Basic and Applied Soil Mechanics

158 Pages·2007·13.09 MB·English

by  Gopal Ranjan and A.S.R. Rao

Gopal
A.S.R. Rao

A NEW AGE INTERNATIONAL PUBLISHERS |
Copyright © 1991, 2000 New Age International (P) Ltd., Publishers
First Edition : 1991
Second Edition : 2000
Reprint : 2005

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ISBN : 81-224-1223-8
789 1011 12 13 14 15

Published by New Age International (P) Ltd.,
4835/24, Ansari Road, Daryaganj, New Delhi-110 002 ana
printed in India at Print Perfect, New Delhi-110 064.
Contents

Preface to the Second Edition y
Preface to the First Edition vi
L_INTRODUCTION 1

1.1 _ Soil, Soil Mechanics and Soil Engineering 1
1.2_ Civil Engineering Problems Related to Soils _1
1.3 Complexity of Soil Nature__2
14 _ Historical Development_ 3
15_Soil Formation and Soll Types_4
1.6 __Regional Soil Deposits of India_6
IS - WATER - AIR RELATI
2.1 Phase Diagram 10
2.2__ Simple Definitions 11
2.3 _ Some Important Relationships 14
2.4___Water Content Determination 20
25 _ Specific Gravity of Solids Determination 22
2.6 In Situ Unit Weight Determination 23
2.7 __Index Properties of Soils _25
2.8 Grain shape 25
2.10 Consistency of Clays : Atterberg Limits 34
2.11 Significance of other Soil Aggregate Properties 43
‘4._CLASSIFICATION OF SOILS 1
‘2.1__Introduction _77
3.2__The Unified Soil Classification System _77
3.3__ AASHTO Soil Classification System _78
3.4__ Indian Standard Soil Classification System _79
3.5___ Applications of Soil Classification 85
4._SOUL STRUCTURE AND CLAY MINERALS
4.1 Introduction 91
42 Clay Minerals _92
43 Clay Water Relations 98
44 Clay Particle Interaction 101,
Vim Contents
S Sails Fatnio 102

4.6 Granular Soil Fabrics 103

5._SOIL COMPACTION

106

‘S.1__Introduction 106

52 Tests_107

5.3 Factors Affecting Compaction 109

5.4 _ Structure and Engineering behaviour of Compacted Conesive Soil_113
5.5 Compaction in the Field 117

5.6 Compaction Specifications and Field Control_119

6 PRINCIPLE OF EFFECTIVE STRESS, CAPILLARITY AND PERMEABILITY
6.1 Introduction 128
62 _ Principle of Effective Stress 128
6.3 Physical Meaning of Effective Stress 130
6.4 Capillarity in Soils _132
6.5 Permeability of Soils 137
6.6 Types of Head, Seepage Forces and Quicksand Condition 148
‘7._SEEPAGE THROUGH SOILS

‘L.1__Introduction 173
7.2__‘Two- Dimensional Flow — Laplace's Equation _173
73° FlowNets 175
14__Unconfined Flow 183
7.5 _ Seepage in Anisotropic Soil Conditions 186
7.6 _ Flow through Nonhomogeneous Sections 188
‘L.1__Prevention of Erosion — Protective Filters 189
8, VERTICAL STRESSES BELOW APPLIED LOADS
8.1 Introduction 200
8.2 Boussinesq Equations 200
83 Vertical Stress Distribution Diagrams 202
84 Vertical Stress Beneath Loaded Areas 203
‘5 New Mark's Influence Chart 208
8.6 __ Approximate Stress Distribution Methods for Loaded Areas_210
8.7. Westergaard’s Equation 212
9. COMPRESSIBILITY OF SOIL AND CONSOLIDATION
9.1 Introduction 221
9.2 Components of Total Settlement 221
93 Compressibility 222
9.4, Time-Rate of Consolidation 227
9.5 Consolidation Test 237
9.6 Computation of Settlement 243

