Foundation Engineering P.C. Varghese
Foundation Engineering P.C. VARGHESE Honorary Professor, Anna University, Madras Formerly, Professor and Head, Department of Civil Engineering Indian Institute of Technology Madras, Chennai, and UNESCO Chief Technical Advisor, University of Moratuwa, Sri Lanka New Delhi 110001 2012
FOUNDATION ENGINEERING P.C. Varghese 2005 by PHI Learning Private Limited, New Delhi. All rights reserved. No part of this book may be reproduced in any form, by mimeograph or any other means, without permission in writing from the publisher. ISBN-978-81-203-2652-1 The export rights of this book are vested solely with the publisher. Ninth Printing May, 2012 Published by Asoke K. Ghosh, PHI Learning Private Limited, M-97, Connaught Circus, New Delhi-110001 and Printed by Mudrak, 30-A, Patparganj, Delhi-110091.
To Professor Arthur Casagrande under whose guidance the author started his studies in Geotechnical Engineering
1 Contents Preface Acknowledgements Introduction Units xv xvii xix xxi Chapter 1 Engineering Properties of Soils 1 36 1.1 Introduction 1 1.2 Models Used in Design of Foundations 1 1.3 Important Engineering Properties 2 1.4 Review of Physical Properties 3 1.5 Strength of Soils 10 1.6 Soil Parameters from Field Sounding Tests 12 1.7 Dynamic Penetration Tests 13 1.8 Static Cone Penetration Test (SCPT) (q c ) 18 1.9 Correlation between SCPT and SPT 20 1.10 In-situ Vane Shear Test 21 1.11 Estimation of Modulus of Subgrade Reaction and Modulus of Elasticity 22 1.12 Consolidation Properties of Clays 30 1.13 Settlement of Overconsolidated Clays 32 References 35 Chapter 2 Contact Pressures on Base of Footings 37 47 2.1 Introduction 37 2.2 Rigid and Flexible Foundations 37 2.3 Contact Pressures under Rigid and Flexible Footings 38 2.4 Concept of Modulus of Subgrade Reaction 39 2.5 Concept of Bulb of Pressure 40 2.6 Effect of Rigidity on Settlement Calculations 40 v
vi Contents 2.7 Assumptions for Proportioning of Rigid Footings 41 2.8 Structural Design of Footings 44 References 47 Chapter 3 Stress Distribution in Soils 48 68 3.1 Introduction 48 3.2 Soil Considered as an Elastic Material 48 3.3 Boussinesq s Equation 48 3.4 Application of Boussinesq s Formula to Other Cases 50 3.5 Westergard s Solution [IS 8009 (Part I) 1976] 57 3.6 Methods for Special Cases 58 3.7 Stress Distribution for Load Applied Below the Surface 59 3.8 Pressure Distribution at Base of Strip Footings 59 3.9 Heave in Clay due to Excavation 60 3.10 Stresses on Retaining Walls due to Loads Behind the Walls 61 3.11 Approximate Methods for Evaluation of Vertical Stresses in Soils 62 3.12 Distribution of Load of a Single Pile 64 3.13 Selection of Method for Use 64 3.14 Summary 65 References 68 Chapter 4 Settlement of Foundations 69 98 4.1 Introduction 69 4.2 Elastic Settlement of Footings 69 4.3 Settlement of Foundation on Cohesionless Soil 73 4.4 Estimation of Total Settlement of Foundations on Cohesive Soils 77 4.5 Secondary Consolidation 80 4.6 Determination of Rate of Settlement 81 4.7 Estimation of Differential Settlement 82 4.8 Settlement of a Group of Piles Used as Foundation (Deep Foundations) 82 4.9 Settlement of Pier Foundations 83 4.10 Allowable Differential Settlements 83 4.11 Methods to Reduce Settlement in Buildings 85 4.12 Rotation of Footings Subjected to Moments 85 4.13 Summary 87 References 98 Chapter 5 General Requirements of Shallow and Deep Foundations 99 108 5.1 Introduction 99 5.2 Depth of Foundations 100 5.3 Importance of Soil Immediately Below Foundation Shallow 101 5.4 Standard Practice of Laying Footing Foundation of Buildings 102 5.5 Construction of Footings for Basements 103 5.6 Foundations on Fills 103
