WU_Engineering geology_lecture note_Elias.pdf

Wollo University
College of Natural Sciences
Department of Geology
Engineering Geology (Geol 4112)
By: Elias Assefa (MSc)
1
Wollo University, Ethiopia Elias A.

Course Title: Engineering Geology
Course Code: Geol. 4112
Credit hours: 4 credit or 6 ECTS
Course Category: Core course
Instructors: Elias Assefa (MSc)
eliasassefa29@gmail.com
Cellphone no. +251910110141
2

Course Aim/Rationale
The course is aimed to increase your
knowledge of application of geology in civil
engineering practice.
3

Course Learning Outcomes
Upon successful completion of this course, you will be able to:
 Acquire a basic understanding of the principles of site investigation and able to
conduct geotechnical site investigation
 Acquire a basic understanding to prepare an engineering geological map.
 Acquire a basic understanding of different engineering structures (dam, tunnel,
road, bridge, building and others) and evaluate theirs suitable site and foundation
condition.
 Acquire a basic understanding to identify the suitable potential source of
geological construction material and characterize the geological construction
material for different engineering structures.
 Acquire a basic understanding to access and evaluate different geological hazards
on different engineering structures and recommend their mitigation measures.
4

COURSE OUTLINE
Engineering Site Investigation and Exploration
Hazardous of Earth Processes and Engineering Works
 Subsurface Water and Engineering Works
 Introduction to Dams and dam sites
 Introduction to engineering geology of tunnel working
Engineering Geology of River Engineering and Hydraulic Structures
 Engineering Geology and Shallow Foundation Structures
Geological Construction Material
Engineering geological mapping
5

6

Recommended References
 Ayenew T. (2004), Fundamental of Engineering Geology, teaching book,
department of geology and geophysics, Addis Ababa University.
 Bell F.G. (2007), Engineering Geology, pub Elsevier.
 Blyth F.G.H & Freitas D.H. (2007), A Geology for engineers, pub Elsevier,
Delhi, India.
 Deerman W. R (1991), Engineering geological mapping. Oxford, Pp. 1-23.
 Franklin J.A. and Dusseault M. (1991), Rock Engineering Applications),
McGraw Hill, New York, 431p.
 Garg S.K. (2008), physical and engineering geology, Khanna pub, Delhi, India,
pp. 30- 257.
 Goodman, R.E. (1989) Introduction to Rock Mechanics, 2nd Edition, John
Wiley & sons.
 Hoek E. & Bray J.W. (1991) Rock slope engineering.
7

Chapter one:
Introduction to engineering geology
8

9
General overview and definition of Engineering Geology
What is engineering geology?
Definition:-
a) The science which deals with the physical structure and substance of
the earth, their history, and the processes which act on them.
b) The geological features of a district.
c) The geological features of a planetary body.
• Engineering Geology provide geological and geotechnical
recommendations, analysis and design related to human development
and different types of structures. The engineering geologist’s realm is
essentially about earth-structure interactions or investigating how
earth or earth processes impact human-made structures and human
activities.
• Engineering geologists are involved in processes that modify surface
and sub-surface geology for the built environment.
• They may also be involved in the related disciplines of engineering
geophysics, hydrogeology and mineral exploration.

Functions of Engineering
Geology
10
• Description of the geologic environments pertinent to
the engineering practice.
• Description of earth materials, their distribution and
general physical/chemical characteristics.
• Deduction (investigate) of the history of pertinent
events affecting the earth materials.
• Forecasting of future events and conditions that may
develop.
• Recommendations of ways to handle and treat various
earth processes.

cont’
d
11
In engineering geology; there are three premises:
1. All engineering works are built in or on the ground.
2. The ground will always react to the construction of the
engineering works.
3. The reaction of the ground (engineering behaviour) to
the engineering work must be accommodated (within
allowable limit).

cont’
d
12
Toarrive at the engineering behaviour of the ground, there are
common relations or equations between rock, rock mass and
engineering/structure:
1. Material properties + mass fabric = Mass property
2. Mass property + environment = Engineering geological
condition
3. Engineering geological condition+ changes produced by
engineering work = Engineering Behaviour of the Ground.
Let’s see all the variables in the equations above and their
significance:
• Material: rock, soil, and fluids and/or gas
• Material property: density, shear strength, deformability, etc.

cont’
d
13
• Mass fabric: beds, dykes, veins, joints, faults, etc.
• Mass: ground mass, volume of ground which will be influenced
by or will influence the engineering work.
• Environment: includes
– climate,
– stress condition,
– Natural and man-made hazards and earthquakes, etc.
– Time: immediate after construction, after construction and
through its life time.
In the three equations all the factors leading up to the description
of the engineering geological situation/ condition may be
established by the process of site investigation (chapter two).

CHAPTER I
1
Engineering geological site investigations
14

Engineering Site Investigation and Exploration
 Site investigation (stages, tools, methods)
 Disturbed and undisturbed samples (samples and
samplers)
 Boring and sampling
 Cores sizes and core recovery
15

16

17

18
Site investigation and soil exploration:
 Objectives - planning - reconnaissance - depth and lateral extent of
explorations –
 methods of subsurface exploration - test pits - Auger borings - rotary drilling
 Types of soil samples-split spoon samplers- Standard penetration test-
hand cut samples- boring log - soil profile- geophysical methods.
OBJECTIVES OF SOIL INVESTIGATION
● Determination of
– The nature of the deposits of soil
– The depth and thickness of the various soil strata and their extent in the horizontal
direction
– The location of ground water and fluctuations in GWT
– Engineering properties of the soil and rock strata by conducting laboratory tests
– In-situ properties of soil by performing field tests
● Obtaining soil and rock samples from the various strata

19
Geotechnical investigations are to be carried out by
– engineering geologists,
– geological engineers,
– geotechnical engineers,
– geologists
– civil engineers
 those with education and experience in geotechnical investigations….
Factors influencing the selection of methods of investigation include:
a) Nature of subsurface materials and groundwater conditions.
b) Scope of the investigation, e.g., feasibility study, formulation of plans and
specifications.
c) Size of structure to be built or investigated.

20
d. Purpose of the investigation, e.g., evaluate stability of existing
structure, design a new structure.
e. Complexity of site and structure.
f. Topographic constraints.
g. Difficulty of application.
h. Degree to which method disturbs the samples or surrounding
grounds.
i. Constraints….(Budget, Time, Political constraints)
k. Environment requirements/consequences.

21

22
RECONNAISSANCE
● Inspection of the site and study of the topographical features
● Study of maps and other relevant records.
● Collect details about proposed constructions
● Collect already existing data and then examine for soils and geological
conditions
● Collect details required for economic designs
● Helps in deciding future programme of site investigations, scope of work,
methods of exploration to be adopted, types of samples to be taken and the
laboratory testing and in-situ testing.

PRELIMINARY INVESTIGATIONS
23
● To determine the depth, thickness, extent and composition of each
stratum at the site.
● The depth of bed rock and the ground water table is also
determined.
● Generally in the form of test pits and few borings
● Tests are conducted with cone penetrometers and sounding rods to
obtain information about the strength and compressibility of soils.
● Geophysical methods are used for locating the boundaries of different
strata.

There are two ground characterization model
24

25

26

27

2
Stages in Site Investigation
1. Planning
2. Implementation
3. Interpretation [analysis]
4. Reporting
28

3
29

4
30

31
Stage 1: desk study

5
32

33
Stage 1: walkover survey

6
34

35
Stage 2: shallow geophysical survey

7
36

37
Stage 3: main ground investigation

8
Stages in Site Investigation
1. Desk Study and Walk over Survey
2. Sub‐surface investigation
– In‐situ testing and sampling
– Laboratory testing
3. Report writing
4. Monitoring
Sub‐surface investigation
• to learn the specific geology underneath site.
38

9
39

10
40

11
41

12
42

13
43

14
Borehole
44

15
Post hole auger Helical auger
45

16
46

17
47

18
48

19
Percussion Boring
 Dry boring or water circulated to remove loose soil
 Heavy drilling bit or chisel is dropped while inside the casing to
chop the hard soil.
 Percussion drilling rods may be replaced by cables.
Number of Boring
 There are no hard and fast rules for the number and spacing of the
boreholes.
 The tables give some general guidelines for borehole spacing.
 can be increased or decreased, depending on the subsoil condition.
49

20
Spacing Boring
Approximate Spacing of Boreholes
50

21
Depth of Boring
 When deep excavations are anticipated, the depth of boring should be at, least
1.5 times the width of excavation.
 depth of core boring into the bedrock is about 3m.
 If the bedrock is irregular or weathered, the core borings may have to be
extended to greater depths.
Depth of Boring
51

22
52

Sampling and Sampler in Boreholes
53

23
54

24
55

25
56

26
57

27
58

Soil Sampling
Disturbed vs. Undisturbed
Two types of soil samples can be obtained during sampling:
disturbed and undisturbed.
 The most important engineering properties required for foundation design are
strength, compressibility, and permeability.
These tests require undisturbed samples.
 Disturbed samples can be used for determining other properties such as
Moisture content, Classification & Grain size analysis, Specific Gravity, and
Plasticity Limits.
59

60

61

62

63

64

65

66

67

68

28
69

29
70

30
Sample storage, handling and transportation
71

31
Common Sampling Methods
72

73

32
Laboratory testing
 Advantage: tests can be precise controlled and measurement of tests is
possible.
 Disadvantage: is to bring samples to laboratory without changing (or
disturbing)
Disturbed Samples: Natural soil structure is modified or destroyed during
sampling
 Representative Samples:
Natural water content and mineral constituents of particular soil layer are
preserved
Good for soil identification and water content
Non-representative Samples:
Water content altered and soil layers mixed up
74

Undisturbed Samples:
• Soil structure and the other mineral properties are preserved to an
extent.
• Some disturbance is always there, e.g. due to stress release.
• However it should be minimized in order to have suitable sample for
our analysis.
 It needed to determine
• shear strength parameters in-situ density and water content
• coefficient of permeability consolidation parameters
75

34
In‐situ testing
76

36
IN‐SITU TESTING
 Advantages: soil/rock sample is not disturbed by bringing it to the laboratory and
is being tested in its natural state in the ground.
 Disadvantage: the test cannot be precisely controlled and measured like in the
laboratory.
 Because of these advantages and disadvantages, for most site
In‐situ testing can be grouped into
 Penetration Testing
– SPT, CPT….
 Strength and Compressibility Testing
– Field vane test , Pressuremeter testing , Plate loading tests,
Dilatometer (DMT)…..
 Permeability Testing
– Packer or ‘Lugeon’ test
ASSIGNMENT 1
10%
77

37
PENETRATION TESTING
 Many forms of in situ penetration test are in use worldwide.
 Penetrometers can be divided into two broad groups.
– Dynamic penetrometers (simplest)
– Static penetrometers (more complicated)
The two most common penetration tests, which are used virtually
worldwide, are
– the dynamic SPT, and the static CPT
78

1
Chapter II
Hazardous Earth processes and Engineering works
79

80
HAZARDOUS EARTH PROCESSES AND ENGINEERING WORKS
1. Land‐movements and Flooding
[EXTERNAL FACTORS]
2. Earthquake and Volcanisms
[INTERNAL FACTORS]

81

What is geohazard ?
is a geologic event that has the potential to causing
great loss of life and property damage.
82
Introduction
What is natural hazard?
• Natural events causing both destroy property and cause a
loss of life or property damage

83

84
Definition and concepts
Forecasting, or predicting, the interaction of engineering
works with earth processes is necessary for safety and
reliability.
i. Natural hazard: means the probability of occurrence within
a specified period of time and within a given area of a
potentially damaging phenomena.

85
ii. Vulnerability: means the degree of loss to a given element of set
of elements at risk-resulting from the occurrence of a natural
phenomena of a given magnitude.
 It is expressed on a scale from 0 (no damage) to 1 (total
damage).
iii.Elements at risk: means the population, properties, economic
activities, including public services etc. at risk in a given area.
iv. Specific risk: means the expected degree of loss due to a particular
natural phenomena.

86
Major Types of Geo-hazards
(a) Slope failures are landslides, which can occur in almost any
hilly or mountainous terrain, or offshore
 The potential for failure is identifiable, and therefore forewarning
is possible, but the actual time of occurrence is not
predictable.
 Most slopes can be stabilized, but under some
conditions failure cannot be prevented by reasonable
means.

(b) Ground subsidence, collapse, and expansion usually are the result of
human activities and range from minor to major hazards, although loss of life
is seldom great as a consequence.
87
Their potential for occurrence evaluated on the basis of geologic
conditions, is for the most part readily recognizable and they are
therefore preventable or their consequences are avoidable.
(c) Earthquakes-represent the greatest hazard in terms of potential
destruction and loss of life. They are the most difficult hazard to assess in
terms of their probability of occurrence and magnitude as well as their
vibrational characteristics, which must be known for a seismic
design of structures.
Recognition of the potential on the basis of geologic conditions and
historical events provides the information for a seismic design.

(d) Volcanic activities is the upcoming of materials from the
interior part of the earth.
88
 it can be liquid (lava), solid (pyroclastic materials), and
volatile gases
(e) Floods- have a high frequency of occurrence, and under certain
conditions can be anticipated.
 Protection is best provided by avoiding potential flood areas, which
is not always practical. Prevention is possible under most conditions,
but often at substantial costs.
(f) Health hazards-related to geologic conditions include asbestos,
silica and radon, and the various minerals found in groundwater such as
arsenic and mercury.
Recently, mold has been added to the list of health
hazards. Wollo University, Ethiopia Elias A.

89
2.1. Landslide hazards and its mitigation measure:
Common responsible factors for the occurrence of
landslide, Types of landslides, Engineering problems related
to landslide and Mitigation measure of landslide hazards

2.1. Mass movement/mass wasting
90
2
What is landslide
 A “landslide” can be define as a downward movement of rock or soil,
or both, occurring on the surface of rupture-either rotational slide
(curved), free falling or translational slide (planar) rupture-in which
major parts of the material often moves as a coherent or semi-
coherent mass with little internal deformation under the force of
gravity.
 The term landslide is used in alternative with the mass
movement/mass wasting.
• Mass movement:
– Occur in terrain ranging from vertical cliff to gentle slope
– Velocity range from extremely slow to extremely rapid
– In completely dry to completely wetted states of earth’s material
• Materials include natural rock, soil, artificial fills, or combination
these.

