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 NEW AGE INTERNATIONAL (P) LIMITED, PUBLISHERS 4835/24, Ansari Road, Daryaganj, ‘New Delhi - 110 002 Visit us at : www newagepublishers.com Offices at : Bangalore, Chennai, Cochin, Guwahati, Hyderabad, Jalandhar, Kolkata, Lucknow, Mumbai and Ranchi ‘This book or any part thereof may not be reproduced in any form without the written permission of the publisher. book cannot be sold outside the country to which it is consigned by the publisher without the prior permission of the publisher. Rs, 275.00 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 Bra yniiqaiee bre velqenae ling 2b [Ta egaitod bre 21 init Yo noitiengeiG bau dm! 2.1 Tfo noitemiqxd to riged Cet LW baud #eL Fd enoitarraedO » 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,