GATE Geotechnical Engineering Engineering

Geotechnical Engineering For Civil Engineering

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Syllabus

Geotechnical Engineering

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

2013

15.00

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

Overall Percentage

15.75%

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Contents

Geotechnical Engineering

CONTENTS

#1.

Chapter

Page No.

Three Phase System Fundamental Definitions & Relationship

1 – 12

       

#2.

Origin of Soil Introduction Water Content Density and Unit Weight Pyrometer Method Solved Examples Assignment Answer Keys Explanations

1 1 1–4 4–5 6–8 9 – 10 11 11 – 12

Index Properties and Soil Classification

13 – 24

      

#3.

#4.

Properties of Soil Classification Particle Size Distribution Curve Classsification of Soil Solved Examples Assignment Answer Keys Explanations

Permeability and Seepage

         

Permeability Discharge Velocity and Seepage Velocity Determination of Coefficient of Permability Capallarity Permeability Test Permeability of Stratified Soil Deposits Deflection of Flow Line at Interface of Dissimilar Soil Solved Examples Assignment Answer Keys Explanations

Consolidation

       

Introduction Consolidation of Laterally Confined Soil Consolidation Settlement Determination of Co-efficient of consolidation Solved Examples Assignment Answer Keys Explanations

11 - 14 15 – 17 17 – 18 19 – 20 21 - 22 23 23 – 24

25 – 40 25 25 - 26 26 - 27 27 – 28 29 – 30 31 – 32 33 – 35 36 - 38 39 39 – 40

41 – 55 41 41 - 42 42 – 44 44 – 46 47 – 51 52 - 53 54 54 – 55

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Contents

#5.

Geotechnical Engineering

Compaction

        

Introduction Optimum Water Content Zero Air Voids Line Comparsion of Standard and Modifical Proctor Test Factor Effective Compaction Solved Exampes Assignnment Answer Keys Explanations

56 – 65 56 56 - 57 57 57 – 59 59 – 61 62 – 63 64 65 65

#6.

Stress Analysis  Introduction  Concentrated Force  Vertical Pressure Under a Uniformaly Loaded Circular Area  Contact Pressure  Solved Examples  Assignment  Answer Keys  Explanations

66 – 74 66 66 – 68 68 - 69 69 70 – 71 72 – 73 74 74

#7.

Shear Strength  Introduction  Mohr’s Stress Circle & Coulumb Failure Theory  Effective stress principal  Stress condition in Soil during Triaxial Testing  Unconfined Compression Test  Skempton’s Pore Pressure Parameters  Shear Strength of Cohensive Soils  Solved Examples  Assignment  Answer Keys  Explanations

75 – 93 75 75 – 76 77 - 78 78 – 79 79 – 81 81 – 82 82 - 83 84 – 88 89 – 91 92 92 - 93

#8.

Surface Investigations  Introduction  Method of Site Investigation  Type of Site Exploration  Methods of Site Exploration  Boring Methods  Soil samples  Assignment  Answer Keys  Explanations

94 – 105 94 94 - 95 95 – 96 96 96 – 98 98 – 102 103 - 104 105 105

#9.

Earth Pressure  Introduction  Types of Earth Pressure

106 – 126 106 106 – 107

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Contents

     

Rankine’s Theory Coulumb’s Wedge Theory Solved Examples Assignment Answer Keys Explanations

Geotechnical Engineering

107 – 112 112 – 114 115 – 121 122 - 123 124 124 – 126

#10.

Stability of Slopes  Introduction  Stability Analysis  Friction Circle Method  Stability of Slopes of Earth Dam  Solved Examples  Assignment  Answer Keys  Explanations

127 – 138 127 127 – 131 131 – 133 133 134 – 135 136 137 137 – 138

#11.

Bearing Capacity  Types of Foundation  Definitions  Types of Bearing Capacity Failures  Terzagj’s Analysis  Skempton’s Bearing Capacity Theory  Settlement Criteria of Footings  Solved Examples  Assignment  Answer Keys  Explanations

139 – 158 139 – 140 140 - 141 141 – 142 142 – 144 144 – 145 145 – 146 147 – 153 154 – 156 157 157 – 158

#12.

Pile Foundation  Classification of Piles  Pile Capacity  Feld’s Rule  Solved Examples  Assignment  Answer Keys  Explanations

159 -172 159 159 – 162 162 – 164 165 – 168 169 - 170 171 171 – 172

Module Test

  

Test Questions Answer Keys Explanations

Reference Books

173 – 185 173 – 178 179 179 - 185

186

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Chapter 1

Geotechnical Engineering

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.

V

Water

Va

Wa=0

Vw

Ww

VS

Ws Or wd

Solids Figure 1 (a) Element of Soil

Figure 1 (b) Three phase system

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. 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

Geotechnical Engineering

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) Submerged density: Submerged massof solids (Md) sub per unit of total volume. ( )

v.

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 ⁄( ) 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 2

Chapter 1

Geotechnical Engineering

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

v.

( ) Also Relation between

(

vi.

,

(

)

,

)

Relation between , , , 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 3

Chapter 1 (

)

(

(

vii. viii.

Geotechnical Engineering

,

)

)

Relation between , ( ) 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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Chapter 1

*

+

[*

+*

+

Geotechnical Engineering

]

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