91
o The speed of the movement may range from very slow to rapid.
o The speed of the landslide will make an even more or less
avoidable and therefore, more or less risky.
o It is important to distinguish the different types of landslides to
be able to understand how to deal with each of them.

• CONCEPTS OF SLOPE STABILITY
• Factors that Influence Slope Stability
• GRAVITY
 The main force responsible is gravity
• On a flat surface the force of gravity acts downward
 On a slope, the force of gravity can be resolved into
• perpendicular to the slope and tangential to the slope
92

Slope Stability
93
• Safety Factor: = Resisting/Driving Forces If SF >1, then
safe or stable slope
If SF <1, then unsafe or unstable slope
• Driving and resisting force variables depend on:
– Slip surface – “plane of weakness”
– Type of Earth materials
– Slope angle and topography
– Climate, vegetation, and water
– Shaking

Slopes
94
CONCEPTS OF SLOPE STABILITY
Factors that Influence Slope Stability
THE ROLE OF WATER
 Dry unconsolidated grains will form a pile with a slope angle
determined by the angle of repose. The angle of repose is the
steepest angle at which a pile of unconsolidated grains remains
stable, and is controlled by the frictional contact between the grains.
 In general, for dry materials the angle of repose increases with
increasing grain size, but usually lies between about 30 and 37o.

95
THE ROLE OF WATER
 Slightly wet unconsolidated materials exhibit a very high angle of repose because
surface tension between the water and the solid grains tends to hold the grains in
place.
 When the material becomes saturated with water, the angle of repose is reduced to
very small values and the material tends to flow like a fluid.

96
CONCEPTS OF SLOPE STABILITY
Factors that Influence Slope Stability
THE ROLE OF WATER
 Another aspect of water that affects slope stability is fluid pressure.
 In some cases fluid pressure can build in such a way that water can
support the weight of the overlying rock mass.
 When this occurs, friction is reduced, and thus the shear strength
holding the material on the slope is also reduced, resulting in slope
failure.
 Water fills voids and increase weight which increases driving forces
 Water also exerts pore pressures which decrease effective stress and
therefore strength

97
Types of landslide:

9
COMMON TYPES OF LANDSLIDES
a) Rotational slides move along a
surface of rupture that is curved and
concave
b) Translational slides occurs when the
failure surface is approximately flat or
slightly undulated
98

10
c) Rock Fall:
Free falling of detached bodies of
bedrock (boulders) from a cliff or
steep slope
d) Rock toppling occurs when
one or more rock units rotate
about their base and Collapse.
99

11
e) Lateral spreading
occurs when the soil mass spreads
laterally and this spreading comes with
tensional cracks in the soil mass.
f) Debris Flow:
Down slope movement of
collapsed, unconsolidated material
typically along a stream channel.
100

101
Landslides may also be classified according to their causes.
Deoja et al.,1991 classify landslides into following categories.
1) Rainfall induced landslides
2) Earthquake induced landslides
3) Cloudburst induced landslides – mostly mud flows, debris flows and
flash floods.
4) Landslide dam break
5) Glacial lake outburst flood
6) Freeze and thaw induced rock falls during sunny days in the snow
bound steep rocky mountains.
Causative classification

102
Types of Rock Failure
The possible mode of failures in
rock slopes can be classified
into four types;
1. Circular or Rotational
mode of failure,
2. Plane mode of failure,
3. Wedge mode of
failure,
4. Toppling mode of
failure,
5. Raveling slopes or falls and
6. Rock Falls.
12

Landslide Features
103

17
EFFECTS AND LOSSES DUE TO LANDSLIDES
104
A) Direct Effects:
Physical Damage-Debris may block roads, supply lines (telecommunication,
electricity, water, etc.) and waterways.
Causalities- deaths and injuries to people and animals.
B) Indirect Effects:
Influence of landslides in dam safety- failure of the slopes bordering the reservoir,
Flooding caused by movements of large masses of soil into the reservoir.
Landslides and flooding- Debris flow can cause flooding by blocking valleys and
stream channels, forcing large amounts of water to backup causing backup/ flash
flood.

18
C) Direct losses:
Loss of life, property, infrastructure and lifeline facilities, Resources,
farmland and places of cultural importance.
D) Indirect losses:
Loss in productivity of agricultural or forest lands, Reduced property
values, Loss of revenue, Increased cost, Adverse effect on water quality
and Loss of human productivity
105

23
106

24
107

25
ENGINEERING CONTROLS
• Designing the cut slope.
• De‐pressuring the slope.
• Improving Drainage of the slope.
• Engineering Retaining structures.
• Surface protection.
• Reinforcement of slope.
108

26
Improving Drainage of Slope
 In most of the cases water saturation induce instability in
slope.
 For this reason only most of the slopes fail during rainy
season.
 During rainy season there is a considerable recharge of
ground water.
 In soil slope water saturation can;
 Considerably Increases the weight of soil – Increase in
driving force
 Development of pore water pressure – Increase in driving
force
 Reduction in shear strength
109

Improving Drainage of Slope
 In Rock slope water saturation can;
– Develop water forces along potential failure plane –
uplift water force – reduction in normal stress –
reduction in shear strength
– Lubricates the failure surface – ease for sliding mass.
Thus, controlling or improving surface drainage
improves the stability of slope
110

Surface drainage of a slope
Internal drainage gallery in
restored slope
111

Engineering Retaining structures
112
• Generally, retaining structures are not particularly effective methods.
• Difficult to construct on an already moving slide.
• One use of them, though it is used to ensure complete stability of an
existing (old) landslide, which may in the future be reactivated.
• We estimate the force acting on a retaining wall by using the interslice
forces from stability analysis.
• The wall provides additional resistance which is only mobilized by further
deformation of the slope.
• The force then acts along the line of action (see figure) into the soil or rock
beneath the slope.
27
Retaining structures

Permanent retaining structures;
1. Gravity retaining wall
2. Semi gravity retaining wall
3. Cantilever retaining wall
4. Counter fort retaining wall
5. Berm below the toe.
Temporary retaining structure
1. Gabbions
2. Bracings in the soil cut
3. Sheet pile (Bulk head) walls
Engineering Retaining Structures
113

114
Engineering Retaining Structures
In soil slopes considerable stability can be attained by providing
retaining structures.
 Permanent retaining structures
 Temporary retaining structures
Permanent retaining structures;
 Gravity retaining wall- These walls
depends upon their weight for
stability.
 Semi gravity retaining wall-small
amount of reinforcement is provided
near the back face
 Cantilever retaining wall -are made of
reinforced cement concrete. The wall
consists of a thin stem and a base slab
cast monolithically.

30
Vegetation Cover – Surface Protection
 Plant roots and vegetation cover may stabilize the underlying slope
 by reducing the pore water pressure through Evapo‐transpiration,
 Intercept direct impact of precipitation and reducing the effective
surface area to reduce percolation
The plant roots tightly strengthen the underlying soils.
 The big tree species if planted in the upper slope, it may increase
the load over the critical slopes.
 type of vegetation species to be planted over slope face, should be
identified and supported with site specific scientific research.
115

31
Summary Landslide Mitigation
Before making a choice to adopt a suitable mitigation
measure for a given landslide prone area following has to
be considered;
1. Possible mode of failure –
2. Slope Material Type
3. Technical feasibility of Remedial measures
4. Financial Consideration
5. Degree of Risk
116

Landslide Hazard in Ethiopia
117
• Over 700 landslide sites recorded in
Ethiopia; mostly affecting rural
communities, infrastructures, farm
lands, dwelling houses
(KifleWoldearegay,2013).
Earth slide along Jimma-Agaro road
• landslide has been a frequent
problem in Ethiopia spatially in the
high land north, south, western
and rift escarpment valley (Ayele et
al.,2014).
Landslide Hazard in Ethiopia

Landslide type, factors ,distribution and effects in Ethiopia
118
Landslide type in highland of
Ethiopia
Types of landslides triggered by rainfalls
in the highlands of Ethiopia include:
debris/earth slides,
debris/earth flows, and
rockslides. But
Along Shire-May Tsebri
road
Tarmaber area,
Feresmay area
Jimma
area
Mush area
rock fall& toppling have little
association with rain fall
Kifle Woldearegay(2013)
Adishu
area
(Debreberhan)

landslide controlling factors in the highlands of Ethiopia
119
Most of the slope failures in the highlands of Ethiopia a
happened because of
produced by Ayalew
(1999), Woldearegay
et al. (2005), and
Woldearegay (2005).
rainfall
geological (lithological and structural)settings,
slope shapes,
slope gradients,
Drainage lines(stream incisions/gullying) and
Slope modification, and
vegetation cover.

2.2. Settlement
120
 Settlement is the downward
movement of a building to a
point below its original position.
 Foundation settlement is usually
the result of the shifting or
compaction of the underlying
soil, often due to construction on
backfill or changes in soil
conditions and moisture content.
41

Causes of settlement
121
42
 The causes of foundation settlement are rarely due to the
design of the structure itself. More commonly, damage is
caused as changes occur within the foundation soils that
surround and support the structure.
 The most common causes of foundation settlements are:
1. Weak bearing soils
• Some soils are simply not capable of supporting the weight or
bearing pressure exerted by a building's foundation. As a result,
the footings sink into the soft soils.
• Majority of settlement problems caused by weak bearing soils
occur in residential construction, where the footings are designed
based upon general guidelines and not site-specific soil
information.

Cont’d
122
43

Cont’d
123
2. Poor compaction
• When fill soils are not adequately compacted, they can
compress under a foundation load resulting in settlement of
the structure.
• In general, before a foundation can be constructed, properly
placed and compacted fill soils can provide adequate support
for foundations.
44

Cont’d
124
45
3. Changes in moisturecontent
• Extreme changes in moisture content within foundation soils can
result in damaging settlement.
• Excess moisture can saturate foundation soils, which often
leads to softening or weakening of clays and silts. The reduced
ability of the soil to support the load results in foundation
settlement.
• Increased moisture within foundation soils is often a consequence
of poor surface drainage around the structure, leaks in water lines
or plumbing, or raised groundwater table.
• Soils with high clay contents also have a tendency to shrink with
loss of moisture. As clay soils dry out, they shrink or contract,
resulting in a general decrease in soil volume.

Cont’d
125
46

Cont’d
126
47
4. Maturing trees and vegetations
• Maturing trees, bushes and other vegetation in close proximity to a
home or building are a common cause of settlement. As trees and
other vegetation mature, their demand for water also grows.
• The root systems continually expand and can draw moisture from
the soil beneath the foundation. Again, clay-rich soils shrink as
they lose moisture, resulting in settlement of overlying structures.
Many home and building owners often state that they did not have
a settlement problem until decades after the structure was built.
• This time frame coincides with the maturation and growth of the
trees and vegetation.

Cont’d
127
• Foundations closer to the surface are more often affected by soil
dehydration due to tree roots than are deep, basement level
foundations.
48

Settlement
…
128
49
5. Soil consolidation
• Consolidation occurs when the weight of a structure or newly-
placed fill soils compress lower, weak clayey soils. The applied
load forces water out of the clay soils, allowing the individual soil
particles to become more densely spaced.
• Consolidation results in downward movement or settlement of
overlying structures. Settlement caused by consolidation of
foundation soils may take weeks, months, or years to be
considered "complete."
• As this occurs, the foundation will experience downward
movement -- sometimes at an uneven rate. This leads to
cracks and structural damage.

Cont’d
129
50

2.3. Subsidence
130

2.3. Subsidence
131
• Displacement of the ground
surface vertically over broad
region or localized areas.
• Natural or human-induced
• Slow settling or rapid collapse
• Causes:
– Extraction of GW, natural
gases and oils
– Underground mining
– Dissolution of LST
– Earthquake
– Faulting induced
– Sediment loading

Cont’d
132
52

1. Dissolution of limestone
133
53
• Dissolution of limestone by fluid flow in the subsurface
causes the creation of caves or karast.
• This type of subsidence can result in sinkholes which can be
many hundreds of meters deep.
2. Mining
• Sub-surface mining which intentionally cause the extracted
void to collapse will result in surface subsidence.
3. Extraction of natural gas
• If natural gas is extracted from a natural gas field the initial
pressure in the field will drop over the years.
• The gas pressure also supports the soil layers above the field. If
the pressure drops, the soil pressure increases and this leads to
subsidence at the ground level.

4. Earthquake
134
54
• Caused displacement of earth’s crust due to internal and
external causes => subsidence
5. Groundwater related subsidence
• Groundwater table fluctuation leads to subsidence
6. Fault induced
• When differential stresses exist in the Earth, either by geological
faulting in the brittle crust, or by ductile flow in mantle.
• Where faults occur, absolute subsidence may occur in the hanging
wall of normal faults. In reverse, or thrust, faults, relative
subsidence may be measured in the footwall.

7. Sediment loading
135
55
• The mass added due to deposition or excavational fill of soil
increases the compaction degree of underlying soft rocks =>
subsidence.
8. Seasonal effects (expansive clays)
• soils containing significant proportions of clay affected by
changes in soil moisture content.
• Seasonal drying of the soil results in a reduction in soil
volume. If building foundations are above the level to which
the seasonal drying reaches they will move and this can result
in cracking the building.
• Shrinking and swelling of soil and soft rock requires two
conditions to be satisfied before it occurs.
1. The soil or rock must have the potential for volume change.
2. Adequate amount of water

Mitigating the effect of subsidence
136
56
• Avoiding withdrawal overdraft from compressible GW aquifer
• Controlling land-use to avoid subsidence in areas underlain by
soluble rocks.
• Extraction of hydrothermal can be re-injected with water
• Sealing sinkholes, restoring the ground surface and promoting of
GW flow away from sinkholes.
• Avoiding founding structures on expansive soils.

J. David Rogers
2.4. Hazards from expansive soils:
Introduction to clay mineralogy, Origin of
expansive soils,
Tropical soils and engineering,
Climate-soil interaction and ASSIGNMENT 3
impacts on engineering works,
Expansive soils in Ethiopia,
Mitigation measures of expansive soil hazards
137

Expansive Soils
138
 Expansive soils are typically clayey soils that
undergo large volume changes in direct
response to moisture changes in the soil.
 Expansive soils are those
containing sufficient quantities of clay
minerals (Montmorillonite, Kaolite,
Illite, vermiculite and soon) which
tend to swell when they absorb
moisture and shrink when they lose
moisture.
 A pattern of polygonal desiccation, or
“shrinkage cracks”, results, as seen at
left.
• These soils possess a high plasticity
index.
• The cracks travel deep into the
ground.

