Geotechnical Engineering
For
Civil Engineering
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Syllabus Geotechnical Engineering
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Syllabus for Geotechnical Engineering
Origin of soils, soil classification, Three-phase system, fundamental definitions, Relationship and interrelationships, permeability & seepage, Effective stress principle, consolidation, compaction, shear strength. Sub-surface investigations- scope, drilling bore holes, sampling, penetration tests, plate load test. Earth pressure theories, effect of water table, layered soils. Stability of slopes-infinite slopes, finite slopes. Foundation types-foundation design requirements. Shallow foundations-bearing capacity, effect of shape, water table and other factors, stress distribution, settlement analysis in sands & clays. Deep foundations - pile types, dynamic & static formulae, load capacity of piles in sands & clays, negative skin friction.
Analysis of GATE Papers
(Geotechnical Engineering)
Year Percentage of marks Overall Percentage
2013 15.00
15.75%
2012 14.00
2011 18.82
2010 20.00
2009 16.00
2008 16.66
2007 15.33
2006 14.00
2005 16.00
2004 17.33
2003 18.67
2002 13.33
2001 13.33
2000 12.00
Contents Geotechnical Engineering
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C O N T E N T S
Chapter Page No.
#1. Three Phase System Fundamental Definitions & Relationship 1 – 12
Origin of Soil 1
Introduction 1
Water Content Density and Unit Weight 1 – 4
Pyrometer Method 4 – 5
Solved Examples 6 – 8
Assignment 9 – 10
Answer Keys 11
Explanations 11 – 12 #2. Index Properties and Soil Classification 13 – 24
Properties of Soil Classification 11 - 14
Particle Size Distribution Curve 15 – 17
Classsification of Soil 17 – 18
Solved Examples 19 – 20
Assignment 21 - 22
Answer Keys 23
Explanations 23 – 24
#3. Permeability and Seepage 25 – 40
Permeability 25
Discharge Velocity and Seepage Velocity 25 - 26
Determination of Coefficient of Permability 26 - 27
Capallarity Permeability Test 27 – 28
Permeability of Stratified Soil Deposits 29 – 30
Deflection of Flow Line at Interface of Dissimilar Soil 31 – 32
Solved Examples 33 – 35
Assignment 36 - 38
Answer Keys 39
Explanations 39 – 40
#4. Consolidation 41 – 55
Introduction 41
Consolidation of Laterally Confined Soil 41 - 42
Consolidation Settlement 42 – 44
Determination of Co-efficient of consolidation 44 – 46
Solved Examples 47 – 51
Assignment 52 - 53
Answer Keys 54
Explanations 54 – 55
Contents Geotechnical Engineering
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#5. Compaction 56 – 65 Introduction 56
Optimum Water Content 56 - 57
Zero Air Voids Line 57
Comparsion of Standard and Modifical Proctor Test 57 – 59
Factor Effective Compaction 59 – 61
Solved Exampes Assignnment Answer Keys Explanations
62 – 63 64 65 65
#6. Stress Analysis 66 – 74
Introduction 66
Concentrated Force 66 – 68
Vertical Pressure Under a Uniformaly Loaded Circular Area 68 - 69
Contact Pressure 69
Solved Examples 70 – 71
Assignment 72 – 73
Answer Keys 74
Explanations 74
#7. Shear Strength 75 – 93 Introduction 75
Mohr’s Stress Circle & Coulumb Failure Theory 75 – 76
Effective stress principal 77 - 78
Stress condition in Soil during Triaxial Testing 78 – 79
Unconfined Compression Test 79 – 81
Skempton’s Pore Pressure Parameters 81 – 82
Shear Strength of Cohensive Soils 82 - 83
Solved Examples 84 – 88
Assignment 89 – 91
Answer Keys 92
Explanations 92 - 93 #8. Surface Investigations 94 – 105
Introduction 94
Method of Site Investigation 94 - 95
Type of Site Exploration 95 – 96
Methods of Site Exploration 96
Boring Methods 96 – 98
Soil samples 98 – 102
Assignment 103 - 104
Answer Keys 105
Explanations 105
#9. Earth Pressure 106 – 126
Introduction 106
Types of Earth Pressure 106 – 107
Contents Geotechnical Engineering
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Rankine’s Theory 107 – 112
Coulumb’s Wedge Theory 112 – 114
Solved Examples 115 – 121
Assignment 122 - 123
Answer Keys 124
Explanations 124 – 126
#10. Stability of Slopes 127 – 138 Introduction 127
Stability Analysis 127 – 131
Friction Circle Method 131 – 133
Stability of Slopes of Earth Dam 133
Solved Examples 134 – 135
Assignment 136
Answer Keys 137
Explanations 137 – 138
#11. Bearing Capacity 139 – 158
Types of Foundation Definitions
139 – 140 140 - 141
Types of Bearing Capacity Failures 141 – 142
Terzagj’s Analysis 142 – 144
Skempton’s Bearing Capacity Theory 144 – 145
Settlement Criteria of Footings 145 – 146
Solved Examples 147 – 153
Assignment 154 – 156
Answer Keys 157
Explanations 157 – 158
#12. Pile Foundation 159 -172
Classification of Piles 159
Pile Capacity 159 – 162
Feld’s Rule 162 – 164
Solved Examples 165 – 168
Assignment 169 - 170
Answer Keys 171
Explanations 171 – 172
Module Test 173 – 185 Test Questions 173 – 178
Answer Keys 179
Explanations 179 - 185 Reference Books 186
Chapter 1 Geotechnical Engineering
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Chapter 1
Three Phase System, Fundamental Definitions and Relationship
Origin of Soil
Soil is complex material produced by weathering of solid rock weathering is caused by physical agencies and geological cycle followed is weathering transportation, denudation and upheaval.
