Chapter 3 soil compaction and field density

Geotechnical Engineering 1
(SOIL MECHANICS)

Chapter 2: Soil Compaction and Field
Density
1. Definition and compaction fundamentals
2. Laboratory Tests
3. Field Density Tests
4. Compaction equipment
5. Compaction specification and field control
and measurement
TOPIC OUTLINE

Intended Learning Outcomes
• Understood and explained the principles of soil compaction
• Generated the soil compaction curve and calculated the
maximum dry density and optimum moisture content
• Differentiated the properties of the soil on the wet and dry side of
the compaction curve
• Discussed the different field density test
• Calculated the relative degree of compaction
• Identified the different compaction equipment
• Discussed the compaction specification and field control and
measurements

Compaction
Courtesy of U.S. WICK DRAIN, INC.

What is compaction?
A simple ground improvement technique, where the soil
is densified through external compactive effort.
+ water =
Compactive
effort

Compaction
· The process of bringing the soil particles closer to a dense
state by mechanical means. The voids are reduced by
expulsion of air and the soil particles are packed together,
thereby increasing its unit weight.
· There is no substantial change in the volume of water in soil
during compaction.
· Compaction is done to improve the Engineering properties of
soil such as increase of shear, increase the bearing strength,
reduce the compressibility of soil, change the soil properties
like shrinkage, frost susceptibility and permeability of soils.

Compaction and Objectives
Compaction
•Many types of earth construction, such as dams, retaining walls,
highways, and airport, require man-placed soil, or fill. To compact a soil,
that is, to place it in a dense state.
•The dense state is achieved through the reduction of the air voids in the
soil, with little or no reduction in the water content. This process must
not be confused with consolidation, in which water is squeezed out under
the action of a continuous static load.
Objectives:
(1) Decrease future settlements
(2) Increase shear strength
(3) Decrease permeability (From Lambe, 1991; Head, 1992)

• Increased bearing capacity for foundation support.
• Reduce compressibility and smaller settlement of buildings
and lesser deformation of earth structures.
• Improve stability and lower damage due to frost action.
• Heavy/highway vs. building foundation compaction
operations.
• To reduce the degree of shrinkage and formation of cracks
on drying.
Compaction and Objectives

General Compaction Methods
Coarse-grained soils Fine-grained soils
•Hand-operated vibration plates
•Motorized vibratory rollers
•Rubber-tired equipment
•Free-falling weight; dynamic
compaction (low frequency
vibration, 4~10 Hz)
•Falling weight and hammers
•Kneading compactors
•Static loading and press
•Hand-operated tampers
•Sheepsfoot rollers
•Rubber-tired rollers
Laboratory
Field
Vibration
•Vibrating hammer (BS)
(Holtz and Kovacs, 1981; Head, 1992)
Kneading

Theory of Compaction
(Laboratory Test)

Laboratory Compaction
Origin
The fundamentals of compaction of fine-grained soils are relatively new.
R.R. Proctor in the early 1930’s was building dams for the old Bureau of
Waterworks and Supply in Los Angeles, and he developed the principles
of compaction in a series of articles in Engineering News-Record. In his
honor, the standard laboratory compaction test which he developed is
commonly called the proctor test.
Purpose
The purpose of a laboratory compaction test is to determine the proper
amount of mixing water to use when compacting the soil in the field and
the resulting degree of denseness which can be expected from compaction
at this optimum water
Impact compaction
The proctor test is an impact compaction. A hammer is dropped several
times on a soil sample in a mold. The mass of the hammer, height of drop,
number of drops, number of layers of soil, and the volume of the mold are
specified.

Various Types
Various types of compaction test
1
2
3
1: your test 2: Standard Proctor test 3: Modified Proctor test

Test Equipment
Standard Proctor test equipment
Das, 1998

Comparison-
Standard and Modified Proctor Compaction Test
Summary of Standard Proctor Compaction Test
Specifications (ASTM D-698, AASHTO)
Das, 1998

Comparison-
Standard and Modified Proctor Compaction Test (Cont.)
Summary of Modified Proctor Compaction Test
Specifications (ASTM D-698, AASHTO)
Das, 1998

Comparison-Summary
Standard Proctor Test
12 in height of drop
5.5 lb hammer
25 blows/layer
3 layers
Mold size: 1/30 ft3
Energy 12,375 ft·lb/ft3
Modified Proctor Test
18 in height of drop
10 lb hammer
25 blows/layer
5 layers
Mold size: 1/30 ft3
Energy 56,250 ft·lb/ft3
Higher compacting energy