• Sidewalk heave is a common manifestation of expansive soils
at foundations.
• Excessive watering, leaky irrigation systems, and/ or poor
drainage often highlights this problem.
139

• Poor drainage adjacent to
slabs and flatwork is a
common problem is
expansive soils-related
damage
• Difficult to solve in flat-lying
flood plains
140

• Signs of expansive soils behavior include lifting of lighter
structural elements, as opposed to heavy elements, such as
chimneys. Edge lift at corners and shear cracking near corners
is also common.
141

Fig, When clay materials getting dry, Develop deep Cracks around 0.8m
142

8
The entire ground is collapsed due to expansive soil
143

Cont’d
144
Evaluating expansive soils
• Common methods for identifying expansive soils on the basis of volume-change
characteristics or related physical properties are:
1. Atterberg limits test, 2. Free swell test
3. Colloid-content determination, 4. linear shrinkage test
• The geotechnical engineer needs to identify the soils that are likely to collapse and
determine the amount of collapse that may occur.
• Some soils at their natural water content will support a heavy load but when water is
provided they undergo a considerable increment in volume
• The amount of collapse is a function of the relative proportions of each component
including degree of saturation, initial void ratio, stress history of the materials,
thickness of the collapsible strata and the amount of added load.

Swelling Potential
145
The three ingredients generally necessary for potential swelling to
occur are:
1. Presence of montmorillonite/smectite in the soil,
2. The natural water content must be around the PL, and
3. There must be a source of water for potential swelling clay
Table : Probable expansion as estimated from classification test data

Foundations on collapsing soils
146
 Identification of collapsing soil is highly crucial
• All collapsing soil contain an appreciable percentage of air in the voids.
• Collapsing soils compress significantly even during sampling by tubes.
• Collapsible soils usually slake upon immersion, but disintegration by slaking
is not a definitive indicator because other types of soils also slake.
• Swelling potential is related to plasticity index.
• Final decision should be based on consolidation test, load test conducted

Collapsing soil can cause settlement:
147
– Total settlement = immediate settlement + primary consolidation
settlement + secondary compression settlement
– Differential settlement = non-uniform settlement
 The severity of settlement and impact to structures which can result
from collapse of the sub-soils depends on several conditions.

Settlement on soil stratum
148
• Imagine a soil layer with thickness H is loaded.
• The following settlement occurrences can be observed:
1. Rapid reduction of thickness H, due to elastic deformation (immediate
settlement, Si);
2. Further reduction of H, due to expulsion of water from the voids
(primary consolidation settlement, SC). This is a very slow process
and continues over a long period;
3. Further reduction of H, due to plastic re-adjustment of soil (solid)
grains (secondary compression settlement, SS)
• The figure below illustrates the three phases of settlement over
time.

Figure: three phases of settlement for fine-grained soils as function of time.
149

Settlements of foundations
150
No settlement Total settlement Differential settlement
• Uniform settlement is usually of little consequence in a building,
• Differential settlement can cause severe structural damage.

Cont’d
151
Differential Settlement due to variable soil types

152
Expansive soils in Ethiopia
 In Ethiopia expansive soil are formed over the tertiary to recent basaltic volcanic rocks.
 They are contain montmorillonite as principal clay minerals and with accessory kaolinite and
halloysite.
 They are formed from the weathering of basic volcanic rocks which cover the Ethiopia
plateau.
 They usually have high silica-oxide ratio and also high amount of Fe, Ca, and Mg.
 Most of the expansive soils met in nature have clay size fraction (less than 2 micron size)
varying between 40% and 75%, silt size varied between15% to 30%, sand varied between15%
to 30% and gravel size less than 5%.
 Expansive soil is found anywhere in the world and distribution of expansive soil is generally a
result of geological history, sedimentation and local climatic conditions.

153
In Ethiopia, covering nearly 40% surface area of the country, expansive soils are observed in
area such as central Ethiopia, following the major trunk road like Addis Ababa - Ambo, Addis
Ababa - Weliso, Addis Ababa – Debere Birhan, Addis Ababa - Gohatsion, Addis Ababa -Mojo.
Also the cover the area like Mekelle, Bahirdar, Gambela, Arba Minch and the most Southern,
South-west and south-east part of the capital Addis Ababa area in which the most major recent
construction are being carried out. The distribution are showed in figure below.
Distribution of Expansive Soils in
Ethiopia

154
The properties of significance in performance of clays and shales in construction
engineering are:
I. Static properties of earth materials:
A. Particle-size distribution,
B. Unit weight,
C. Void ratio,
D. Specific gravity of the constituents,
E. Fluids content
II. Dynamic properties of earth materials:
A. Consistency,
B. Permeability,
C. Thixotropy,
D. Shear resistance,
E. Compressive strength,
F. Volume change (1. Consolidation with loading, 2. Swelling with hydration, 3. Drying
shrinkage, 4. Syneresis, 5. Frost heaving),
G. Sensitivity to remolding,
H. Slaking,
I. Electro-osmosis,
J. Thermo-osmosis

Mitigation measures of expansive soil hazards (Treatment of the
effects of expansive soils)
155
• The best mitigation method for the effects of expansive soils to avoid
founding on them. However, their extensive occurrence in some areas
make it infeasible.
• Some of the methods are;
1. Removing the expansive soil and replace it with non-expansive soil.
thickness may be too big to permit complete removal. Removal of
expansive soils and replacement with non expansive sand-gravel soil
used to avoid damage.
2. Foundation treatments: applying confining load is one type of foundation
treatment. This involves placing a blanket or embankment of non
expansive soil over expansive soil. The surcharge resists the uplift
pressure of underlying expansive soil. This is effective for large buildings.
3. Another foundation treatment is placing reinforced concrete piers
below the depth of expansive soil.

Cont’d
156
4. Chemical stabilization of expansive soil: to modify the ionic
character of soil and water preventing swelling.
a. Hydrated lime (Ca(OH)): Strong Ca2+ replaces weak Na1+ on the
surface of clay particles. This reduces base-exchange capacity of clay
=> lower volume-change potential.
b. Portland cement: it has two separate effects. The lime within the
cement acts in the same way as hydrated lime. Besides, the hardened
cement matrix in the soil resists movement.
5. Isolating water from expansive soils. Depend on whether surface water
(ditches and pipes) or ground water used to keep water away from the
sensitive area. Sand and gravel is used to break in capillary continuity
when GW is moving upward. Enveloping masses of expansive in
impermeable membrane is good isolating of water.
6. Deep vertical geomembranes/moisture barriers: effective in highways.
Moisture barriers are constructed in trenches filled with gravel or
impervious membrane.

Chapter
Outline
157
CHAPTER III
Engineering works and subsurface water
• Effects of subsurface water on engineering structures
• Water quality and engineering work
• Controlling techniques of subsurface water effect

At the end of this chapter
158
CHAPTER III
Engineering works and subsurface water
GEOTECHNICAL INVESTIGATION
 Geological Media
– Ground
• Soil
• Rock
– Groundwater
• Students will be able to understand the interaction of subsurface water
with earth material and its effect on engineering structures
• Students will be acquired knowledge to reduce the effects of
subsurface water on engineering works

Introduction to Subsurface water
159
• Ground water: the water that lies beneath the ground surface,
filling the pore space between grains in bodies of sediment
(soils) and clastic sedimentary rock, and filling cracks,
discontinuities and cavities in all types of rock.
• The subsurface water can flow in different direction depending
on its level and subsurface structures.
• This subsurface flow is facilitated where there is hydraulic
head.
• The flow can be towards or away from engineering structures,
hence it affects the performance of the structures.

Effects of subsurface water on engineering Structures
160
• Engineering structures like dam, building, highways,
railways, roads and other underground projects such as
mining, tunnels could be affected by the water (surface or
subsurface) in different ways .
• It may pose problems during
• construction stage,
• its performance stage and
• reduce the safe functioning of an engineering project.
• Engineering project can also affects the subsurface water by
altering its quality and flow direction.

The Main Effects of Subsurface Water on Engineering Structures are:
161
• Eroding the foundation of structures
• Volume change of soil or rocks of the foundations which is resulted in
Settlement or collapse.
• Increasing moisture of slope material that resulted in the sliding of slope by
reducing safety factors.
• Affect excavation and construction activities when it flowing towards the
structures to be constructed.
• Reducing the bearing capacity and shear strength of a material on site.
• Lubricating the contacts between layers or weak zones.
• leakage towards the structures and develop uplift pore pressure which
results in the failure of engineering structures.

162
• Generally, sub surface water would be resulted in flooding, swelling
of expansive materials, reduction in bearing capacity, uplift
pressures, chemical attack and difficulties during construction due to
flooding to the site.
activities of subsurface water on Engineering structures.
• The following information should be collected properly during site
investigation
 Distribution and content of sub-surface water.
 Direction and velocity of subsurface water flow in the site
 Depth to water table and its range of fluctuation under
different condition.
 Regions of confined, perched and unconfined water levels.
 Hydro-chemical properties and pollutants that can decompose
the engineering structures.

Effects of Subsurface Water on Dam Site
163
• Subsurface water is the most and critical problems in the
foundation and abutments of dam project.
• Because in most cases, dam foundation will be situated to
placed at great depth below subsurface water in order to
reduce instability problems.
• In this case, there will be an inflow of water into the
excavation, which may block or retard the construction
activities.
• Rock mass contains discontinuity may serve as reservoir
and conduit for ground water that may pose problems
during excavation.

164
 Subsurface water conditions in dam projects will be
causes
• Seepage into the storage.
• Water over flow.
• Failure of a dam and flooding downstream side.
• Increase pore water pressure within foundation and
abutments, which is responsible in the reduction of
cohesion/resisting force .
• Pose problems in excavation and construction activities.
• Erode foundation and damage the structure of the dam.
• lubricate the discontinuity and facilitate the failure of
dam abutment.

165
• Subsurface water fluctuations may cause uplift problems
in the dam foundation area which in turn responsible for
the settlement.
• Sub surface water can bring different dissolved chemical
to the foundation, which can react with construction
material and damage overall structures
Generally, dam failures can be grouped into four
classifications which may or may not related to subsurface
water effect:
– Overtopping,
– Foundation failure
– Structural failure and
– Other unforeseen failures.

166
• The water near the tunnel can develop pore water pressure around
the tunnel and can results in collapsing of a tunnel.
• The water can saturate the roof of the tunnel passage and results in
ground collapse by reducing the withstand capacity of the soils.

Effects of Subsurface Water onTunnel
167

Effects of Subsurface Water on Building Foundations
168
• Temporary or permanent rising and lowering of the groundwater table
from man-made or natural causes an effect on buildings, streets,
underground utilities and other structures.
• Foundation / base of every engineering structure are on or in the soils
or rocks.
• When the rocks and soils exposed to subsurface water their
engineering properties can be changed by saturation and pore pressure
effects.
• This effect is results in the reduction of bearing capacity, shear
strength, durability, hardness of soils and rocks.
• Generally the effects of ground water on the stability of foundations
are pore water pressure/uplift, saturation of foundation rocks and soils,
dissolving cementing material, developing slippery base and swelling
effects. Wollo University, Ethiopia Elias A.

Effect of Sub Surface Water on Pavements
169
• The stability of pavements depend on the presence of
ground water, and types of construction material.
• When the ground water level reaches the base of the
pavement it will have an effect like saturation, reduce the
adhesion in construction material and reduce the strength
of the materials on foundation.
• The fluctuation of subsurface water makes the swelling
and shrinkage of sub grade of the pavements, which in
turn reduce the bearing capacity of the soils.
• During the fluctuation of sub surface water the soil under
the structure is equally saturated and the soils under the
shoulder dry faster than the other and form a crack
parallel to the road on the side of the roads.

170
• Thus subsurface water bring a distress of pavement.
• Moisture variation and frost action are the main cause of
deterioration of the subgrade.
• When the water content is decreased,
shrinkage cracks develops, which
cause differential settlement in the
rigid pavement and cracks in the
flexible pavement.
• Hence the pavement should be
provided with a suitable drainage
system or the pavement must be
constructed above the maximum level
of the ground water table to keep it
dry.

Water Quality and Engineering Structures
171
• Water chemistry- the chemistry of subsurface water can varies
from place to place and from time to time, because it depends on
the material through which it exists or in what chemistry it exist.
• The chemistry of sub surface water are measured in terms of
acidity and total dissolved solid (TDS).
• Depend on the chemistry, subsurface water is the most dissolving
agents on engineering structure which responsible for the formation
of karst, solution cavities.
• This results in the collapsing of structure on the surface above the
karst or solution cavities.
• Also the water can react with carbonate rocks along its path, this
reaction results in the formation of carbonic acid, which is
chemically acidic and easily react with construction materials such
as concrete. Wollo University, Ethiopia Elias A.

172
• Sulfuric acid also formed when water react with some
evaporate rocks such as gypsum.
• The sulfuric acid will facilitates the weathering process of
the native foundation rock causing decrease in strength.
• When Sulfate present in large amount, is aggressive to
concrete, metallic structures, like rock bolts, steel used as
reinforcement etc.
• This ability water to deteriorate, weathering and eroding
of structure due to its composition is known as
corrosivity.
• In corrosive subsurface water conditions, while doing
excavations, a proper precaution has to be taken to reduce
the effect of corrosion, especially in permanent
excavations. Wollo University, Ethiopia Elias A.

173
 Chemistry of ground water affects stability of engineering
structures because of
• Formation of cavern- when water dissolve the carbonate rocks.
– Most caves are formed by the chemical dissolution process.
• Sinkhole-form as a result of lowering the water table by excessive
pumping for human use of the water. Or by dissolving of underground
support.
• Subsidence- results from withdraws of fluids or collapse of underground
caves

Controlling Subsurface Water Effects
174
Why Drainage & Dewatering?
• Carryout construction activity below water table.
• To increase stability of soil.
• To decrease seepage & pore water pressure.
• Reclamation of water logged areas.
• Release of hydrostatic pressure behind the retaining
structures.

