Laurence D. Wesley

GeotechnicalEngineeringin Residual Soils

Geotechnical E

ngineeringin R

esidual S

oils

WesleyTECHNOLOGY/ENGINEERING/CIVIL

The pioneering guide that breaks ground on the unique engineering properties of residual soilsGeotechnical Engineering in Residual Soils digs deep to help enrich the reader’s knowledge

on the subject of soils—in particular, residual soils—as they pertain to engineering. Appear-

ing mostly in underdeveloped parts of the United States and tropical countries, these soils

are playing an increasingly important role in building designs as construction encroaches

into these areas. In recognition of this fact, this guide equips geotechnical engineers with

essentials for learning the concepts and principles of residual soil behavior—and serves

as a starting point to assist them in pursuing innovative engineering strategies for working

effectively with residual soils. Geotechnical Engineering in Residual Soils:

• Introduces geotechnical engineers to those aspects of residual soil behavior that

they ought to be aware of when undertaking projects in these soils

• Highlights the mistaken interpretations of soil behavior that can result from the

application to residual soils of traditional concepts derived from sedimentary soils

• Includes numerous illustrations throughout, specifi cally addressing the unique

properties of residual soils

• Includes coverage of special topics, such as the role of negative pore pressure

above the water table, the infl uence of weather conditions on soil behavior, the

properties of volcanic soils, and compaction of residual soils

• Is written by an author with more than thirty years of fi rsthand experience

analyzing and designing for construction on residual soils

Thorough and insightful, Geotechnical Engineering in Residual Soils delivers a fresh over-

view on understanding the structural and mechanical properties of soils from an engi-

neering perspective—and informs readers how to solidify design approaches to set their

projects on a sure footing.

LAURENCE D. WESLEY worked as a practicing geotechnical engineer for more than

thirty years, with experience in New Zealand, Australia, Indonesia, Malaysia, and Bahrain.

He is a Lifetime Member of the American Society of Civil Engineers, and a retired senior

lecturer in geotechnical engineering at the University of Auckland.

Cover Art © Istockphoto.com/Alejandro Raymond | Cover Design: Holly Wittenberg

GEOTECHNICALENGINEERING INRESIDUAL SOILS

GEOTECHNICALENGINEERING INRESIDUAL SOILS

Laurence D. Wesley

JOHN WILEY & SONS, INC.

This book is printed on acid-free paper.

Copyright © 2010 by John Wiley & Sons, Inc. All rights reserved

Published by John Wiley & Sons, Inc., Hoboken, New Jersey

Published simultaneously in Canada

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Library of Congress Cataloging-in-Publication Data:Wesley, Laurence D.

Geotechnical engineering in residual soils / Laurence D. Wesley.p. cm.

Summary: “Wiley has long held a pre-eminent position as a publisher of books on geotechnicalengineering, with a particular strength in soil behavior and soil mechanics, at both the academic andprofessional level. This reference will be the first book focused entirely on the unique engineeringproperties of residual soil. Given the predominance of residual soils in the under-developed parts ofthe United States and the Southern Hemisphere, and the increasing rate of new construction in theseregions, the understanding of residual soils is expected to increase in importance in the comingyears. This book will be written for the practicing geotechnical engineer working to any degree withresidual soils. It will describe the unique properties of residual soil and provide innovative designtechniques for building on it safely. The author will draw on his 30 years of practical experienceas a practicing geotechnical engineer, imbuing the work with real world examples and practiceproblems influenced by his work in South America and Southeast Asia”—Provided by publisher.

Includes bibliographical references and index.ISBN 978-0-470-37627-0 (acid-free paper); ISBN 978-0-470-64436-2 (ebk); ISBN

978-0-470-64437-9 (ebk); ISBN 978-0-470-64438-6 (ebk)1. Residual materials (Geology) 2. Engineering geology. I. Title.TA709.5.W475 2010624.1′51–dc22

2010016879

Printed in the United States of America

10 9 8 7 6 5 4 3 2 1

CONTENTS

PREFACE AND ACKNOWLEDGMENTS xiii

1 FUNDAMENTAL ASPECTS OF RESIDUAL SOIL BEHAVIOR 1

1.1 Introduction / 11.2 Formation Processes and Basic Difference between Residual

and Sedimentary Soils / 21.3 Structure of Residual Soils / 51.4 Special Clay Minerals / 71.5 The Influence of Topography / 81.6 Geotechnical Analysis, Design, and the Role of Observation

and Judgment / 91.7 Summary of Basic Differences between Residual

and Sedimentary Soils / 11References / 12

2 EVALUATION, CHARACTERIZATION, AND CLASSIFICATIONOF RESIDUAL SOILS 13

2.1 Introduction / 132.2 Parent Rock and the Soil Profile / 132.3 Influence of Parent Rock on Geotechnical Properties / 152.4 The Role of Observation / 162.5 Standard Index Tests / 17