Comparison-Why?
• In the early days of compaction, because construction equipment was
small and gave relatively low compaction densities, a laboratory
method that used a small amount of compacting energy was required.
As construction equipment and procedures were developed which gave
higher densities, it became necessary to increase the amount of
compacting energy in the laboratory test.
• The modified test was developed during World War II by the U.S.
Army Corps of Engineering to better represent the compaction required
for airfield to support heavy aircraft. The point is that increasing the
compactive effort tends to increase the maximum dry density, as
expected, but also decrease the optimum water content.
(Holtz and Kovacs, 1981; Lambe, 1991)

Variables of Compaction
Proctor established that compaction is a function of four variables:
(1)Dry density (d) or dry unit weight d.
(2)Water content w
(3)Compactive effort (energy E)
(4)Soil type (gradation, presence of clay minerals, etc.)
)
ft
/
lb
ft
375
,
12
(
m
/
kJ
7
.
592
m
10
944
.
0
)
layer
/
blows
25
)(
layers
3
)(
m
3048
.
0
)(
s
/
m
81
.
9
(
kg
495
.
2
E
3
3
3
3
2





Volume of mold
Number of
blows per
layer
Number of
layers
Weight of
hammer
Height of
drop of
hammer
  
E =
For standard
Proctor test

Procedures and Results
Procedures
(1) Several samples of the same soil, but at different water contents, are
compacted according to the compaction test specifications.
(2) The total or wet density and the actual water content of each
compacted sample are measured.
(3) Plot the dry densities d versus water contents w for each compacted
sample. The curve is called as a compaction curve.
w
1
,
V
M
d
t
t





 Derive d from the known 
and w
The first four blows
The successive blows

*Volume of
standard mold
is 943.9 cm3
**Dry density
=
density/(1+w)
Procedures and Result

Procedures and Results (Cont.)
Results
Zero air
void
Water content w (%)
Dry
density

d
(Mg/m
3
)
Dry
density

d
(lb/ft
3
)
Line of
optimums
Modified
Proctor
Standard
Proctor
Peak point
Line of optimum
Zero air void
Holtz and Kovacs, 1981
d max
wopt

The peak point of the compaction curve
The peak point of the compaction curve is the point with the maximum
dry density d max. Corresponding to the maximum dry density d max is a
water content known as the optimum water content wopt (also known as
the optimum moisture content, OMC). Note that the maximum dry density
is only a maximum for a specific compactive effort and method of
compaction. This does not necessarily reflect the maximum dry density
that can be obtained in the field.
Zero air voids curve
The curve represents the fully saturated condition (S = 100 %). (It cannot
be reached by compaction)
Line of optimums
A line drawn through the peak points of several compaction curves at
different compactive efforts for the same soil will be almost parallel to a
100 % S curve, it is called the line of optimums

s
w
s
w
w
d
G
S
w
S
S
w
S









The Equation for the
curves with different
degree of saturation is :
s
s
d
wG
Se
e
1





You can derive the equation
by yourself
Hint:

w
d
(wopt, d max)
Procedures and Results-Explanation
Below wopt (dry side of optimum):
As the water content increases, the particles
develop larger and larger water films around
them, which tend to “lubricate” the particles
and make them easier to be moved about and
reoriented into a denser configuration.
At wopt:
The density is at the maximum, and it does
not increase any further.
Above wopt (wet side of optimum):
Water starts to replace soil particles in the
mold, and since w << s the dry density
starts to decrease.
Lubrication or
loss of suction??

Compaction Curve
Water content
Dry
density
(
d
)
optimum
water content
d, max
Soil grains densely packed
- good strength and stiffness
- low permeability

Procedures and Results-Notes
• Each data point on the curve represents a single
compaction test, and usually four or five individual
compaction tests are required to completely determine the
compaction curve.
• At least two specimens wet and two specimens dry of
optimum, and water contents varying by about 2%.
• Optimum water content is typically slightly less than the
plastic limit (ASTM suggestion).
• Typical values of maximum dry density are around 1.6 to
2.0 Mg/m3 with the maximum range from about 1.3 to 2.4
Mg/m3. Typical optimum water contents are between 10%
and 20%, with an outside maximum range of about 5% to
40%.