Controlling Subsurface WaterEffects
 Shallow well system

 Deep well system
 Vacuum method
 Electro-osmosis method
175
1. Lowering Water Table
 Ditches & sumps
 Well point system
 Sheet pile
 Ground freezing
Grouting
2. Water Exclusion Method

Ditches & Sumps
176

Deep well Drainage System
177

Vacuum Method
178
• Useful for fine grained soils
• (fine, non cohesive soils, Silty sands etc.) particle size D10 is smaller than
0.05mm & its co-efficient of permeability between 10 -3 and 10-5 cm/s.
• It is necessary to apply a suction head in excess of the capillary head to
the dewatering system.
• A hole of 25 cm dia. is created around the well point and the rise pipe by
jetting water under sufficient pressure.
• Vacuum pumps are used to create a vacuum in the sand filling.
•When the vacuum is drawn on the well point, the ground
surface is subjected to unbalanced atmospheric pressure

3. Drainage by Electro-Osmosis
179
• Used in cohesive soils
• +ve water particles electrostatically bound to –ve soil particles
makes dewatering difficult
• Direct current is passed between two electrode in to saturated soil
mass to break attraction and allow water to flow.
• Soil water travel from positive to negative Cathode made in a form
of well point or a metal tube for pumping out the seeping water.
• Natural flow of water is reversed away from the excavation
• Thereby increasing shear strength of the soil and stability of the
slope
• Very costly
• Used where the main purpose is to increase consolidation and
shear strength of the soil

Water Exclusion
180
1. Sheet Piles/Secant Piles/Diaphragm Wall
• Dual purpose (providing
impermanent support to
excavation and excluding
groundwater)
• The pile block the movement of
water towards the excavation/
construction area and support the
side of excavation.
• The water pressure can
develop and result in failure
of the wall, if it is not well
designed.

2. Grouting
181
• Used where permeability is too high or where access is
difficult (tunnelling)
• Grout is injected of cement into the soil under pressure
via boreholes or drill holes
• May be cementitious, chemical (silica based) or bentonite.
• Can strengthen soil and / or form impermeable barrier.

1
CHAPTER IV
182
 Dams and Reservoirs
 Tunnels
 Roads, Bridges and Railways
Significance of Engineering geology in Engineering
Hydraulic structures

183
Hydraulic Structures are engineering constructions designed and mechanically fit for managing and
utilizing water resources to the best advantage of the human being and environment.
Dam is a barrier across flowing water that obstructs, directs or retards the flow, often creating a Reservoir.
Reservoir is an artificial lake created by flooding land behind a dam. Some of the world's largest lakes
are reservoirs.
Spillway is a section of a dam designed to pass water from the upstream side of a dam to the downstream
side. Many spillways have gates designed to control the flow through the spillway.
Flood is an overflow or an expanse of water submerging land.
 Dams differ from all other major civil engineering structures in a number of important regards:
 Every dam, large or small, is quite unique; foundation geology, material characteristics, catchment
flood /hydrology etc. are each site-specific.
 Dams are required to function at or close to their design loading for extended periods.
 Dams do not have a structural lifespan; they may, however, have a notional life for accounting
purposes, or a functional lifespan dictated by reservoir sedimentation.
 The overwhelming majority of dams are of earth fill, constructed from a range of natural soils; these
are the least consistent of construction materials.
 Dam engineering draws together a range of disciplines, e.g. Structural and fluid mechanics, geology
and geotechnics, flood hydrology and hydraulics, to a quite unique degree.
 The engineering of dams is critically dependent upon the application of informed engineering
judgment.
 Hence the dam engineer is required to synthesize design solutions which, without compromise on
safety, represent the optimal balance between technical, economic and environmental considerations.
Hydraulic Structures

2
Dams
184
 Dams are civil engineering structures build across the river valley to impound large
volume of water to be used for single or multipurpose use of; power generation,
irrigation purpose, flood control, ground water recharge and water diversion.
 The most common reasons for building dams are
 to concentrate the natural fall of a river at a given site, thus making it possible to
generate electricity;
 to direct water from rivers into canals and irrigation and water-supply systems;
 to increase river depths for navigational purposes;
 to control water flow during times of flood and drought; and
 to create artificial lakes for recreational use.

Wollo University, Ethiopia Elias A. 185
Important Terminology of The Dam (parts of the dams)
 Heel of the dam: It is the part where the dam comes in
contact with the ground on the upstream side
• Toe of the dam: It is that part where the dam comes in
contact with the ground on the downstream side
• Free board: It is the difference in level between the top of
the dam wall and the highest storage level.
• Galleries: These are small rooms left within the dam for
checking operations.
• Spillway: An arrangement is made in a dam near the top or
inside to allow excess water of the reservoir flow to the
downstream side
• Sluice (outlet conduit): It is an opening in the dam near the
ground level. It is useful in clearing the silt of the reservoir.
• Cut-off wall: It is an underground wall-like structure of
concrete in the heel portion. It is useful in preventing leakage
under the foundation.
• Abutment: These are the sides of the valley on which the
dam structure rests.
• Parapet walls: Low Protective walls on either side of the
roadway or walkway on the crest.
• Dead Storage level: The portion of total storage capacity
that is equal to the volume of water below the level of the
lowest outlet (the minimum supply level).
• Diversion Tunnel: Tunnel constructed to divert or change
the direction of water to bypass the dam construction site.
• Tail water: water at the downstream base of the dam
resulting from the backup of water discharged from the
spillway or powerhouse.

186
 Classification according to material of construction
 Timber dams
 Steel dams
 Concrete dams
 Earth dams
 Rock fill dams
 Combined dams
 Classification according to design criteria
Hydraulic design Stability consideration
Non-overflow dams Gravity dams
Over-flow dams Non-gravity dams
Composite dams
 Classification according to Purpose
Storage dams Stage control dams Barrier dams
Flood control Diversion Levees and dykes
Water supply Navigation Coffer dams
Detention storage
When the size of the dam has been determined, the type of dam envisaged requires certain
geological and topographical conditions which, for the main types of dams, may be stated as
follows.
Concrete Dams Embankment Dams
 Gravity dams Rock fill dams
 Buttress dams Hydraulic fill dams
 Multiple arch dams Earthen embankments
 Thick arch dams Composite dams
 Thin arch dams Wollo University, Ethiopia Elias A.
DAM TYPES

187
A. Gravity
B. Arch
C. Buttress
D. Embankment
5
Concrete, rubble masonry
Concrete
Concrete, also timber & steel
Earth or rock
Dams are classified on the basis of structural form and materials used.
Types Materials of Construction
 The first three types usually are built of concrete.
Classification according to height (H)
 H ≤ 30m low dam
 30 ≤ H ≤ 100m medium
 H ≥ 100m high dam

188
Factors governing selection of types of dam
1. Topography-Valley Shape
A Narrow V-Shaped Valley: Arch Dam
A Narrow or Moderately with U-Shaped Valley: Gravity/Buttress Dam
A Wide Valley: Embankment Dam
2. Geology and Foundation Condition
Solid Rock Foundation: All types
Gravel and Coarse Sand Foundation: Embankment/Concrete Gravity Dam
Silt and Fine Sand Foundation: (earth) Embankment/ low concrete Gravity Dam
but not rockfill
Clay foundation: earth dams
3. Cost
 availability of construction materials near the site; accessibility of
transportation facilities

Cont’d
189
1. Gravity Dams:
• These dams are heavy and massive
concrete wall structure in which the
whole weight acts vertically downwards.
• rigid monolithic structure
• Gravity dams are dams which resist the
horizontal thrust of the water entirely by
their own weight.
• Minimal differential movement tolerated
• Dispersed moderate stress on valley floor
and walls
Reservoir
Force
•As the entire load is transmitted on the small area of foundation, such
dams are constructed where rocks are competent and stable.
•The weight of rock and concrete structure to hold back the water in the
reservoir.
6

190

Cont’d
191
3. Uplift
The water under pressure that comes b/n dam and foundation and results
in upward (uplift) forces against the dam.
h1 = depth of water @ upstream face, “heel” (higher)
h2 = depth of water@ downstream face, “toe” (lower)
Υ = specific weight of water
t = base thickness of dam
4. Ice pressure
t
U  
h1 h2
2
Pressure created by thermal expansion exerts thrust against upstream
face of the dam
5. Earthquake forces
Results in inertial forces that include vertical motion, oscillatory
increase, or decrease in hydrostatic pressure (all put force against dam)
Causes of Failure GD:
1. Sliding along horizontal plane (shear failure)
net force > shear resistance at that level
2. Rotation about the toe
3. Failure of material

192

193
ADVANTAGES
 External forces are resisted by weight of dam
 More strong and stable
 Can be used as overflow dams also with spillway feature
 Highest dams can be made as gravity dam’s because of its high stability
 Specially suited for heavy downpour; slopes of earthen dams might get washed away
 Less maintenance required
 Gravity dam does not fail suddenly but earthen dams
DISADVANTAGES
 Can be made only on sound rock foundation
 Initial cost is high
 Takes more time to construct if materials are not available
 Requires skilled labour.

2. Buttress Dam:
194
This type of structure can be considered even if the foundation rocks are little weaker.
A buttress dam has an upstream face or deck to support the impounded
water, and a series of buttresses or triangular vertical walls built to
support the deck and transmit the water load to the foundation. These
dams are sometimes called hollow gravity dams because they require
only 35 to 50 per cent of the concrete used in a solid gravity dam of
comparable size.

195
Types of buttress dam
I. The flat slab type Buttress Dam. In this
type the concrete deck slab spans the
distance between adjacent buttresses.
II. The Multiple Arch Type Buttresses. In this
type each unit of the water supporting
member is an inclined arch barrel supported
by the buttresses.
III. The Massive Head Type. In this type the
water supporting member is merely an
enlargement of the upstream head of the
buttresses.

196
Advantage
 Retain water between buttress
 Less massive than gravity Dams
 When future increase in reservoir; Future extension is possible by
extending buttress and slab
 Power house can be made B/W buttress; thus reducing cost
 Can be designed to accommodate moderate movement of
foundation without any serious damage.
Disadvantages
 Skilled labor requirements
 Deterioration of u/s as very thin concrete face

 High strength concrete or masonry wall
 convex face upstream.
 Huge stresses imposed on valley walls and floor
 Utilize the strength of an arch to displace the load of water behind it onto the
rock walls that it is built into.
 This shape helps to transmit the major part of the water load to the abutments
 Arch dams are built across narrow, deep river gorges,
3. Arch Dams:
197

198

199
Advantage
 Curved in plan
 Carried load horizontally to it’s by arch action
 Balance of water load is transferred to the foundation by cantilever
action
 Adapted in gorges where length is small in proportion to height
dam require less material can be made in moderate foundation
because of load distribution as compared to gravity dams.
Disadvantages
 Require skilled labor
 Speed of construction is slow
 Require strong abutments of solid rock of resisting arch thrust.

200
Embankment dam can be classified into two
1. Earth Dams
are the most simple and economic (oldest dams)
Types:
I. homogeneous embankment type;
These dams are constructed with uniform and homogeneous materials. It is suitable
for low height dams (up to 10m). These dams are usually constructed with soil and
grit mixed in proper ratios.
II. Zoned embankment type
These are dams with the central portions called core or hearting made from
materials which are relatively impervious. The thickness of the core wall is made
sufficiently thick to prevent leakage of water through the body of the dam.
An Embankment Dam is a freshwater-retaining structure comprising excavated rock, soil, or a
combination of rock and soil from nearby geological formations. In fact, Embankment Dams
are known as an “Earth-fill Dam” when filled with soil, and a “Rockfill Dam” when filled with
rocks. Earth-fill Dams are most common.

201
Homogeneous embankment type
Zoned embankment type

General view of an Earth-fill dam

203
2. The rock fill dam
Consist of three basic elements;
I. a loose rock fill dump, which constitutes the bulk of the dam and resist the thrust
of the reservoir.
II. Impervious facing of the upstream slope with concrete, timber, steel
III. Rubble masonry between (i) and (ii) to act as a cushion for the membrane and
resist destructive deflections
Advantage
• Made of locally available gravels
• Can be made on any type of available foundation
• Can be constructed rapidly
• Cheaper
• Future consideration can be made (raising height)
Disadvantages
 Vulnerable to damage by floods
 Cannot be used as overflow dams not suitable where heavy downpour is more
common
 High maintenance cost

204
While selecting a site for a dam the following points should be taken into
consideration
I. The dam should be as near as possible to the area to be served, hence
conveyance cost and water losses will be minimized.
II. Foundation area should be impervious and should be able to support the
weight of the dam.
III. The topography of the dam and reservoir sites should permit maximum
storage of water at minimum cost.
IV. Materials of construction should be available in sufficient quantity and
good quality at a reasonable distance.
V. The value of property and land which will be submerged by the
reservoir has to be as small as possible.
vi. The cost of relocating roads, buildings etc. should be as small as possible
vii. The cost of stream diversion and dewatering the site should be as small
as possible
viii. Transportation facilities and accessibility of the site
ix. Availability of suitable sites for construction equipment and camps
x. The safety of the structure.

Engineering geological consideration in dam construction
205
I. Reconnaissance study
1. Evaluation of the data having at archives
2. Field investigation for limited time (Reconnaissance Study)
3. Some maps in small scale, for example 1/25.000 or 1/50.000
4. Some hydraulic data about
a. Basin
b. Precipitation area
c. Runoff, maximum discharge {Q=R/t (m3/s)}
5. Some approach to the reservoir area, dam site and type of dam
and height of dam...etc
6. Photogeological studies

Cont’d
206
II. Preliminary Studies At The Reservoir Area And Dam Site
1. Dam site investigations
1. Location of dam axis
2. Location of diversion tunnel
3. Location of spillway
4. Location of powerhouse...etc
2. Geological studies
3. Geophysical surveying
4. Underground investigations
1. Boreholes
2. Drilling tests
5. Surveying for materials
1. Field surveying
2. Laboratory tests
6. Slope stability investigations
7. Earthquake hazard & risk
analysis
8. Environmental studies
9. Leakage possibilities from
reservoir area
10. Leakage possibilities from
dam site
11. Erosion, sedimentation &
siltation

207

208

209

210

211

212
Introduction: definitions and concepts of reservoir
Reservoir: a water body or lake which could be created when a barrieris
constructed across a river or a stream.
Advantages/uses of reservoirs:
 Water supply.
 Irrigation.
 Hydroelectric power generation.
 Recreation.
 Flood control.
 Navigation, and others.
Disadvantages of reservoirs:
 Detract from natural settings, ruin nature's work.
 Inundate the spawning grounds of fish, and the potentialfor archaeological
findings.
 Inhibit the seasonal migration of fish, and even endangersome species of fish.
 Foster diseases if not properly maintained.
 Water can evaporate significantly.
 Induce earthquakes.

213
Factors that affect Reservoir
The most important factor are:
a) Location of the dam
b) Run-off characteristics of the catchment area.
c) Water tightness of the proposed reservoir basin.
d) Reservoir rim stability.
e) Rate of sedimentation in the reservoir.
f) Water quality and
g) Seismic activity induced by the reservoir.