221
Contents 1X

9.7 _ Extrapolation of Field Consolidation Curve _246
9.8 Compression Index — Some Empirical Correlations 247
9.9 Secondary Consolidation Settlement 248
9.10 Settlement Analysis 249
9.11 Vertical sand Drains 253
10, SHEAR STRENGTH OF SOILS 287
10.1 Introduction 287
10.2 Stress at a Point—Mohr Circle of Sess 287
10._Mechanism of Shear Resistance 289
10.5 Measurement of Shear Strength 296
10.6 _ Shear Strength of Clay Soils _303
10:7 Shear Strength of Sands 311
10.8 Drainage Conditions and Strength Parameters 316
10.9 Stress Paths 317
10.10 Pore Pressure Parameters 324
10.11 Elastic Properties of Soil 328
11. STABILITY OF SLOPES 353
ULL Introduction 353
11.2. Infinite Slopes and Translational Slides 354
11.3. Definitions of Factor of Safety 358
11.4. Finite Slopes — Forms of Slip Surface 358
11.5. Limiting Equilibrium Method and Critical Stages in Stability 359
11.6 Total Stress and Effective Stress Methods of Analysis 359
11.7 4=0 Analysis (Total Stress Analysis) 360
11.8 _c—6 Analysis — Method of Slices _362
1.9 Location of the Mast Critical Circle 363
11.10 Stability of Earth Dam Slopes 364
11.11 Friction Circle Method 367
11.12 Taylor's Stability Number_368
rm 3's Method of Stabili
11.14 Use of Stability Coefficients _374
11.15 Effect of Earthquake Force—Pseudo-static Analysis 376

123_Farth Pressure at Rest 392
12.4 Rankines Theory of Earth Pressure 394
12.5 Coulomb's Theory of Earth Pressure 403
X Contents

12.6 Coulomb Equations for c= 0 Backfills _406
12.7 Culmann’s Graphical Method 407
Passive Barth Preanre ~ Friction Ch
129 Design Considerations for Retaining Walls 413
13. ARCHING IN SOILS AND BRACED curs as
13.1__Arching in Soils 435,
13.2 Theories of Arching 435
13.3 Cain's Theory 437
13.4 Tunnels Through Sand _439
13.5_Braced Excavations 440
13.6 Earth Pressure against Bracings in Cuts 442
13.7_Heave of The Bottom of Cut in Soft Clays 444
138 SimtLoads 444
13.9 Deep Cuts in Sand _ 446
13.10 Deep Cuts in Saturated, Soft to Medium Clays 447
14, FLEXIBLE RETAINING STRUCTURES AND COFFER DAMS 452,
14.1 Introduction 452
142 Cantilever Sheet Pile Wall 453
143° Anchored Bulkhead 457
144 Coffer Dams 463
18. SHALLOW FOUNDATION! amg
15.L_Introduction 474
15.2_ General Requirements of Foundations _476
15.3 Location and Depth of Foundation _ 476
15.4 Terminology 478
15.5. Choice of Net Allowable Bearing Pressure 479
15.6 Bearing Capacity of Shallow Foundations 482
15.7 Settlement of Shallow Foundations 500
15.8 Allowable Bearing Pressure 517
15.9 Steps Involved in the Proportioning of Footings 521
16. PILE FOUNDATIONS 546
16.1_Introduction 546
16.2 Uses of Piles 546
16.3 Types of Piles _547
16.4 Cast In Situ Pile Construction 549
16.5 Selection of Pile Type 552
16.6 Types of Foundations to Suit Subsoil Conditions _553
16.7_Pile Driving 556
16.8 Pile Load Capacity in Compression _556
Goments Xt

169 Static Pile Load Formulae 556
16.10 Load Test on Piles 565

16.11 Dynamic Pile Formulae 569
16.12 Correlations with Penetration Test Data 572

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16.13 Group Action of Pies 574 66d acsT qoncwede Linnie aneaT bie 22F
16.14 Negative Skin Friction 580 Ok) esTroromoniems O81
16.15 Laterally Loaded Piles 582 ok) (TMA) ws ratoemouresn 111
16.16 Piles Subjected to Uplift Loads 586 £0) abndiaM levizedqooi £1.01
17, WELL FOUNDATIONS 2ea 740.1 slewla 1 D4
17.1 Introduction 604 $e) noqasl noiteyitesenl ane BLT
47.2 “Types of Wells or Caissons_604 2102 AVIZHAIXA YO 2AOLTAGHUOT OS
17.3 Components of a Well Foundation 605 COT anizaubownt 10S
17.4 Shapes of Wells 607 SOY alin? svionegx’t Ww woinatiasbl 6.06
Sept of Well Foundloa 08 En w2-wwires sait enninibaod blart EOE
17.6 Forces Acting on Well Foundation 610 TOF gnillaw2 To roonaupsens) FOE
17.7 Lateral Stability of Well Foundation 611 j5- jig svisneqe awort to ngiead 2 OE
17.8 Construction and Sinking of a Well_627 Zit _altyM omo® 2ionkt omoz 0.
18_ MACHINE FOUNDATIONS