Factors affecting Compaction
Five factors affecting compaction
1. Physical & chemical properties
2. Moisture content
3. Method of compaction
4. Amount of compactive effort
5. Thickness of layer or “lift” being
compacted

Factors affecting compaction: Effects of Soil Types
The soil type-that is, grain-size distribution, shape of the soil grains,
specific gravity of soil solids, and amount and type of clay minerals
present.
Holtz and Kovacs, 1981; Das, 1998

Factors affecting compaction: Effects of Compaction
Effort
As the compaction effort
increased, the max dry unit
weight of compaction is also
increased and the optimum
moisture content is decreased
to some extent.
The degree of compaction is
not directly proportional to the
compaction effort.

Water Content
Dry Density
Effect of Energy on Soil Compaction
Higher
Energy
Z
A
V
Increasing compaction energy Lower MC and higher dry density
In the field
increasing compaction energy =
increasing number of passes or
reducing lift depth
In the lab
increasing compaction energy
= increasing number of blows

Field and Laboratory Compaction
•It is difficult to choose a
l a b o r a t o r y t e s t t h a t
reproduces a given field
compaction procedure.
•T h e l a b o r a t o r y c u r v e s
generally yield a somewhat
lower optimum water content
than the actual field optimum.
•T h e m a j o r i t y o f f i e l d
compaction is controlled by
the dynamic laboratory tests.
Curve 1, 2,3,4: laboratory compaction
Curve 5, 6: Field compaction
(From Lambe and Whitman, 1979)

Properties and Structure of Compacted
Fine-grained Soils

Structure of Compacted Clays
•For a given compactive
effort and dry density, the
s o i l t e n d s t o b e m o r e
flocculated (random) for
compaction on the dry side
as compared on the wet side.
•For a given molding water
content, increasing the
compactive effort tends to
disperse (parallel, oriented)
the soil, especially on the
dry side.
Lambe and Whitman, 1979

Engineering Properties-Permeability
• Increasing the water content
r e s u l t s i n a d e c r e a s e i n
permeability on the dry side of
the optimum moisture content
a n d a s l i g h t i n c r e a s e i n
permeability on the wet side of
optimum.
• Increasing the compactive effort
reduces the permeability since it
both increases the dry density,
thereby reducing the voids
available for flow, and increases
the orientation of particles.
From Lambe and Whitman, 1979;

Engineering Properties-Compressibility
At low stresses the sample compacted on the wet side is
more compressible than the one compacted on the dry side.

Engineering Properties-Compressibility
At the high applied stresses the sample compacted on the dry side
is more compressible than the sample compacted on the wet side.

Engineering Properties-Swelling
• Swelling of compacted clays is greater for those compacted
dry of optimum. They have a relatively greater deficiency
of water and therefore have a greater tendency to adsorb
water and thus swell more.
w
d
(wopt, d max)
Higher
swelling
potential
From Holtz and Kovacs, 1981
Higher
shrinkage
potential

Engineering Properties-Strength
Samples (Kaolinite)
compacted dry of
optimum tend to be
m o r e r i g i d a n d
s t r o n g e r t h a n
samples compacted
wet of optimum
From Lambe and
Whitman, 1979

Engineering Properties-Strength (Cont.)
The CBR (California bearing ratio)
CBR= the ratio between resistance required
to penetrate a 3-in2 piston into the
compacted specimen and resistance
required to penetrate the same depth into a
standard sample of crushed stone.
A greater compactive effort produces a
greater CBR for the dry of optimum.
However, the CBR is actually less for
the wet of optimum for the higher
compaction energies (overcompaction).

Engineering Properties-Summary
Dry side Wet side
Permeability
Compressibility
Swelling
Strength
Structure More random More oriented
(parallel)
More permeable
More compressible in
high pressure range
More compressible in
low pressure range
Swell more,
higher water
deficiency
Higher
Please see Table 5-1
*Shrink more

Engineering Properties-Summary (Cont.)
Please find this
table in the
textbook of
Holtz and
Kovacs

Engineering Properties-Notes
• Engineers must consider not only the behavior of the soil as compacted
but the behavior of the soil in the completed structure, especially at the
time when the stability or deformation of the structure is most critical.
• For example, consider an element of compacted soil in a dam core. As the
height of the dam increases, the total stresses on the soil element increase.
When the dam is performing its intended function of retaining water, the
percent saturation of the compacted soil element is increased by the
permeating water. Thus the engineer designing the earth dam must
consider not only the strength and compressibility of the soil element as
compacted, but also its properties after is has been subjected to increased
total stresses and saturated by permeating water.
Lambe and Whitman, 1979

Field Compaction Equipment
and Procedures

Field Soil Compaction
Because of the differences between lab and field compaction
methods, the maximum dry density in the field may reach 90% to
95%.
Moisture
Content
Dry Density
d max
(OMC)
95% d max

50
Soil Compaction in the Field:
1- Rammers
2- Vibratory Plates
3- Smooth Rollers
4- Rubber-Tire
5- Sheep foot Roller
6- Dynamic Compaction

Equipment
Smooth-wheel roller (drum) • 100% coverage under the wheel
• Contact pressure up to 380 kPa
• Can be used on all soil types
except for rocky soils.
• Compactive effort: static weight
• The most common use of large
smooth wheel rollers is for proof-
rolling subgrades and compacting
asphalt pavement.