214
 Factors which influence the feasibility and economics of a
proposed reservoir site are:
Location of the dam

215
Reservoir
Run-off characteristics of the catchment area

Reservoirs problems:
watertightness- Seepage, Buried channels
216
Water
added
Leakage from
reservoir
Water
subtracted
-
Rainfall in
river basin
Infiltration
Evaporation
Transpiration
Net amount of water
available for storage
Runoff
-
1. Dam bypass
2. Water table effects

50 km
Ancient river/valley
Modern river/valley
Sautet
dam and
reservoir
Bypass of reservoir in drift
Reservoirs: leakage
217

before
after
water table divide
river
Leakage to next valley
reservoir
Bedrock with a water
table and finite
permeability
new
water
table
Reservoir problem: water table
leakage-1
218

before
Bedrock with low
permeability: aquiclude
High
layer
river
Water table in aquifer
reservoir
High
permeability
layer
Modified water table in aquifer
after
Leakage to next valley
Reservoirs: water table leakage-2
219

Before
Water table
river
reservoir
After - 1
Raised water table
reservoir
After - 2
Failure and
slumping
due to
weakened
rock mass
Reservoirs: raised water
table
220

221
Reservoir rim stability
Reservoir

222
Reservoir
Water quality(the effect of water and its contents) on
building materials, especially concrete)

223
Reservoir
Seismic activity induced by the reservoir
Present land use and social factors

Reservoir problem:
Sedimentation
224

Consequences of Reservoir Sedimentation
225
• Loss of Storage (yield; reliability)
• Upstream: loss of navigable depths
• Downstream: degradation of channel; loss of land and habitats
• Hydropower: downstream deposits can increase and decrease
efficiency HP
• Abrasion of turbines

How do we control sedimentation??
226
1. Reduce sediment inflow
erosion control and upstream sediment trapping.
2. Route sediments
Some or all of the inflowing sediment load may be hydraulically routed
beyond the storage pool by techniques such as off-stream reservoirs,
sediment bypass, and venting of turbid density currents.
3. Sediment removal
Deposited sediments may be periodically removed by hydraulic
flushing, hydraulic dredging, or dry excavation.
4. Provide large storage volume
Reservoir benefits may be considered sustainable if a storage volume
is provided that exceeds the volume of the sediment supply.

Spillway Design
227
Data needed to design spillways;
 Inflow Design Flood (IDF) hydrograph
- developed from probable maximum
precipitation or storms of certain
occurrence frequency.
 Reservoir storage
- storage volume vs. elevation
- developed from topographic maps
 Spillway discharge rating
 Perform hydraulic design of spillway
structures
- Control structure
- Discharge channel
- Entrance and outlet channels
 Selecting spillway type
Types of Spillway
 Overflow type – integral part
of the dam
i. Straight drop spillway
ii. Ogee spillway
 Channel type – isolated from
the dam
i. Side channel spillway, for
long crest
ii. Chute spillway – earth or
rock fill dam
iii. Drop inlet or morning glory
spillway
iv. Culvert spillway

Cont’d
228
39
Side Channel Spillway
Drop Spillway
Drop Chute
Ogee Spillway

Main causes of Dam Failure
229
(I) Failure of concrete dams
• Lack of shear strength and
discontinuity in foundation
• Excessive uplift in the foundation
(inadequate or non-existent drainage)
• Lack of dam stability
• Excessive or differential deformation
of the foundation
• Piping and erosion in the foundation
caused by high permeability
• Flaw in design
• Lack of supervision during
construction
• No monitoring or warning system
(systems were out of order)
 Human error during site
investigation, design,
construction and operation of
concrete dams:
 Inadequate foundation investigation
 Incomplete data on available
material
 Poor design
 Negligible construction supervision
 Incomplete first impoundment
 Incorrect operation of flood gates
 Insufficient monitoring and data
analysis
 Lack of preventive measures or
repair work

Main Causes of Dam Failure
230
(II) Failure mechanisms of Embankment Dam
Failure mechanisms are grouped into four general categories:
1. Slope stability,
2. Piping,
3. Overtopping and
4. Foundation failures
1. Slope stability failures
 For the rapid‐drawdown case, failure occurs on the upstream side of
the embankment as a result of a sudden lowering of the reservoir
level.
• For the seismic case, Liquefaction can occur during an earthquake in
loose, saturated, sandy soils.

231

232

233

234

Environmental impacts of
construction phase of dams
235
 River pollution
 Erosion
 Loss of aesthetic view
 Air pollution
 Noise pollution
 Dust
• Loss of land
• Habitat Destruction :
• Loss of archeological and histrorical
places
• Loss of mineral deposits
• Loss of special geological formations
• Aesthetic view reduction
• Sedimentation
• Change in river flow regime and flood
effects
• Reservoir induced seismicity effects
• Change in climate and plant species
ENVIRONMENTAL IMPACTS of RESERVOIRS

236
CHAPTER FIVE
Introduction to Engineering Geology of Tunnel
working

Tunnels
237
TUNNEL DESCRIPTION
1. Made into natural material (rocks)
2. Empty inside
3. Carry the loads itself
4. Both ends are open to atmosphere
5. Generally horizontal
6. Thick walled structure looks like
cylinder
Plates of the Tarmaber tunnel

238
1- Digging section
2- Support
3- Swelling section
4- Pressurized area
5- Flow direction of water
Tunnel Section for Swelling Ground

239
 There are 4 terms commonly used to
describe the location of the parts of
the tunnel cross section.
1) There is the floor, or invert.
2) The top of the cross section is the
roof, also referred to as back or
crown.
3) The sides of the tunnels are
referred to as tunnel walls, and
4) The spring line is the point where
the curved portion of the roof
intersects the top of the wall.

240
EXPLORATION & INVESTIGATIONS RELATED
to SLOPE STABILITY OF TUNNEL
 Geomorphologic mapping and preparation of longitudinal & cross
sections
 Geological mapping & surveying's (aerial photographs)
 Geophysical surveying
 Underground explorations, boreholes
 Ground water surveying
 Laboratory tests
 Model studies

241
SUBSURFACE EXCAVATIONS
1. GEOLOGY
a) Soil profile or hard rock geology
b) Structure
c) Ground water (hydrogeology)
d) Stability
2. INVESTIGATIONS
a) Mapping (Topographic, geologic, etc...)
b) Geophysical surveying (especially seismic velocity of rocks)
c) Test pits& boreholes
d) General and local stability analysis
e) Decide excavation method

242
FACTORS EFFECTING EXCAVATION of ROCKS
 Mineralogical composition of rocks
 Texture & fabric
 Petrographic features
 Structure
 Rock mass
 Strike & dip of beds in relation to face of excavation
 Intensity of tectonic disturbances
 Degree of weathering

Classification of tunnels
243
Tunnels can be classified according to their position or alignment and purpose.
Based on position and alignment four types of tunnels can be identified.
1) Saddle and base tunnels: constructed at the base of mountains and takes longer
distance (for railways).
2) Spiral tunnels
3) Off spur tunnels: used to shortcut minor local extruding obstacles
4) Slope tunnels: ensure safe operation and protection to railway and highway
routes in steep mountain hangs
Tunnel can be classified into four types depending on it’s purpose;;
i. Traffic tunnel is a tunnel that constructed underground for the passage
of roads and railways
ii. Hydropower tunnel is used to pass water under pressure and produce
power by colliding with generators.
iii. Public utility tunnels: this is relatively small and construct for carrying
utility lines for routing power, pipeline and telecom cables.
iv. Diversion tunnel: this tunnel is used for flood control or supplying
water for different purpose

244
 Classification of rocks for engineering purposes is needed in analyzing
the project costs and to obtain an economic and reliable solution.
 The classification of the rocks, that the tunnel will be constructed in, is
first done by Terzaghi. But, it is too general and gives qualitative
results.

245
Rock Tunneling Quality Index (Q) or NGI-Q

246
Tunnel support
1. Ground improvement ahead of the tunnel face
Injection of cement milk into the ground
Freezing of the water saturated ground
Drainage of water out of the area to be tunneled
2. Support during excavation
Shield (support) tunneling in soft ground
Bentonite tunneling with boring machine
Caisson tunneling to counteract (protect) water pressure
With shotcrete (sprayed grout) on the tunnel face and freshly excavated tunnel
sides
3. Support after excavation
Bolts
Anchors
Steel ribs
Shotcrete
Wire mesh or steel mats
Preformed concrete and backfill mortar
Formed concrete

Tunnels in different geological formations
247
I. Tunnels in soft ground
 These materials consist of gravels, sands, silts, clays and soft
shale's. They may be dry or water bearing.
 Excavation through such a ground does not require blasting.
Arch supports are always necessary. The soft ground may be
raveling, running or squeezing.
 In shallow tunnels that are driven in the soft ground, the roof
load is enormous. strong lining is required to support it.
II. Tunnels in rocks
 Tunneling through rocks requires blasting.
 If the rocks are structurally poor, support is often placed under
the tunnel ceiling to prevent the rocks from falling during
blasting.

248
The geological factors which influence tunneling are as
follows.
1) Swelling rocks
 If a tunnel is to be constructed through swelling rocks, it will
require special treatment. The examples of swelling rocks are
shale, unconsolidated tuff and anhydrite.
2) Inclined strata - In inclined rock beds when a tunnel is
driven parallel to the strike direction, there is a tendency
in the rocks to fall into the tunnel from the side where the
beds dip into the tunnel.
 This is particularly the case if the hard and soft rocks, such as
sandstone and shale are interbedded. When a tunnel is made
across the strike of rocks, it will traverse beds of different rocks.

249
Tunnel excavations in the slopes
3) Folded rocks - tunnels that are driven through synclinal folds joint
blocks form inverted keystones in the arch and cause rock falls.
In case the rocks happen to be water-bearing, the water flows into the tunnel and
causes great difficulties
Tunnel along the axis of a syncline and an anticline
 The discontinuities (layers, fissures) inclined
inside or outside of the slope are very important
regarding the stress and strength of the tunnel.
 Horizontal, vertical and inclined layers have
different kinds of loading conditions for tunnels

250
4) Fault zones - Faults are commonly found associated with a zone of highly
crushed rock or clay gouge. The crushed rocks being highly permeable allows
groundwater to seep into the tunnel. Besides this they also form unstable roof
rock.
5) Jointed rocks - Joints at one hand may help in excavating the rocks but on
the other hand they may present difficulties in tunneling.
6) Water-bearing rocks - Driving a tunnel though water-bearing rocks is a
difficult job. During excavation the groundwater rushes into the tunnel and
causes flooding.
Relation between the fault zone and the tunnel

Geological structures
251
(a) Dip and strike
• Influence tunnel excavation
• Three general cases
Unsafe condition
(I) Horizontal strata
Safe condition
 For small tunnels or for short lengths of
long tunnels, horizontally layered rocks
might be considered quite favorable but
 When horizontally bedded rock lies above
the roof, the thin strata near the opening
will tend to detach from the main rock mass
and form separated beams.

Geological…
252
(II) Moderately inclined strata (<45°)
• Tunnel axis parallel to dip
• Tunnel axis parallel to strike
Tunnel parallel to dip
Tunnel parallel to strike
When a tunnel is made across the strike of the rocks, it
will pass through different beds of rocks. In such cases,
there will be arching action or down ward pressure
from the roof. There is also the failure of incompetent
layers from the roof.
When a tunnel is driven parallel to the strike
direction, there is tendency in the rocks to slide
into the tunnel.

Geological…
253
(III) A) Steeply inclined strata (>45°)
• Tunnel axis parallel to dip
• Tunnel axis parallel to strike
Tunnel parallel to dip
Tunnel parallel to strike

Geological…
254
(b) Folded rocks
• Anticline fold
• Syncline fold

As a general the geological condition to be suitable for tunneling
should be;
– There should be one type of rocks
– There should be no faults and intrusion disturbance.
– The rocks should be soft but stiff enough not to need immediate
support near the face
– The rock should be impermeable and not adversely affected up on air
exposure.
– The rocks or the soil should not be changed its behavior under
the exposure to water (non- expandable)
– Not be highly weathered and resulted in collapse.

256
Tunnel construction/excavation methods:
 Mechanical drilling/cutting
 Cut-and-cover: constructed in shallow then covered over
 Drill and blast
 Shields tunnel method
 Tunnel boring machines (TBMs): without removing ground above
 Hard Rock Tunnel –mostly usedTBM
 Soft Ground Tunnel –Use Tunnel Shield

1. SHIELD TUNNELLING METHOD
257
 has protective structure used in the excavation of tunnels
through soil that is too soft or fluid to remain stable.
 Used mostly for deep tunnel
 the shield serves as a temporary support structure for the
tunnel while it is beingexcavated.
 This construction method causes minimal disruption to traffic
and the environment because all the work takes place below
ground and the ground level environment is unaffected.

2. CUT and COVER TUNNELLING METHOD
258
 Cut-and-cover is a simple method of construction for shallow tunnels
where a trench is excavated and roofed over with an overhead support
system strong enough to carry the load of what is to be built above the
tunnel.
 Two basic forms of cut-and-cover tunneling are available.
 Bottom-up method: A trench is excavated, with ground support as
necessary, and the tunnel is constructed in it.
 Top-down method: Side support walls and capping beams are
constructed from ground level.

3. TBM (Tunnel Boring Machine)
259
A. Mechanical-support TBM
B. Compressed-air TBM
C. Slurry shield TBM
D. Earth pressure balance machine

Soft Ground TBM
260

A- Mechanical Support TBM
261
 It has a full-face cutterhead which provides face support by
constantly pushing the excavated material ahead of the cutterhead
against the surrounding ground.
B- Compressed-Air TBM
 A compressed-air TBM can have either a full-face cutterhead or
excavating arms. Confinement is achieved by pressurizing the air
in the cutter chamber.
C- Slurry Shield TBM
 It has a full-face cutterhead. Confinement is achieved by
pressurizing boring fluid inside the cutterheadchamber.
 most suited for tunnels through unstable material subjected to
high groundwater pressure.

D - Earth Pressure Balance Machine
 It has a full-face cutterhead. Confinement is achieved by pressurizing
the excavated material in the cutterhead chamber.
 in which spoil is admitted into the TBM via a screw conveyor
arrangement which allows the pressure at the face of theTBM.
262
 The process for bored tunneling involves all or some of the
following operations:
Probe drilling (when needed)
Grouting (when needed)
Excavation (or blasting)
Supporting
Transportation of muck
Lining or coating/sealing
Draining
Ventilation Wollo University, Ethiopia Elias A.