2.5.1 Particle Size / 182.5.2 Atterberg Limits / 19

v

vi CONTENTS

2.5.3 “Compactness” Indexes / 202.6 Classification Systems for Residual Soils / 21

2.6.1 Introduction / 212.6.2 Methods Based on Pedological Groups / 222.6.3 Methods Intended for Specific Local Use / 242.6.4 A Grouping System Based on Mineralogy

and Structure / 24References / 33

3 PORE PRESSURES AND SEEPAGE CONDITIONS ABOVEAND BELOW THE WATER TABLE 35

3.1 Introduction / 353.2 Situation at Level Sites / 36

3.2.1 Static Case / 363.2.2 Seasonal Effects / 373.2.3 Coarse-Grained Soils / 373.2.4 Low-Permeability Clays / 373.2.5 Medium- to High-Permeability Clays / 393.2.6 Use of Terzaghi Consolidation Theory to Illustrate

Seasonal Influence / 403.2.7 Field Records of Seasonal Effects / 42

3.3 Hill Slopes, Seepage, and Pore Pressures / 443.4 Permeability of Residual Soils / 473.5 Significance of the Water Table (or Phreatic Surface) / 483.6 Implications of the Groundwater and Seepage State above the

Water Table for Practical Situations / 483.6.1 Errors in the Estimation of Foundation Settlement

Using Conventional Methods / 483.6.2 Ground Settlement Resulting from Groundwater

Lowering / 493.6.3 Ground Settlement or Swelling Due to Covering the

Ground Surface / 503.6.4 Errors in Estimates of Slope Stability Ignoring Soil

Suction Influence / 513.6.5 Errors in Estimates of Slope Stability because of

Simplified Assumptions Regarding the SeepagePattern in the Slope / 51

References / 51

CONTENTS vii

4 CONSOLIDATION AND SETTLEMENT 53

4.1 Introduction / 534.2 Interpretation of Standard Oedometer Test Results

and the “Omnipotence of Tradition” / 544.3 Behavior of Residual Soils / 57

4.3.1 Tropical Red Clay / 574.3.2 Piedmont Residual Soil / 584.3.3 Waitemata Residual Clay / 604.3.4 Volcanic Ash (Allophane) Soils / 624.3.5 Summary of Principal Aspects of Compression

Behavior of Residual Soils / 634.4 Consolidation Behavior after Remolding / 654.5 Values of Stiffness Parameters for Residual Soils / 674.6 Time Rate and Estimation of the Coefficient of

Consolidation / 674.7 Rate of Consolidation for Surface Foundations on Deep Soil

Layers / 734.8 Examples of Settlement Estimates / 76

4.8.1 Foundations for a Multistory Building on RedClay / 76

4.8.2 Settlement Estimate Involving NonlinearCompressibility and Pore Pressure Influence / 82

4.8.3 Significance of Time Rate Assumption in thePrevious Example / 95

4.9 Accuracy of Settlement Estimates Based on OedometerTests / 964.9.1 A Common Source of Error Arising from the Use

of the Log Parameter (Cs) / 964.9.2 Actual Settlement versus Predictions / 98

4.10 Allowable Differential Settlement for Surface Foundationson Residual Soil / 98

References / 99

5 SHEAR STRENGTH OF RESIDUAL SOILS 101

5.1 Introduction / 1015.2 Undrained Shear Strength / 1025.3 Effective Strength Properties / 103

viii CONTENTS

5.3.1 Influence of Discontinuities / 1045.3.2 Correlation between φ′ Value and the Atterberg

Limits / 1055.3.3 Effective Strength Parameters of a Residual Soil

Derived from Shale / 1065.3.4 Stress–Strain Behavior in Triaxial Tests / 1075.3.5 The Cohesion Intercept c′ / 1075.3.6 Residual Strength / 112

References / 114

6 SITE INVESTIGATIONS AND THE MEASUREMENTOF SOIL PROPERTIES 115

6.1 Introduction / 1156.2 Approaches to Site Investigations / 1166.3 Organizational and Administrative Arrangements / 1166.4 Planning Site Investigations / 1186.5 Field Work / 119

6.5.1 Hand Auger Boreholes / 1196.5.2 Machine Boreholes / 1206.5.3 Penetrometer Testing / 121

6.6 Block Sampling / 1226.7 In Situ Shear Tests / 1246.8 Laboratory Testing / 126

6.8.1 Index or Classification Tests / 1266.8.2 Tests on Undisturbed Samples / 1266.8.3 “Computer Errors” in Processing Laboratory Test

