Civil Engineering : Geotechnical engineering, THE GATE ACADEMY

Geotechnical 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


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


Assignment 36 - 38

Answer Keys 39


#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


Assignment 52 - 53

Answer Keys 54



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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


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



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


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Rankine’s Theory 107 – 112

Coulumb’s Wedge Theory 112 – 114



Answer Keys 124


#10. Stability of Slopes 127 – 138 Introduction 127

Stability Analysis 127 – 131

Friction Circle Method 131 – 133

Stability of Slopes of Earth Dam 133


Assignment 136

Answer Keys 137


#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



Answer Keys 157


#12. Pile Foundation 159 -172

Classification of Piles 159

Pile Capacity 159 – 162

Feld’s Rule 162 – 164



Answer Keys 171


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



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

( )⁄



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 , , ,



( )

,

( )

( )

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



*

+ [*

+ *

+ ]

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Civil Engineering : Geotechnical engineering, THE GATE ACADEMY