ol81 Introduction 639 gnirgonign’d aoitsbaue'l bue zaimedt29M lioe no 2abo <4

1482. Terminology 639 gairoonigndl io? mi atinls 12 Yo 920) aT

483 Design Criteria for Satisfactory Action of a Machine Foundation 641 Anutl noiteauQ)

{184 Theory of Linear Welghtless Spring 641 vobal

18.5 Methods of Analysis of a Block Foundation 645
18.6 Soil Spring Constants 646
18.7 Determination of Soil—Spring Constants 646
188 Damping 651
18.9 Degrees of a Freedom of Block Foundation 652
18.10 Vertical Vibrations of a Block Foundation 653
18.11 Rocking Vibrations of a Block Foundation 654
18.12 Pure Sliding of a Block Foundation 657
18.13 Yawing of a Block Foundation 657
18.14 Simultaneous Rocking, Sliding and Vertical Vibrations of a Block Foundation 658
18.15 Indian Standard on Design and Construction of Foundations for Reciprocating
Machines 660
19, SOIL EXPLORATION 69
19.1 Introduction 669
19.2. Methods of Exploration 669
19.3, Methods of Boring 669

194 Soil Samples _672
XI Contents

19.5 Soil Samplers and Sampling 674
19.6 Number and Disposition of Trial Pits and Borings 677
19.7 Depth of Exploration 677
19.8 Ground Water Observations 678
19.9 Field Tests vis-a-vis Laboratory Tests 679
19.9 Penetrometer Tests 680
19.11 Pressuremeter Test (PMT) 686
19.12 Geophysical Methods 692
19.13 Borehole Logs 695,
19.14 Site Investigation Report _ 697
20, FOUNDATIONS ON EXPANSIVE SOILS

702

20.1_Introduction 702
20.2 Identification of Expansive Soils 702

20.3 Field Conditions that Favour Swelling 706
20.4 Consequences of Swelling 707

20.5 Design of Foundations on Expansive Soils 708
20.6 Some Facts, Some Myths 715

IS: Codes on Soil Mechanics and Foundation Engineering

‘The Use of SI Units in Soil Engineering

74

Question Bank :

Index

753
1

Introduction

1.1 SOIL, SOIL MECHANICS AND SOIL ENGINEERING

‘The term ‘soil’ has different connotations for scientists belonging to different disciplines. The definition given
toasoil by an agriculturist ora geologist is different from the one used by a civil engineer. To an agriculturist,

il merely means the top layer of the earth which is responsible for supporting plant life. Even to a geologist,
soil is the thin outer layer of loose sediments within which plant roots are present. A geologist refers to the rest
Of the earth's crust as rock, irrespective of how strong or weak the bonding forces of the sediments are. For a
civil engineer, soils mean all naturally occurring, relatively unconsolidated earth material—organic or
inorganic in character—that lies above the bedrock. According to Terzaghi, soils can be broken down into
their constituent particles relatively easily, such as by agitation in water. On the other hand, rocks are an
agglomeration of mineral particles which are bonded together by strong molecular forces. Often, this distinction
between soils and rocks is not clear-cut. Many a hard soil can also be termed as soft rock or vice versa. Rocks
can be the massive bedrock or large fragments of gravel, pebbles, etc.. within a soil.

Soil Mechanics is the branch of civil engineering that concerns the application of the principles of
mechanics, hydraulics and to a smaller extent, chemistry, to engineering problems related to soils. The study
Of the science of soil mechanics equips a civil engineer with the basis scientific tools needed to understand soil
behaviour. This is by no means sufficient to provide satisfactory solutions to soil problems. The reasons for
this will be clear later.

Rock Mechanics is defined as the science dealing with the application of the principles of mechanics to
the understanding of the behaviour of rock masses.