Contents vii 5.7 Foundations on Soft Deposits 103 5.8 Safe Bearing Capacity for Simple Cases 104 5.9 Reduction of Bearing Capacity with Submergence 104 5.10 Types of Foundations and Their Uses 104 References 108 Chapter 6 Bearing Capacity of Shallow Foundations 109 133 6.1 Introduction 109 6.2 Some Definitions 109 6.3 Terzaghi s Theory 110 6.4 Bearing Capacity Factors 113 6.5 Bearing Capacity of Shallow Footings in Clays 115 6.6 Effect of Water Table on Ultimate Bearing Capacity 116 6.7 Allowable Bearing Capacity 117 6.8 Settlement of Footings in Sand Deposits from SPT Values 117 6.9 Safe Bearing Capacity in Clays 123 6.10 General Remarks 123 6.11 Bearing Capacity of Stratified Soils 124 6.12 Precautions To Be Taken in Foundation Preparation for Footings 125 6.13 Load Tests for Bearing Capacity 125 6.14 Design Practice 125 6.15 Summary of Formulae for Bearing Capacity of Soils 126 References 132 Chapter 7 Factors Affecting Bearing Capacity of Shallow Foundations 134 149 7.1 Introduction 134 7.2 Major Factors Affecting Bearing Capacity 134 7.3 Effect of Size of Foundation 134 7.4 Effect of Shape, Depth and Inclination of Load on Bearing Capacity of Footings 135 7.5 Stability under Inclined Loads 137 7.6 Effect of Eccentricity of Load 139 7.7 Effect of Inclination of Base of Foundation 140 7.8 Effect of Footings on Sloping Ground 140 7.9 Effect of Shape of Base of Foundation 141 7.10 Footings on Stratified Soils 141 7.11 General Equations for Bearing Capacity 141 7.12 Summary 141 References 149 Chapter 8 Design of Raft Foundations 150 172 8.1 Introduction 150 8.2 Types of Rafts and Their Use 151 8.3 Loads on Rafts 152 8.4 Stiffness or Rigidity of Soil Structure System 152 8.5 Allowable Soil Pressures for Rafts in Cohesionless Soils 153
viii Contents 8.6 Allowable Pressures for Rafts in Cohesive Soils 154 8.7 Structural Design of Raft Foundations 156 8.8 Rigid Beam Analysis (Conventional Method) 158 8.9 Winkler Model Analysis 159 8.10 Solution as Plates or Beams on Elastic Half-space (Elastic Continuum) 161 8.11 Closed Form Solutions Based on Elastic Theory 162 8.12 ACI Methods for Analysis of Beams and Grids on Elastic Foundation 162 8.13 Raft-Superstructure Interaction 162 8.14 Tank Foundations 162 8.15 Summary 163 References 172 Chapter 9 Load Carrying Capacity of Piles by Static Formulae 173 209 9.1 Introduction 173 9.2 Types of Piles 173 9.3 Commonly Used Sizes Structural Capacity 174 9.4 Barrette Foundations 174 9.5 IS Codes on Piles 174 9.6 Factors Affecting Choice of Type of Pile 175 9.7 Load Carrying Capacity 176 9.8 Effective Length Point of Inflection 177 9.9 Historic Development of Static Method 177 9.10 Method 1 Static Formula (for Piles in Granular Soils) 180 9.11 Method 1 Static Formula (for Cohesive Soils) 183 9.12 Capacity of Piles in c f Soils By Static Formula 186 9.13 Factor of Safety for Static Formula Based on Soil Properties 186 9.14 Limiting Capacity of Piles 187 9.15 Method 2 Meyerhof s Formula for Driven Piles in Sand Based on SPT Values 187 9.16 Method 3 Load Carrying Capacity From Static Cone Penetration Tests 189 9.17 Negative Skin Friction 191 9.18 Comparison of Capacities of Driven and Bored Piles 193 9.19 Capacity of Piles Founded on Solid Rock 193 9.20 Socketing of Bored Piles in Weathered and Soft Rock 194 9.21 Buckling of Slender Piles 197 9.22 Uplift Resistance (Tension Capacity) of Piles 197 9.23 Tapered Piles 198 9.24 Bearing Areas of Driven Hollow and H Piles 199 9.25 Summary 199 References 208 Chapter 10 Load Carrying Capacity of Piles by Dynamic Formulae 210 237 10.1 Introduction 210 10.2 Pile Driving Formulae 211 10.3 Determination of Temporary Elastic Compression During Driving 215 10.4 Selection of Pile Hammers 216 10.5 Driving Stresses in Piles 217