263
CHAPTER SIX
ROADS, BRIDGES AND RAILWAYS

264
For rapid economic, industrial and cultural growth of any country a good system of
transportation is very essential
Transportation: good network of roads, railways, water ways, and airways.
As blood circulation through body arteries is essential for well being of a human being,
similarly a good system of transportation is essential for well being of a nation.
ROADS, BRIDGES AND RAILWAYS
Roads
Highway or road engineering: covers designing, maintenance & operation of the
roads for the convenience of the road traffic.
Out of all types of transport systems road is nearest to man.
Highway/ Road Planning
Planning of roads/ highways is done to
1. Provide a most suitable type of road, of maximum length with the available
funds.
2. Plan road system for future anticipated requirements
3. Funds Vs. required road system (phased programme for road development)
4. Planning helps fix priorities of roads
5. Planning is also helpful to work out financing system of roads.

265

ROAD CLASSIFICATION
266
 Roads can be classified according to traffic volume, tonnage, location and function they have
to perform.
 According to traffic volume: heavy, medium, light traffic roads
 Nagpur Conference (1943) Plan classification according to location and function of the
roads.
1. National Highway (NH)
2. State Highway (SH)
3. District roads
I. Major district roads (MDR)
II. Other district roads (ODR)
4. Village roads
 Engineering Studies of roads: include studies like
1. Topographical survey of area
2. Soil survey of the area
3. Existing facilities of roads and railways
4. Anticipated development due to introduction of proposed high way
5. Road life studies
6. Specific problems in construction, maintenance & drainage of roads.
7. Availability of labour & materials for the construction of the roads
– Details collected in the studies are tabulated & plotted on the maps of the area
under planning.

Factors which control the selection of alignment for new road route
1. Volume & type of traffic expected to use the road
2. Obligatory points to be touched & not to be touched by road
3. Topographical features of the area through which road has to
traverse.
4. Geometrical standards to be adopted
5. Canal, river or railway crossings
6. Flood in the area
7. Geological conditions
8. Places of availability of construction materials and labour.
9. Existing right of way
10. Avoiding road passing through a village or town.
11. Political and other considerations
267

268
Topographical features of the area
 Every effort should be made to achieve easy gradients, large
radius horizontal curves.
 As far as possible road should run on the ridge
 It avoids heavy expenditure on cross-drainage works
 Road alignment parallel to the land drainage is cheaper than across it.
Canal, river or railway crossings
 Crossings of river, canal etc. is considered best at right angle.
 Road alignment may be deviated so as to cross these features at
right angles.
 Bridge site on river is selected considering the structural and
foundation requirements

•Geological conditions
• Geological condition of the area should be thoroughly investigated
• To locate road alignment on good soil & good foundation conditions for
proposed cross drainage
• Good soil will not easily promote subsidence of road, & will not easily slide or
slip at the slopes
• Marshy and water logged lands should be avoided : difficulty to construct and
maintain a road in such places.
• Cuttings and fillings in rocky soils are expensive and generally not good.
• Availability of construction materials and labour.
• Road alignment should pass through such places where labour & good
construction materials are easily available.
• Avoiding road passing a village or town.
• Road alignment : pass by the side of a village or town
• This is to avoid unnecessary traffic congestion on local internal roads and
possible accidents.
269

STEPS IN NEW HIGHWAY PROJECT
• Various steps in the construction of new road project are
summarized as follows.
1. Survey work: map survey, location survey, etc.
2. Materials: soils at sub-grade are tested & classified, aggregates
to be used tested, located
3. Design work: pavement & cross-drainage works, etc. are
designed according to the requirements, slopes of cut and
embankment are fixed based on soil type (see table), depth of
cut & height of embankment
4. Earth work: cuttings and fillings done, compaction at optimum
moisture content
5. Pavement Construction: preparation of sub-grade & laying of
sub-base, base, & surfacing layer
6. Construction control: Proper quality control of construction at
different stages, finished surfaces are checked for unevenness,
in-situ density test, etc.
270

271
S. No. Types of stratum Slope (V : H)
1 Hard sound rocks Vertical or nearly
vertical
2 Medium rock 12:1 to 16:1
3 Soft rock 8:1 to 16:1
4 Disintegrated loss
rock or conglomerate
2:1 to 4:1
5 Hard clay 1:1 to 1:11/2
6 Ordinary soils 1:11/2 to 1:2

272

273

274

275

276

277

• Soil Classification Systems in Highway/Road
1. Rough classification: coarse & fine grained.
2. Grain size classification: gravel, sand, silt, clay
3. Textural classification: clay, clay loam, silty loam, etc.
4. AASHTO Classification system
5. Unified Soil Classification system
278
Pavements
Pavements are of basically three types;
i) Flexible Pavement
ii) Rigid Pavement
iii) Semi Flexible Pavement
Semi Flexible Pavement
A semi flexible pavement has flexural rigidity in between that of a rigid pavement and
a flexible pavement. Such pavements are usually made of pozzolanic concrete, lean
concrete or soil cement in the base course or sub-base.
As the flexural strength of such layers is limited the pavement can resist only moderate
tensile stresses.

279

280

281

282
Typical stress distribution under a flexible and a rigid pavement

283

284
Cross-section exhibiting heave under flexible pavement- Addis Ababa-Jima
Road (km 13-14)

285
Rigid and Flexible Pavement Characteristics
 Primary difference is the manner in which the pavements distribute traffic loads
over the subgrade.
• A rigid pavement has a very high stiffness and distributes loads over a relatively
wide area of subgrade
-the structural capacity is mainly on the slab itself
• The load carrying a capacity of a flexible pavement is derived from the load-
distributing characteristics of a layered system
Materials Investigation and Selection Information
Material selection forms one of the three legs of the high performing pavement

BRIDGE
• Bridges are the civil engineering structures which are constructed to provide
access across the natural or manmade obstacles. A bridge consists of a super-
structure and a substructure.
 Canal, river crossings
 Crossings of river, canal etc. is considered best at right angle.
 Road alignment may be deviated so as to cross these features at right angles.
 Bridge site on river is selected considering the structural and foundation
requirements
 Problem in the channel section is to determine the depth of unsuitable material to
be removed.
 Drilling and geophysical methods are employed
 Buried channels
 Stable abutments or Banks
 A river valley should always be suspected of concealing a fault
 To locate faults and other unsuitable materials on a proposed bridge drilling of
oblique (at angle) holes proves the most effective method
286

287
Stability of bridges
 The chief factors which govern the stability of bridges are lateral forces,
earthquake forces, and scouring action of rivers.
Foundation of bridges
 The weight of the bridge, the load of the traffic and pressure of the wind and
flowing water are ultimately transmitted to the foundation of the piers and
abutments.
 Therefore the design and construction of bridges is governed largely by the nature
of rocks, structure of rocks, faults, and type of river channel.

288

289
a. Beam bridges
b. Cantilever bridges
b. A cantilever bridge is a
bridge built using
cantilevers: structures that
project horizontally into
space, supported on only
one end.

290
 c. Arch. The arch is squeezed together, and this
squeezing force is carried outward along the curve to
the supports at each end. The supports, called
abutments, push back on the arch and prevent the
ends of the arch from spreading apart.
Arch bridges

291
d. Suspension Bridges
This kind of bridges can span 600m to
2000m-- way farther than any
other type of bridge! Most suspension
bridges have a truss system beneath the
roadway to resist bending and twisting.
e. Cable-stayed bridges
• The cable stayed bridge is
newer than the other types
of bridge.
• Large upright steel
supports are used to
transmit the load into the
ground.
Cable-stayed bridges
Suspension Bridges

292
f. Truss Bridge
 All beams in a truss bridge are
straight. Trusses are comprised
of many small beams that
together can support a large
amount of weight and span
great distances.
g. Floating Bridge
 Permanent floating bridges are useful for
traversing features lacking strong bedrock for
traditional piers.

Railways
293
 Railroads have played and continue to play an important role in
national transportation systems, although the construction of new
railroads on a large scale is something that belongs to the past.
 Railroads continue to be built such as those associated with high-speed
networks.
 A vital part of a high-speed railroad, with trains travelling at speeds of
up to 300 km/h, is the track bed support.
 In other words, the dynamic behavior of foundations and earthworks
involves a detailed understanding of the soil–structure interaction.
This distinguishes a modern high-speed railway from other railways or
highways.
 Obviously, the grades and curvature of railroads impose stricter limits
than do those associated with highways.

294

295
 Railway track formations normally consist of a layer of coarse
aggregate, the ballast, in which the sleepers are embedded.
 The ballast may rest directly on the sub grade or, depending on the
bearing capacity, on a layer of blanketing sand.
 The function of the ballast is to provide a free-draining base that is
stable enough to maintain the track alignment with the minimum of
maintenance.
 The blanketing sand provides a filter that prevents the migration of
fines from the sub grade into the ballast due to pumping.
 The ballast must be thick enough to retain the track in position and to
prevent intermittent loading from deforming the sub grade, and the
aggregate beneath the sleepers must be able to resist abrasion and
attrition.
 The thickness of the ballast can vary from as low as 150 mm for
lightly trafficked railroads up to 500 mm on railroads that carry
high-speed trains or heavy traffic.
 The blanketing layer of sand normally has a minimum thickness of 150
mm. Wollo University, Ethiopia Elias A.

296
1
CHAPTER SEVEN
GEOLOGICAL CONSTRUCTION MATERIALS

Introduction
297
2
 Many civil & hydraulic structures require various construction materials with
good quality and quantity.
 Construction materials are extremely variable in terms of their type and
intended use.
 The following are important questions/points:
 Is the material produced locally?
 Is it cheap, abundantly available?
 Is the material & construction climatically accepted?
 Can the material and technology be used and understood by local workers, or
special skills and experience required?
 Does it require special machines, transportation?, etc.
 At present day the construction industry places a large demand upon rock & soil
products in the form of natural stone for dressing & foraggregates,
 clay for bricks & embankment,
 limestone for cement &
 gypsum for plaster.
 And many rock types for riprap and masonry stone.

298
 Quarry: is place where rock is separated from its natural beds
and processed for use in construction. Quarrying is the process
of breaking and obtaining stones from their natural rock out
crops.
Types of quarries
There are two types of quarries:
Open and under ground quarries.
 Open quarries may be shelf quarries, where the rock is
extracted from hillside, or pit quarries,
 underground quarries are those in which the rock is extracted
from a certain depth in the ground.
 Quarry products are dimension stone, crushed stone, and broken
stone (riprap).

299
The controlling factor for selection of quarry site:
 The search of rock material for building stone, crushed
rock, or riprap is controlled by factors
(1) quality
(2) supply of the material (quantity) and
(3) economics of production and delivery
Quarrying methods
 Quarrying is done by one of the following 4 methods after
investigation of its quality, quantity and economic benefit.
i) Excavating
ii) Wedging
iii) Heating
iv) Blasting.

300
I. Excavating: This method is employed when stones to be quarried are
lying buried in earth or are under loose overburden before excavating.
Cut and grade the access road to the sit
Cut an access road to the area, which will become the head, or top, of the
quarry face.
Carry out the initial leveling and grading of the area.
Remove at least sufficient over burden to allow an early start on developing
the largest practicable rock face.
 After these arrangements Shovels, Pick. Axes, Hammers and Chisels etc. are
made ready to use in the excavation work.
II. Wedging: This method is suitable for quarrying soft stratified rocks.
The operation is started near a vertical face. In this method steel
wedge is hammered in to the rock to create cracks into which steel
bars are inserted and the stone blocks are separated.
If vertical face is absent, cutting or boring channel or drilled holes create a
vertical face by power drilling machines. To separate big blocks of proper
dimensions, lifting crane, plugs, steel hammers (sledgehammers) are used in
drilled holes.

301
III. Heating: This method is suitable where only small blocks of more or less regular
shape are required and suitable rocks bedded in horizontal layers, which have not
much thickness to be quarried.
This method consists of filing a heap of fuel on small area of the exposed rock face and
burning a steady fire for some hours. Because of uneven heating to top and bottom
layers, the rock masses separate themselves along the joint with some sound.
IV. Blasting: It is the quarrying of stones using explosives. The purpose of blasting
for the quarrying is to loosen large masses of rocks and not to violently blowup the
whole rock mass into pieces.
Quarrying by blasting requires the following steps:
Drilling of blast holes of calculated dimensions at predetermined places in the rock.
These drilled holes are charged with the explosives of suitable quality in a carefully
selected manner.
Igniting or firing of charge or shot, which explode with in the body of the rock and
thus rocks, break in to parts and thrown into at distances that depend upon the quantity
and quality of the explosives used in the shot.

302
The two basic kinds of explosives are black blasting powder and high explosives.
1.Black blasting powder: is used in dimension stone quarries. Black blasting powder
may be either “A” blasting powder or “B” blasting powder type.
“A” blasting powder that is mixture of charcoal, potassium nitrate, and sulfur in
proportion of about 15:75:10 respectively.
“B” blasting powder that is mixture of charcoal, sodium nitrate, and sulfur in
proportion of about 16:72:12 respectively. “B” blasting powder is slower and less
expensive than “A”
2. High explosives: are used in crushed stone quarries and in most civil engineering
excavation operations. High explosive may be:
Those containing mainly Nitroglycerin and Nitroglycol both are designated by
symbol NG. These are the main types used in civil engineering.
They commonly referred as dynamite, and they may have either a granular or
gelatinous nature. Nitroglycol is less expensive than Nitroglycerin.
Those, which do not contain NG-types (mostly military type explosives). Dynamite
should not explode by detonation.
Blasting powder or Gunpowder can be ignited by means of fuse.

303
Properties of Building Stones
 The properties that are commonly examined for rock materials, which used for
construction, are:
Mineral composition
Texture
Structure
Porosity
Permeability
Durability
Strength of rock
Resistance to fire
Common Types of Building Stones and their Uses
 Building materials (stones) are products of rocks that are used in
construction of buildings, dams, bridges, retaining structure etc.
 The rock materials used for construction include:
Building stones in the form of masonry blocks
Rubble-in the form of small irregular fragments
Crushed stones-to make concrete
Limestone-to make lime and cement

Aggregate
304
13
 Crushed or natural materials derived from the natural sources such as
rocks, gravel, boulders and sand for production of concrete.
 There are two types of aggregates:
 Fine aggregates are particles <5mm and 90-100% which passes through
4.75 mm sieve, while coarse aggregate is particles which retained on
4.75 mm sieve.
 In general aggregate should be:
 Chemically inert, strong, hard, durable, of limited porosity,
 Free from adherent coatings, clays and organic matter
 Other admixtures that may cause corrosion of the reinforcement or
impair the strength or durability of the concrete.
 Determination of the quality and quantity of aggregates available to the
project is highly imperative.