Equipment (Cont.)
Pneumatic (or rubber-tired) roller • 80% coverage under the wheel
• Contact pressure up to 700 kPa
• Can be used for both granular and
fine-grained soils.
and kneading.
• Can be used for highway fills or
earth dam construction.

Equipment (Cont.)
Sheepsfoot rollers • Has many round or rectangular
shaped protrusions or “feet”
attached to a steel drum
• 8% ~ 12 % coverage
• Contact pressure is from 1400 to
7000 kPa
• It is best suited for clayed soils.
and kneading.

Equipment (Cont.)
Tamping foot roller • About 40% coverage
8400 kPa
• It is best for compacting fine-
grained soils (silt and clay).
and kneading.

Equipment (Cont.)
Mesh (or grid pattern) roller • 50% coverage
6200 kPa
• It is ideally suited for compacting
rocky soils, gravels, and sands.
With high towing speed, the
material is vibrated, crushed, and
impacted.
and vibration.

Equipment (Cont.)
Vibrating drum on smooth-wheel
roller
• Vertical vibrator attached to
smooth wheel rollers.
• The best explanation of why roller
vibration causes densification of
granular soils is that particle
rearrangement occurs due to cyclic
deformation of the soil produced
by the oscillations of the roller.
and vibration.
• Suitable for granular soils

Equipment-Summary

Field Compaction
Control and Specifications

Control Parameters
• Dry density and water content correlate well with the
engineering properties, and thus they are convenient
construction control parameters.
• Since the objective of compaction is to stabilize soils and
improve their engineering behavior, it is important to keep
in mind the desired engineering properties of the fill, not
just its dry density and water content. This point is often
lost in the earthwork construction control.

Design-Construct Procedures
• Laboratory tests are conducted on samples of the proposed
borrow materials to define the properties required for
design.
• After the earth structure is designed, the compaction
specifications are written. Field compaction control tests
are specified, and the results of these become the standard
for controlling the project.

Specifications
(1) End-product specifications
This specification is used for most highways and building
foundation, as long as the contractor is able to obtain the
specified relative compaction , how he obtains it doesn’t
matter, nor does the equipment he uses.
Care the results only !
(2) Method specifications
The type and weight of roller, the number of passes of that
roller, as well as the lift thickness are specified. A maximum
allowable size of material may also be specified.
It is typically used for large compaction project.

Field Compaction
• Field Compaction depends on:
· Weight of roller
· No of passes of roller
• Relative compaction is given in specification for
field compaction, which is the ratio of field dry
density to the maximum lab density, whereas the
Lab dry density is determined by Standard or
Modified AASHTO tests.
• For example 95% compaction of modified
AASHTO dry density

Relative Compaction (R.C.)
%
100
.
C
.
R
laboratory
max
d
filed
d






r
D
2
.
0
80
.
C
.
R 

Relative compaction or percent compaction
Correlation between relative compaction
(R.C.) and the relative density Dr
It is a statistical result
b a s e d o n 4 7 s o i l
samples.
As Dr = 0, R.C. is 80
Typical required R.C. = 90% ~ 95%

Determine the Water Content (in Field)
Control
(1) Relative compaction
(2) Water content (dry side
or wet side)
N o t e : t h e e n g i n e e r i n g
properties may be different
between the c ompa c te d
sample at the dry side and at
the wet side.
100% saturation
Water content w %
wopt
Dry
density,

d
d max
Line of
optimums
90% R.C.
 

a c
Increase
compaction
energy
b

Determine the Relative Compaction in the Field
Where and When
• First, the test site is selected. It should be representative or typical of the
compacted lift and borrow material. Typical specifications call for a new
field test for every 1000 to 3000 m2 or so, or when the borrow material
changes significantly. It is also advisable to make the field test at least
one or maybe two compacted lifts below the already compacted ground
surface, especially when sheepsfoot rollers are used or in granular soils.
Method
• Field control tests, measuring the dry density and water content in the
field can either be destructive or nondestructive.