Contents ix 10.6 Jetting of Pre-cast Piles 218 10.7 Examination of Suitability of Hammer for Driving 218 10.8 Lifting and Pitching of Piles 218 10.9 Field Measurement of Set of Piles 219 10.10 Field Record of Pile Driving 221 10.11 Other Pile Driving Formulae 221 10.12 Wave Equation Analysis of Piles [WAP] 222 10.13 Tension Cracking of Piles During Driving 227 10.14 Summary 228 References 236 Chapter 11 Structural Design of Concrete Piles 238 252 11.1 Introduction 238 11.2 Cover To Be Used 238 11.3 Requirements of Concrete for Pile Works 238 11.4 Detailing of Steel in Cast In-situ Piles 239 11.5 Detailing of Longitudinal Steel in Pre-cast Piles 240 11.6 Links in Pre-cast Driven Piles (IS 2911 Part I Sec. 3) 241 11.7 Pre-stressed Concrete Piles 241 11.8 Pile Shoes 244 11.9 Pile to Pile Cap Connections 246 11.10 Design of Pile Caps 248 11.11 Deterioration of Concrete and Corrosion of Steel in Piles 248 11.12 Summary 248 References 252 Chapter 12 Construction of Cast in-situ Piles 253 259 12.1 Introduction 253 12.2 Construction of Driven Cast in-place Piles 253 12.3 Bored Cast in-situ Piles 254 12.4 Properties of Bentonite To Be Used 254 12.5 Methods of Advancing the Hole 256 12.6 Choice of Tools 257 12.7 Limitations of Bentonite Method 258 12.8 Action To Be Taken Before Concreting 258 12.9 Concreting of Piles 258 12.10 Summary 259 Reference 259 Chapter 13 Group Action and Lateral Resistance of Vertical Piles 260 284 13.1 Introduction 260 13.2 Minimum Spacing of Piles 260 13.3 Estimation of Group Bearing Capacity 260 13.4 Effect of Pile Arrangement 262 13.5 General Analysis of Pile Groups 262
x Contents 13.6 Lateral Resistance of Single Pile 264 13.7 IS 2911 Method for Lateral Resistance of Piles 266 13.8 Broms Charts for Lateral Load Analysis on Single Piles 271 13.9 Analysis of Lateral Loads on Piles Using Finite Element Method 276 13.10 Improving Lateral Resistance of Piles 276 13.11 Summary 276 References 283 Chapter 14 Field Tests on Piles 285 294 14.1 Introduction 285 14.2 Types of Load Tests on Piles 286 14.3 Loading Arrangements for Vertical Load Test 286 14.4 Types of Vertical Load Tests on a Single Pile 287 14.5 Vertical Load Test on Pile Group 290 14.6 Nondestructive Tests (NDTs) on Piles 290 14.7 Other Field Tests on Piles 291 References 293 Chapter 15 Piled Raft Foundations 295 300 15.1 Introduction 295 15.2 Types of Piled Rafts 296 15.3 Transfer of Load to Piles in a Piled Raft 297 15.4 Design of Piled Raft for Settlement Reduction (Type 1 Piled Rafts) 297 15.5 Approximate Design of Piled Raft for Load Transmission [Type 2 Piled Rafts] 299 15.6 Effect of Various Parameters on Results of Analysis 299 References 300 Chapter 16 Lateral Earth Pressures on Rigid Walls 301 319 16.1 Introduction 301 16.2 Historical Development 301 16.3 Nature and Magnitudes of Earth Pressures 302 16.4 Pressures on Retaining Structures 304 16.5 Coulomb s Theory of Earth Pressure 305 16.6 Culmann s Graphical Construction for Active Pressure 309 16.7 Plastic Equilibrium of Soils Active and Passive Rankine States 311 16.8 Effect of Submergence and Broken Back 312 16.9 Pressures Due to Soils with Cohesion 313 16.10 Economical Design of High Retaining Walls 315 References 319 Chapter 17 Effect of Superimposed Loads on Backfill and Empirical Design of Retaining Walls 320 333 17.1 Introduction 320 17.2 Case 1: Effect of Uniform Surcharge (q/m 2 ) 320
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