 Aggregates used in roads and runways are subjected to constant wear due to
friction.
 In addition to good strength, the aggregate must have good wear
resistance.
 Soundness of an aggregate is another important characteristics to be
considered. B/c aggregates disintegrate into smaller particles when
exposed to changes in temperature and variable weather, it should be
sound.
 The soundness of an aggregate is measured by subjecting it to alternate
wetting in saturated solution of sodium or magnesium sulfate and drying it
in oven through a set of cycles.
 Structures made of good quality aggregates measured by strength,
rigidity and water-tightness, and resistance to wear, weather and other
destructive agents.
14
305

 Aggregates containing silt and clay particles in excess of 2% by
weight should not be used.
 Aggregates with specific gravity below 2.4 are usually suspected of
being potentially unsound, b/c of poor quality.
 High absorption in aggregates may be an indication of potential
high shrinkage in concrete and may need further investigation.
 Excessive amounts of flat or elongated particles, in aggregates will
severely affect the water demand and finishability.
 In mass concrete structures, the amount of flat or elongated
particles, 3:l (length-to-width) is limited to 25% in any size group of
coarse aggregate.
 Water for curing must not contain harmful chemical
concentrations and must not contain organic materials such as
iron compounds which will cause staining.
15
306

307
Quality
Rock quality is determined by laboratory & field testing,
Selection of the samples for testing are critical in determining the
material quality.
Right selection of materials can be made for a construction activity only
when material properties are fully understood.
Some of the most important properties of building materials are grouped
as follows.
Group Properties
Physical Shape, Size, Density, Specific Gravity etc.,
Mechanical
Strength, Elasticity, Plasticity, Hardness, Toughness, Ductility,
Brittleness, Creep, Stiffness, Fatigue, Impact Strength etc.,
Thermal Thermal conductivity, Thermal resistivity, Thermal capacity etc.,
Chemical Corrosion resistance, Chemical composition, Acidity, Alkalinity etc.,
Optical Color, Light reflection, Light transmission etc.,
Acoustical Sound absorption, Transmission and Reflection.
Physiochemical Hygroscopicity, Shrinkage and Swell due to moisture changes

308
Definitions
Density: It is defined as mass per unit volume. It is expressed as kg/m3.
Specific gravity: It is the ratio of density of a material to density of water.
Porosity: The term porosity is used to indicate the degree by which the
volume of a material is occupied by pores. It is expressed as a ratio of
volume of pores to that of the specimen.
Strength: Strength of a material has been defined as its ability to resist the
action of an external force without breaking.
Elasticity: It is the property of a material which enables it to regain its
original shape and size after the removal of external load.
Plasticity: It is the property of the material which enables the formation of
permanent deformation.
Hardness: It is the property of the material which enables it to resist
abrasion, indentation, machining and scratching.
Ductility: It is the property of a material which enables it to be drawn out or
elongated to an appreciable extent before rupture occurs.
Creep: It is the property of the material which enables it under constant load
to deform slowly but progressively over a certain period.

309
Brittleness: It is the property of a material, which is opposite to ductility.
Material, having very little property of deformation, either elastic or plastic is
called Brittle.
Stiffness: It is the property of a material which enables it to resist deformation.
Fatigue: The term fatigue is generally referred to the effect of cyclically
repeated stress. A material has a tendency to fail at lesser stress level when
subjected to repeated loading.
Impact strength: The impact strength of a material is the quantity of work
required to cause its failure per its unit volume. It thus indicates the toughness of
a material.
Toughness: It is the property of a material which enables it to be twisted, bent
or stretched under a high stress before rupture.
Thermal Conductivity: It is the property of a material which allows conduction
of heat through its body. It is defined as the amount of heat in kilocalories that
will flow through unit area of the material with unit thickness in unit time when
difference of temperature on its faces is also unity.
Corrosion Resistance: It is the property of a material to withstand the action of
acids, alkalis gases etc., which tend to corrode (or oxidize).

310
Quantity
Estimating realistic quantities depends on:
an understanding of subsurface geologic conditions.
The uniformity of rock and discontinuities within a source
area
This estimate (often referred to as the reserve) provides
not only the amount available but also provides an
understanding of wastage resulting from blasting,
handling, processing, haulage, and placement..

Riprap & masonry stone
311
16

Riprap
312
Riprap is preferably a relatively thin layer of:
 Large, approximately equidimensional,
 Durable rock fragments or blocks placed on bedding
 To dissipate water energy and protect a slope, channel bank or shore
from erosion caused by the action of runoff, currents, waves or ice
17

 Riprap surfaces on earth dams must:
 withstand severe ice and wave action
 withstand heavy rainfall, turbulent flow
 as well as destructive forces associated with temperature
changes, which includes freezing and thawing, heating and
cooling, and wetting and drying.
 Riprap either: dry-dumped or hand-placed, concrete pavement, steel
facing, bituminous pavement, precast concrete blocks, soil-cement
pavement, wood & sacked concrete.
 Riprap should be “hand” placed to reduce the void space and
maximize the interlocking arrangement, but rarely is this
economical
18
313

 Most riprap is dumped and falls into place by gravity with little or
no additional adjustment.
19
314

Riprap Quality
315
20
 Rock quality is determined by laboratory & field testing.
 There are numerous quarries and pits capable of producing aggregate,
but not all sources are suitable for the production of riprap.
 Riprap sources must produce:
 the necessary weight & size,
 shape,
 gradation, &
 durability to be processed and placed and then remain “nested” for the
life of the project.
• Performance on existing structures is a valuable method of assessing
riprap quality from a particular source.

Shape of riprap
316
21
The shape of individual rock fragments affects the workability and
nesting of the rock assemblage.
 Natural “stones” from alluvial and glacial deposits are usually rounded to
sub-rounded and are easier to obtain, handle, and place and, therefore, are
more workable.
 Rounded stones are less resistant to movement. b/c the stones interlock
more poorly than angular rock fragments, easily eroded by water action.
 Angular-shaped rocks nested together resist movement by water and
make the best riprap.
 The rock fragments should have sharp, angular, clean edges at the
intersections of relatively flat faces.
 Alluvial deposits are used as riprap sources only if rock quarries are
unavailable, too distant, or incapable of producing the appropriate sizes.
 Rounded to sub-rounded stones are typically used only on the
downstream face of embankments, in underlying filters, or as the
packing material in gabions.

• Most igneous and some sedimentary rocks are capable of making
suitably shaped fragments. However, secondary fracturing or
shearing will affect the shape.
• Rocks having closely spaced discontinuities tend to produce
fragments that are too small.
• Sedimentary rocks that have bedding plane partings tend to produce
flat shapes.
• Metamorphic rocks tend to break along jointing, rock cleavage, or
mineral banding and often produce elongated shapes.
23
317

Weight and Size
318
24
 The weight and size may be determined in the laboratory or in the field
 The unit weight of riprap generally varies from (2.4 to 2.8 g/cm3)
 Rock having unit weight above 2.6 g/cm3 is typically suitable for riprap.
 Most rock sources are capable of producing suitable weights and sizes.
 The size rarely impacts use as a riprap source unless more than 30% of
the rocks are elongated or flat.
 Size range is controlled by discontinuities in the rock.
 Columnar basalt, some fine-grained sedimentary rock, and metamorphic
rock commonly have inherent planes of weakness that limit larger riprap
sizes.
 the rock mineralogy and porosity also controls the weight of riprap.
 Generally, rock having a low unit weight is weak and tends to break.

Gradation
319
25
 The desired size fractions of the individual particles that will nest
together and withstand environmental conditions.
 The gradation design is based on the ability of the source(s) to produce
appropriate sizes.
 Most coarse-grained sedimentary and igneous rock quarries are
capable of producing suitable riprap gradations.
 Intensely to moderately fractured rock rarely produces suitable riprap
gradations.

Durability
320
 Riprap durability affects the ability of a source to provide a consistent
shape, size, and gradation and the ability to resist weathering and
other environmental influences.
 Durability is a function of the rock’s mineralogy, porosity, weathering,
discontinuities, and site conditions. In rare instances, environmental
considerations such as Abnormal pH of the water may be a controlling
factor in selecting an appropriate riprap source.
26

Quantity
321
27
 Every riprap source must provide the estimated quantity required.
Estimating realistic quantities depends on: understanding of
subsurface geologic conditions, uniformity of rock and discontinuities
within a source area.
This estimate (often referred to as the reserve) provides not only the
amount of riprap available but also provides an understanding of
wastage resulting from blasting, handling, processing, haulage, and
placement..

28
322

Masonry Materials or Building or DimensionStone
323
29
 A number of factors determine whether a rock will be worked
as a building stone. These include
 the volume of material that can be quarried,
 the ease of quarry site,
 the wastage consequent upon quarrying and,
 the cost of transportation; as well as its appearance and physical
properties
 Stone (rock) suitable for structures should be:
 Hard and durable.
 Available in blocks of sufficient size to form the elements of the
structure.
 Of suitable texture for shaping as required.

30
324

31
325

326
CHAPTER EIGHT
FOUNDATION GEOLOGY

Major Building Parts
Substructure
Foundation
Superstructure

Introduction to foundation
328
• What is a foundation?
■ “The foundation of a building is that part of walls, piers and columns
in direct contact with the ground and transmitting loads to the
ground.”
■ Every building needs a foundation of some kind.
■ Because of the variety of soil, rock, and water conditions that are
encountered below the surface of the ground and the unique demands
that buildings make upon their foundations, foundation design is
a highly specialized field combining aspects of geotechnical and
civil engineering.

Purpose of foundation
■ To distribute the load of the structure over a large bearing area so as
to bring the intensity of load within the safe bearing capacity of soil.
■ To load the bearing surface at a uniform rate to avoid differential
settlement.
■ To prevent the lateral movement of supporting material.
■ To attain a level and firm bed for building operations.
■ To increase the stability of the structure as a whole.
 Foundations must be designed to maintain soil pressures at all depths
within the allowable bearing capacity of the soil and also must limit
total and differential movements within levels that can be tolerated by
the structure.

Types of foundation
■ There are two basic types of foundations
1. Shallow foundation- Df /B≤ 1
2. Deep foundation- Df /B≥ 15
According to Terzaghi’s (1943)

331
Shallow foundations in soils are required when the magnitude of loads to be
transmitted to the foundation soil is relatively small and the soils at the shallow depth
possess relatively satisfactory bearing capacity.
Types of Shallow Foundation
1. Strip footing/
continuous footing
A strip footing is provided for a load-bearing wall. A strip footing is
also provided for a row of columns, which are so closely spaced that
their spread footings overlap or nearly touch each other.

2. Spread footing (single or isolated footings)
332
A footing carrying a single column is called a spread footing, since it’s function is to
“spread” the column load laterally to the soil so that the stress intensity is reduced to
a value that the soil can safely carry.
As the term itself indicates, a spread
footing takes up the weight of a Spread
Footing part of the building and spreads
it over a larger area in order to decrease
the unit load.

3. Mat foundations
333
A mat or raft foundations is a large slab supporting a number of columns and walls
under the entire structure or Combined footing a large part of the structure. Or it’s a large
concrete slab used to interface one or more columns in several lines with the base soil.
A mat foundation may be used
where the base soil has a low
bearing capacity and/or the loads are
so large that more than 50 percent of
the area is covered by conventional
spreading footings.
Mat foundations

334
4. Combined footings: similar to spread footings but support
two or more columns.
– Shape: rectangular or trapezoidal.
– used where column spacing is non-uniform and for the
support of exterior columns.
Combined footing
Advantages of SF
1. Cost (affordable)
2. Construction Procedure (simple)
3. Materials (mostly concrete)
4. Labor (does not need expertise)
Disadvantage of SF
1. Settlement
2. Limit Capacity * Soil * Structure
3. Irregular ground surface (slope,
retaining wall)

Deep foundations
335
Deep foundations are analogous to spread footings but distribute the load vertically rather
than horizontally.
Piles are driven to carry loads down to satisfactory bearing layer.
1. Pile Foundation
Pile foundations are used in the following conditions:
I. When the strata at or just below the ground surface is highly compressible and very weak
to support the load transmitted by the structure.
II. When the plan of the structure is irregular relative to it’s outline and distribution. It would
cause non-uniform settlement if a shallow foundation were constructed. A pile foundation
is required to reduce differential settlement.
III. Pile foundations are required for the transmission of the structural loads through deep water
to a firm stratum.
IV. Pile foundations are used to resist horizontal forces in addition to support the vertical loads
in earth-retaining structures and tall structures that are subjected to horizontal forces due to
wind and earthquake.
V. Piles are required when the soil conditions are such that a wash out, erosion or scour of soil
may occur from underneath a shallow foundation. Piles are used for the foundations of
some structures, such as transmission towers, offshore platforms, which are subjected to
uplifts.

336
(vii) In case of expansive soils, such as black cotton soils, which swell or shrink as the water content
changes, piles are used to transfer the load below the active zone.
(viii) Collapsible soils, such as loess, have a breakdown of structure accompanied by a sudden
decrease in void ratio when there is an increase in water content. Piles are used to transfer the load
beyond the zone of possible moisture changes in such soils.

337
2. Drilled Pier and Caisson
Drilled Piers
 A drilled pier is a large diameter concrete
cylinder built in the ground.
 For construction of a drilled pier a large
diameter hole is drilled in the ground and later
it is filled with concrete.
 A drilled pier is a type of deep foundation
constructed to transfer heavy axial loads to a
deep stratum below the ground.
 The transfer of load to the soil from a drilled
pier can take place through end bearing or
through skin friction or a combination of both.

