mining Science, Vol. 9, 1972.
Blasting Vibrations and Their Effect on
Structures
Engineering of Rock Blasting on Civil
Projects, Rock Excavation Seminar
Lectures, ASCE, New York, 1976

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