Typical Compaction Requirements

Destructive
Methods
Methods
(a) Sand cone
(b) Balloon
(c) Oil (or water) method
Calculations
•Know Ms and Vt
•Get d field and w (water content)
•Compare d field with d max-lab
and calculate relative compaction
R.C.
(a)
(b)
(c)

In-Place Test: Sand-cone method

Example
During construction of a soil embankment, a sand-cone
in-place unit weight test was performed in the field.
· Weight of sand used to fill test hole and funnel of sand-
cone device = 867g
· Weigh of sand to fill funnel = 319g
· Unit weigh of sand = 98.0 lb/ft3
· Weigh of wet soil from the test hole = 747g
· Moisture content of soil from test hole = 13.7%

A sand cone holds 851.0 g. The loose density of the
sand is 1.430 g/cm3
Field Test Results:
Total weight of the soil 639.5 g
Dry weight of the soil 547.9 g
Initial weight of the sand-cone apparatus 4527.8g
final weight of the sand-cone apparatus 3223.9g
Sample Problem

Corrected Maximum Dry Density
· compaction test is usually done on materials finer than
4.75 mm
· sample contains coarse grained sized particles
– gravel in a soil composed mainly of fine grains can
be compacted to 90% of their theoretical maximum
density
– assuming gravel RD=2.65
Corrected MDD due to presence of gravel

Calculations:
Mass of the sand used 4527.8g-3223.9g = 1303.9g
Mass in test hole 1303.9g-851.0g = 452.9 g
Volume of test hole 452.9 g = 316.7 cm3
1.430 g/cm3
Field dry density 547.9g/316.7 cm3 = 1.730 g/ cm3
Field water content 639.5-547.9 = 16.7%
547.9
Sample Problem

Laboratory maximum density of a soil is 1900
kg/m3. Specifications require 95% compaction.
In the field, dry density of the soil is found to be
1810kg/m3. A visual check of the soil in the field
indicates that it contains about 20% gravel sizes.
(Scales can be used for a more accurate
determination of the percentage of gravel.)
Check for compaction.
Sample Problem

Corrected maximum dry density is:
0.80 x 1900kg/m3 + 0.20 x (90% x 2.65 x 1000kg/m3
= 1520 kg/m3 + 477kg/m3 = 1997kg/m3
Percent compaction is 1810/1997 = 90.6% and is
not acceptable
Sample Problem

Destructive Methods (Cont.)
Sometimes, the laboratory maximum density may not be
known exactly. It is not uncommon, especially in highway
construction, for a series of laboratory compaction tests to be
conducted on “representative” samples of the borrow
materials for the highway. If the soils at the site are highly
varied, there will be no laboratory results to be compared
with. It is time consuming and expensive to conduct a new
compaction curve. The alternative is to implement a field
check point, or 1 point Proctor test.

Check Point Method
Water content w %
wopt
Dry
density,

d
d max
100% saturation
Line of
optimums
A
B
M
C
X
Y(no)
•1 point Proctor test
•Known compaction
curves A, B, C
•Field check point X
(it should be on the
dry side of optimum)

• The measuring error is mainly from the determination of
the volume of the excavated material.
For example,
• For the sand cone method, the vibration from nearby working
equipment will increase the density of the sand in the hole, which will
gives a larger hole volume and a lower field density.
• If the compacted fill is gravel or contains large gravel particles. Any
kind of unevenness in the walls of the hole causes a significant error in
the balloon method.
• If the soil is coarse sand or gravel, none of the liquid methods works
well, unless the hole is very large and a polyethylene sheet is used to
contain the water or oil.
t
s
field
d V
/
M

 

Nondestructive
Methods
Nuclear density meter
(a) Direct transmission
(b) Backscatter
(c) Air gap
(a)
(b)
(c)
Principles
Density
The Gamma radiation is scattered by the soil
particles and the amount of scatter is
proportional to the total density of the material.
The Gamma radiation is typically provided by
the radium or a radioactive isotope of cesium.
Water content
The water content can be determined based on
the neutron scatter by hydrogen atoms. Typical
neutron sources are americium-beryllium
isotopes.

Nondestructive Methods (Cont.)
Calibration
Calibration against compacted materials of known density is
necessary, and for instruments operating on the surface the
presence of an uncontrolled air gap can significantly affect
the measurements.

Chapter 3 soil compaction and field density

More Related Content

What's hot (20)

Similar to Chapter 3 soil compaction and field density (20)

Recently uploaded (20)

Chapter 3 soil compaction and field density