Residual Soil: Soil which remain in place directly over parent rock. Transported Soil: are transported by physical agencies like wind, water, etc… Water Transported Soil: are called alluvial, marine or lacustrine. Lacustrine soil find their origin in lakes Alluvial soil in flowing water and marine soil in seas Air blown soil are called aoline Loess is windblown silt or salty clay. Accumulation of decaying and chemically deposited vegetable matter under excessive
moisture results in formation of cumulous soil (peat and muck).
Introduction Soil mass is 3 phase system consisting of solid particles, water and air. In dry soil, only soil particles and air voids are present. As shown in figure. Figure 1 (a)
shows the element of natural soil and figure 1(b) shows elements separated into 3 phases.
Water Content, Density and Unit Weights a. Water Content: Ratio of weight of water to weight of solids, Ws
b. Density of Soil: Mass of soil per unit volume is called density of soil i. Bulk density: Also known as moist density is total mass M of soil per unit of its total
volume.
V
Water Solids
Wa=0
Ww
Ws
Or
wd
Va
Vw
VS
Figure 1 (a)
Element of Soil Figure 1 (b)
Three phase system
Chapter 1 Geotechnical Engineering
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ii. Dry density (δd): Mass of solids per unit of total volume (prior to drying)
iii. Density of Solid (δs): Mass of soil solids (Md) per unit volume of solids
iv. Saturated density: When soil mass is saturated its bulk density is called saturated density (δ sat)
v. Submerged density: Submerged massof solids (Md) sub per unit of total volume.
( )
Unit Weight of Soil Mass
i. Bulk unit weight ( )= Total weight W of a soil mass per unit of its volume V
ii. Dry unit weight: weight of solids per unity of its total volume of soil mass
iii. Unit weight of solids: weight of soil solids is weight of soil solids Wd per unit volume of solids (Vs)
iv. Saturated unit weight (r sat): When soil mass is saturated its bulk umit weight is called saturated unit weight.
v. Submerged unit weight: (r1)→ Submerged weight of soil solids (Wd) sub per unit of total volume (V) of soil mass.
( )
Specific Gravity Specific gravity G is defined as ratio of weight of given volume of soil solids at given Temperature to weight of equal volume of distilled water at same temperature.
The apparent specific gravity denotes mass of soil to equal mass of water
Void Ratio, Porosity and Degree of Saturation Void Ratio:(
) or void ratio is ratio of volume
of voids to volume of soil solids in given soil mass
Porosity: The porosity n of given soil sample is ratio of volume of voids to total volume of given soil mass.
Relation between l and n
( )⁄
Chapter 1 Geotechnical Engineering
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Degree of Saturation: Volume of water to volume of voids is called degree of saturation
→ for perfectly dry sample, S=0 and for perfectly saturated sample, S=1. Percentage of air Voids: Ratio of volume of air voids to total volume of soil mass and is expressed as
Air content: Air content ac is defined as ratio of volume of air voids to the volume of void
Density Index and Relative Comp Active
D.I =
The term density Index is applicable only for cohesion less soil. Relative compaction: Relative compaction is defined as
,
Where rd, max is obtained from compaction test.
Functional Relationships i. Relation between l,G and s
The term lw is water void ratio and other symbols have their usual meaning.
ii. Relation between ,
,
( )( )
iii. Relation between na,n and ac
iv. Relation between , ( )
Also ( ) v. Relation between ,
( )
vi. Relation between , , ,
Chapter 1 Geotechnical Engineering
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( )
,
( )
( )
vii. Relation between ,
( ) viii. Relation between , ,
( )
Pyrometer Method
This is also a quick method of determining the water content of those soils whose specific
gravity G is accurately known. Pycnometer is large size density bottle of about 900 ml capacity.
Test Procedure
1. Take a clean, dry Pycnometer, and find its mass with its cap and washer (M1)
2. Put about 200g 400g of wet soil sample in the Pycnometer and find its mass with its cap
and washer (M2)
3. Full the Pycnometer to half its height and mix it thoroughly with the glass rod. Add more
water, and stir it. Replace the screw top and fill the Pycnometer flush with the hole in the
conical cap. Dry the Pycnometer from outside, and its mass (M3).
4. Empty the Pycnometer, clean it thoroughly, and fill it with clean water to the hole of the
conical cap, and find its mass (M4)
The water content is then calculated from the following expression:
[*
+ *
+ ]
The above expression can be derived with reference to if Md is the mass of soil particles;
the volume of solid particles will be equal to Md/G. Thus, if the solids from (iii) are
replaced with water of mass , we get the mass M4 indicated in (iv). Thus,
*
+
, ( )
Now mass of water Mw in the wet soil sample = (M2-M1)-Md
Chapter 1 Geotechnical Engineering
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*
+ [*
+ *
+ ]