Soil Engineering isa broader term which eniompasses notonly soil mechanics but also geology, structural
engineering, soil dynamics and many other disciplines which are often essential to obtain practical solutions
to problems of soil. Geotechnical Engineering is relatively a new term and includes soil mechanics, rock
mechanics, soil engineering and rock engineering. Geotechnical engineers need to have a proper understanding,
of engineering geology, since there isa significant overlap between the two disciplines.

‘The present volume is strictly restricted to the study of the engincering behaviour of the soil mass.

1.2. CIVIL ENGINEERING PROBLEMS RELATED TO SOILS

A civil engineer has to deal with soils in their diverse roles. Every civil engineering structure, whether it be a
ing, a bridge, a tower, an embankment, a road pavement, a railway line, a tunnel or a dam, has to be
2 Basic and Applied Soil Mechanics

founded on the soil (assuming that a rock stratum is not available) and thus shall transmit the dead and live
loads to the soil stratum. Soil is, therefore, the ultimate foundation material which supports the structure. The
proper functioning of the structure will, therefore, depend critically on the success of the foundation element
resting on the subsoil, Here the term foundation is used in the conventional sense, namely, a substructure that
distributes the load to the ultimate foundation, namely, the soi.

Soil is also the most abundantly available construction material. From ancient times, man has used soil
for the construction bf tombs, monuments, dwellings, and barrages for storing water. In modern times, the use
of earth for building dams and for constructing pavements for highway’ and airfields is an important aspect of
civil engineering. Many questions concerning the design and construction of these structures need to be
answered before satisfactory solutions are obtained.

Inthe design and construction of underground structures such as tunnels, conduits, power houses, bracings
for excavations and earth retaining structures, the role of soi is again very crucial. Since the soil isin direct
contact with the structure, it acts as a medium of load transfer and hence for any analysis of forces acting on
such structures, one has to consider the aspect of stress distribution through the soil. This, however, cannot be
done by considering the behaviour of the structure in isolation of the soil or by treating the soil independently
Of the structure, The structure, too, causes stresses and strains in the soil, while the stability of the structure
itself is affected by soil behaviour. The class of problems where the structure and soil mutually interact, are
known as soi-structure interaction problems.

‘There are a host of other civil engineering problems related to soils. For designing foundations for
machines such as turbines, compressors, forges etc.. which transmit vibrations to the foundation soil, one
has to understand the behaviour of soil under vibratory loads. The effect of quarry blasts, earthquakes and
nuclear explosions on structures is greatly influenced by the soil medium through which the shock waves.
traverse. In those parts of the world which experience freezing temperatures, problems arise because the
soils expand upon freezing and exert a force on the structures in contact with them. Thawing (due to
melting ice) of the soil results in a loss of strength in the soil. Structures resting on these soils will perform
satisfactorily only if measures are taken to prevent frost-heave or designed to withstand the effects of freezing
and thawing.

1.3 COMPLEXITY OF SOIL NATURE

A natural soil deposit is quite unlike any other material of construction known to man, Most of the commonly
used materials of construction such as wood, steel, concrete or reinforced concrete are capable of proper
structural analysis once a few simple and well chosen physical and mechanical parameters like the modulus
of elasticity, yield stress, Poisson's ratio, etc., are known, One can select the material which best meets the
prevailing conditions and then determine the allowable stress for that material. The material can be expected
to behave in a reasonably predictable manner. On the other hand, no choice of soil is normally available to an
engineer. Most of the suitable sites for construction have already been used up and often one has to make do
with a site having unsatisfactory subsoil conditions. Occasionally, it may be possible to improve the soil by
some suitable treatment, but more often than not, the soil has to be accepted in its natural state. Unlike a
manufactured material like steel, soil deposits have been placed by nature under a variety of conditions which
have rendered the deposits anything but homogencous. The wide range of characteristics that different soil
‘deposits from peats to compact gravels exhibit, is simply amazing. There is more. Even ata given site, samples
Of soil taken from two locations not too far apart, from the same stratum, may show widely varying properties.
It requires great ingenuity, therefore, to select representative soil parameters for a natural soil deposit.
Unexpected changes take place in soils when certain environmental changes occur. For instance, vibrations
can alter the state of a sand deposit from loose to dense. Some clay soils, which are extremely hard when dry,