GATE Geotechnical Engineering Engineering

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Geotechnical Engineering

For

Civil Engineering

By

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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

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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

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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

 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

 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  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

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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

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Chapter 1 Geotechnical Engineering

THE GATE ACADEMY PVT.LTD. H.O.: #74, KeshavaKrupa (third Floor), 30th Cross, 10th Main, Jayanagar 4th Block, Bangalore-11 : 080-65700750,  [email protected] © Copyright reserved. Web: www.thegateacademy.com Page 1

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

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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 ( )⁄

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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 , ( )

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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,

* + , ( )

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