DESIGN PARAMETERS
Design parameters for shallow foundations: structural and
geotechnical design parameters
• Structural design
parameters
– Building types and use
– Loading (live, dead and
uplift)
– Column spacing
– Presence or absence of
basement
– Allowable settlement
– Applicable building codes
• Geotechnical Design
Parameters
– Thickness & lateral extent of
bearing strata
– Depth of frost penetration
– Depth of seasonal volume
change
– Cut/fill requirements
– Strength
– Compressibility
– Shrink and swell potential of
the bearing strata
– Presence or absence of GW
and its max. & min. Elevations.
338

BEARING CAPACITY OF SHALLOW FOUNDATIONS
339
• The foundation should be designed such that
a) The soil below does not fail in shear &
b) Settlement is within the safe limits.
• General Considerations
– In temperate latitudes footings are commonly located at a depth
not less than that of normal frost penetration
– In warmer climates and in semiarid regions
• The minimum depth of footings may be governed by the greatest
depth at which seasonal changes in moisture cause appreciable
shrinkage & swelling of the soil.
– The elevation at which a footing is established depends on
• The character of the subsoil
• The load to be supported, &
• The cost of the foundation.
12

• Normally the footing is located at the highest level where
adequate supporting material is found.
• The excavation for a reinforced concrete footing should be
kept dry.
• In water-bearing soil it may be necessary to pump either
from sumps or from a previously installed system of drains, if
present
340

Bearing Capacity
341
• BC is the maximum soil capacity to resist the load.
• There are two major type of failure, as follows:
– Shear Failure, the shear stress is exceed the soil shear strength.
Terzaghi call this failure stability problem.
– Settlement Failure, the normal stress induced the soil to settle
excessively. Terzaghi call this failure elasticity problem
• Due to the type of failure above the geotechnical engineer must
investigate both the shear resistance and settlement of the soil
material.
– This investigation is called bearing capacity analysis.
• The allowable bearing capacity used in the design must consider the
minimum:
– Limiting the foundation settlement.
– Limiting bearing capacity
• The bearing capacity is can be calculated based on the soil
properties and also based on the in situ test result.

• Bearing pressure is defined as the pressure at the
interface between soil and the foundation.
• The type of bearing pressure beneath the foundation is
depend on the rigidity of the foundation.
• The flexible foundation produce uniform bearing pressure
and rigid foundation produce non-uniform pressure
342

• Bearing Capacity: There are two types of bearing
capacity:
– Ultimate Bearing Capacity: the theoretical maximum
pressure which can support without failure
– Allowable Bearing Capacity, design bearing capacity
based on the several factors such type of soil, type of
foundation, risk etc.
– Allowable bearing capacity is design bearing capacity permitted
used in the design.
– (qa = (qult*FS)
where : qa = allowable bearing capacity, qult= ultimate
bearing capacity
FS = factor of safety
343

ANALYSIS OF BEARING CAPACITY
344
• Several geotechnical engineers already proposed the bearing
capacity formula such as:
– Terzaghi,
– Meyerhof,
– Brinch Hansen and
– Vesic, etc.
• Each formula has different assumption. During the usage of
the bearing capacity formula we must know the basic
assumption used when the formula is derived.

TERZAGHI’S METHOD
345
The followings are the basic assumption used in the Terzaghi
theory of bearing capacity, as follows :
• Depth of foundation Df≤ B, B = width of foundation.
• No sliding between foundation and the soil.
• The soil material is homogeneous.
• The failure is govern by general shear failure.
• No soil consolidation.
• Foundation is rigid compared to the soil.

• General Shear Failure
– The bearing capacity of continuous footing when the general
shear failure governs is :
qult= CNcsc + DfNq +0.5BNs
where:
qult = ultimate bearingcapacity
C = cohesion of soil
 = unit weight of soil
Df = equivalent surcharge
sc,s = shapefactor
Nc,Nq,N = Terzaghi bearing capacityfactor
346

347

• Local Shear Failure
– The bearing capacity of continuous footing when the
local shear failure governs is
qult= CN’cs’c + DfN’q +0.5BN’s’
348

SETTLEMENT OF FOOTINGS
349
• When a soil layer is subjected to a compressive stress, such as
during the construction of a structure (FOOTING), it will
exhibit a certain amount of settlement/compression.
• This compression/settlement is achieved through a number of
ways, including
– rearrangement of the soil solids or
– Compression of water and air within the voids or
– extrusion of the pore air and/or water.
• According to Terzaghi (1943), “a decrease of water
content of a saturated soil without replacement of the
water by air is called a process of consolidation.”

350
CHAPTER NINE
Engineering geological mapping
 Maps, features and attributes of engineering geological
maps
 Methods and tools used in production of engineering
geological maps and cross sections

351
INTRODUCTION
 An engineering geological map is a type of geological map which
provides a generalized representation of all those components of a
geological environment of significance in land use planning, and in
design, construction and maintenance as applied to civil and
mining engineering.
 Engineering geological maps should be based on geological,
hydrogeological and geomorphological maps, but must present
and evaluate the basic facts provided by these maps in terms of
engineering geology.
 The purpose of engineering geological maps is to provide basic
information for the planning of land use and for the planning,
design, construction and maintenance of civil engineering works.

352
An engineering geological map should fulfill the
following requirements.
1) It should portray the objective information necessary to evaluate the
engineering geological features involved in regional planning, in the
selection of both a site and the most suitable method of construction, and in
mining.
2) It should make it possible to foresee the changes in the geological situation
likely to be brought about by a proposed undertaking and to suggest any
necessary preventive measures.
3) It should present information in such a way that it is easily understood by
professional users who may not be geologists.

353
 Engineering geological mapping is mainly directed towards
understanding:
 The interrelationships b/n the geological environment and the engineering
situation.
 The nature and relationships of the individual geological components
 The active geodynamic processes and
 The prognosis of processes likely to result from the changes being made
 The principal factors creating the engineering geological conditions
of an individual site or area are
 the rocks and soils,
 water,
 geomorphological conditions and
 geodynamic processes.

354

355

356
Engineering Geological Maps production requires
1. Location map
2. Engineering geological cross‐section
3. Single value maps.
– Single value maps are types of maps indicating and preparing
standardized interpretation of data about the depth and thickness of
layers in a soil profile
4. Multipurpose comprehensive maps.
– These maps only portray the soil profile, thickness, depth of individual
layers
5. Soil mechanical properties. The geotechnical, hydrogeological
and geochemical properties of different soil layers
6. Foundation depth and settlement maps
– special‐purpose maps such as settlement‐ depth maps, industrial
aggregate maps, hydrological maps and environmental geological
maps

357
Main Purpose Engineering Geological Maps
 to provide detailed information on different engineering geological
aspect
• grade of weathering, joint patterns, mass permeability,
foundation conditions
 Engineering purposes information as well as various other aspects
of engineering geology are covered on the multipurpose maps
 To produce detailed and reliable engineering geological map
 different aspects should be detailed:
• expansive soils, measured joints, faults, residual soils, transported
soils, geology of the location, rock slopes, outcrops, underlying
bedrock, foundations, excavations, geologic structure, lithology
and composition, mineralogy, texture, color, degree of weathering,
alteration, etc.

358

359

360

361

362
Multi-Purpose Engineering Geological Map

363

364

365

366

367

CHAPTER 10
River Engineering and Hydraulic
Structures

Head-works
• Any hydraulic structure which supplies water to the off-taking
canal is called a headwork.
• Headwork may be
1. Storage headwork
2. Diversion headwork
• A Storage headwork comprises the construction of a dam onthe
river.
• It stores water during the period of excess supplies and releases
it when demand overtakes available supplies.
• A diversion headwork serves to divert the required supplyto

Diversion Head-works
A diversion head works is a structure constructed across a
river for the purpose of raising water level in the river so that
it can be diverted into the offtaking canals.
Diversion headworks are generally constructed on the
perennial rivers which have adequate flow throughout the
year
A diversion head works differs from a storage work or a dam.
A dam is constructed on the river for the purpose of creating
a large storage reservoir.
The storage works are required for the storage of water on a
non-perennial river or on a river with inadequate flow
throughout the year.
On the other hand, in a diversion head works, there is very
little storage, if any.

Diversion… cont’d
Functions of Diversion Headworks:
It raises the water level on its upstreamside.
It regulates the supply of water intocanals.
It controls the entry of silt intocanals
It creates a small pond (not reservoir) on its upstream and provides some
pondage.
It helps in controlling the vagaries of theriver.

Hydraulic Structures… cont’d
Weir or Barrage
A weir is a raised concrete crest wall constructed across
the river.
It may be provided with small shutters (gates) on its top.
In the case of weir, most of the raising of water level or
ponding is done by the solid weir wall and little with by
the shutters.
A barrage has a low crest wall with high gates.
As the height of the crest above the river bed is low most
of the ponding is done by gates.
During the floods the gates are opened so afflux is very
small

Diversion… cont’d
A weir maintains a constant pond level on its upstream side so that the
water can flow into the canals with the full supply level.
If the difference between the pond level and the crest level is less than
1.5 m or so, a weir is usually constructed.
On the other hand, if this difference is greater than 1.50 m, a gate-
controlled barrage is generally more suitable than a weir.
In the case of a weir, the crest shutters are dropped during floods so
that the water can pass over the crest.
During the dry period, these shutters are raised to store water up to the
pond level.
Generally, the shutters are operated manually, and there is no
mechanical arrangement for raising or dropping the shutters.
On the other hand, in the case of a barrage, the control of pondage
and flood discharge is achieved with the help of gates which are

Types of Weirs
Vertical drop weirs
Rock Fill weirs
Concrete glacis or sloping weirs.
• Wall type structure on a horizontal concrete floor.
•Shutters are provided at the crest, which are dropped during
floods so as to reduce afflux.
•Water is ponded upto the top of the shutters during the rest of the period.
1.Vertical Drop Weirs

Cont’
d
•In a rock fill type weir, there are a number of core
walls.
•The space between the core walls is filled with the
fragments of rock.
•A rock fill weir requires a lot of rock fragments
and is economical only when a huge quantity of
rock fill is easily available near the weir site.
•It is suitable for fine sand foundation.
2. Rockfill Weirs

•The crest has glacis (sloping floors) on u/s as well as d/s.
There are sheet piles driven upto the maximum scour depth at
the u/s and d/s ends of the concrete floor.
•Sometimes an intermediate pile is also driven at the
beginning of the u/s glacis or at the end of d/s glacis.
•The main advantage of a sloping weir over the vertical drop
weir is that a hydraulic jump is formed on the d/s glacis for
the dissipation of energy.
3. Sloping/Glacis Weirs Cont’d

Site Selection of diversion headworks
The river section at the site should be narrow and well-defined.
The river should have high, well-defined, inerodible and non-
submersible banks so that the cost of river works is minimum.
The canals taking off from the diversion headworks should be quite
economical and should have a large commanded area.
There should be suitable arrangement for the diversion of
river during construction.
The site should be such that the weir (or barrage) can be aligned at right
angles to the direction of flow in the river. uniform flow and length of
the weir - minimum.

Cont’d
• Good foundation should be available at the site.
The required materials of construction should be available near the
site.
The site should be easily accessible by road or rail.
The overall cost of the project should be a minimum.

Irrigation/hydraulic structures for the diversion and distribution works
such as weirs, barrages, head regulators, distributary head regulators,
cross regulators, cross drainage works, etc. These structures are
generally founded on alluvial soils which are highly pervious.
These soils are easily scoured when the high velocity water passes
over the structures.
The failures of weirs constructed on the permeable foundation may
occur due to various causes:
Failure due to subsurface flow
Failure due to surface flow
Modes of failure

Cont’d
1. Failure due to Subsurface Flow
The failure due to subsurface flow may occur by
1. Piping due to Exit Gradient
2. Rupture of floor due to uplift
Failure by rupture of floor
The water percolating through the foundation exerts an upward
pressure on the impervious floor, called the uplift pressure.
If the weight of the floor is not adequate to counterbalance the
uplift pressure, it may fail by rupture.

Cont’d
Piping failure
Piping occurs below the weir if the water percolating through the
foundation has a large seepage force when it emerges at the d/s end of
the impervious floor.
When the seepage force exceeds a certain value, the soil particles
are lifted up at the exit point of the seepage.
With the removal of the surface soil particles, there is further
concentration of flow in the remaining portion and more soil
particles are removed.
This process of backward erosion progressively extends towards the
upstream side, and a pipe-like hollow formation occurs beneath the
floor.
The floor ultimately subsides in the hollows so formed and fails.
This type of failure is known as piping failure.

Cont’d
2. Failure due to Surface Flow
The failure due to surface flow may occur by suction pressure due to
hydraulic jump or by scouring of the bed.
(a) Failure by suction pressure
In the glacis type of weirs, hydraulic jump is formed on the d/s glacis.
In this case, the water surface profile in the hydraulic jump channel is
much lower than the subsoil.
Therefore uplift pressure occurs on the glacis.
This uplift pressure is known as the suction pressure.
If the thickness of floor is not adequate, the rupture of floor may occur.
(b) Failure by scour
During floods, scouring occurs in the river bed.
The bed of the river may be scoured to a considerable depth.
If no suitable measures are adopted, the scour may cause damage to

Flow Control Structures
groynes
bendway weir
engineered log jam

Types of flow control structures
 Guide banks
 Dykes
 Jetties
 Vanes
 Bendway Weirs
 Drop Structures
 Fences
 Engineered Log Jams
This presentation focuses on vanes, drop structures,
engineered log jams, bendway weirs, and guidebanks.

Vanes
Vanes act to guide the flow away from bank, to reduce
bank erosion, promote local sedimentation and
encourage vegetation growth. Vanes include;
1. deflectors
2. vane dykes
deflectors

Vanes: deflectors and dykes
deflectors:
divert flow from bank
creates deeper channel
typically rock construction
Vane dykes:
point downstream
counteracts secondary flow
currents
promotes bank erosion when
overtopped
high torque can lead tofailure
constructed of rock, gabions and
other resistant material
deflectors

Grade Control & Drop Structures
Gabion drop structure, in process of failing…

Engineered Log Jams
•36-48” dia logs with and
without root wads
•installed into the banks to
act like spurs or hard
points.
•can also be installed in the
channel to divert flow
• permeable to flow
• Logjams form where large quantities of wood
accumulate, usually at flow obstructions such as snags
or bridge piers, although logjams can also form along
meander banks or in channel avulsions.

Bendway Weirs
•Bendway Weir serious of
upstream angled low elevation
stone sills.
•Improve lateral stream stability
and flow alignment
•Improve inadequate navigation
channel width at bends
• Reduce outer bank velocity
•Produces a better alignment of
flow through the bend and
downstream crossing

THANK YOU & WISH
YOU ALL THE BEST!!!
391
30

WU_Engineering geology_lecture note_Elias.pdf

More Related Content

What's hot (20)

Similar to WU_Engineering geology_lecture note_Elias.pdf (20)

More from ELIASASSEFA3 (15)

Recently uploaded (20)

WU_Engineering geology_lecture note_Elias.pdf