Results / 1286.9 Correlations with Other Properties and Parameters / 129

6.9.1 Undrained Shear Strength / 1306.9.2 Relative Density of Sand / 132

References / 133

7 BEARING CAPACITY AND EARTH PRESSURES 135

7.1 Introduction / 1357.2 Bearing Capacity and Foundation Design / 1367.3 Earth Pressure and Retaining Wall Design / 139

7.3.1 Earth Pressure to Retain Cuts in Steep Slopes / 1397.3.2 The Use of Residual Soils for Reinforced Earth

Construction / 146References / 150

CONTENTS ix

8 SLOPE STABILITY AND SLOPE ENGINEERING 151

8.1 Introduction / 1518.2 Failure Modes / 1528.3 The Place of Analytical and Nonanalytical Methods for

Assessing the Stability of Natural Slopes / 1528.4 Application and Limitations of Analytical Methods / 1548.5 Uncertainties in Material Properties / 154

8.5.1 Slopes Consisting of Uniform, HomogeneousMaterials / 154

8.5.2 Slopes Containing Distinct, Continuous Planes ofWeakness / 155

8.5.3 Slopes of Heterogeneous Material, but withoutDistinct Planes of Weakness / 156

8.6 Uncertainties in the Seepage and Pore Pressure State / 1568.6.1 Influence of Climate and Weather / 1568.6.2 Response of Seepage State and Pore Pressure to

Rainfall / 1578.6.3 Comparison with Sedimentary Soils / 159

8.7 The Worst-Case Assumption Regarding the Water Table / 1598.8 Transient Analysis of Rainfall Influence on the Stability

of a Homogeneous Clay Slope / 1648.9 Modeling Stability Changes Resulting from Varying Rainfall

Intensities / 1698.10 The Hong Kong Situation / 172

8.10.1 Measurements of Pore Pressure Response / 1738.10.2 The Wetting Front Method for Estimating Water

Table Rise / 1768.10.3 Importance of Antecedent Rainfall / 1778.10.4 Results of Stability Analysis and Assumptions

Regarding the Pore Pressure State / 1778.10.5 Recommended Safety Factors for Hong Kong

Slopes / 1788.10.6 Triaxial Tests and Back-Analysis of

Landslides / 1788.10.7 Concluding Remarks on the Hong Kong

Situation / 1798.11 Back-Analysis Methods to Determine Soil Parameters / 180

8.11.1 Back-Analysis of a Single Slip or a Single IntactSlope / 180

x CONTENTS

8.11.2 Analysis of a Number of Slips in the SameMaterial / 181

8.11.3 Analysis of a Large Number of Intact Slopes (NoPrevious Slips) / 183

8.12 Slope Design / 1848.12.1 Selection of the Profile for a New Cut Slope / 1848.12.2 To Bench or Not to Bench a Slope? / 1868.12.3 A Note on Vegetation Cover on Slopes / 187

References / 187

9 VOLCANIC SOILS 189

9.1 Introduction and General Observations / 1899.2 Allophane Clays / 189

9.2.1 Performance of Natural Hill and MountainSlopes / 190

9.2.2 Formation of Allophane Clays / 1909.2.3 Structure of Allophane Clays / 1929.2.4 Particle Size / 1939.2.5 Natural Water Content, Void Ratio, and Atterberg

Limits / 1939.2.6 Influence of Drying / 1949.2.7 Degree of Saturation, Liquidity Index, and

Sensitivity / 1959.2.8 Identification of Allophane Clays / 1979.2.9 Compressibility and Consolidation

Characteristics / 1979.2.10 Strength Characteristics / 2009.2.11 Compaction Behavior / 2039.2.12 Engineering Projects Involving Allophane

Clays / 2059.3 Volcanic Ash Clays Derived from Rhyolitic Parent

Material / 2059.4 Other Unusual Clays of Volcanic Origin / 2109.5 Pumiceous Materials / 213

9.5.1 Pumice Sands / 2139.5.2 Pumiceous Silts and Gravels / 217

References / 221

CONTENTS xi

10 RESIDUAL SOILS NOT DERIVEDFROM VOLCANIC MATERIAL 223

10.1 Introduction / 22310.2 Weathered Granite (Group 1 in Figure 10.1) / 22310.3 Weathered Sedimentary Rocks / 226

10.3.1 Soft Rocks—Sandstones, Mudstones, and Shale(Group 3 in Figure 10.1) / 226

10.3.2 Hard Sedimentary Rocks (Group 4 inFigure 10.1) / 227

10.4 Laterites and Tropical Red Clays (Group 5 inFigure 10.1) / 228

10.5 Black or Black Cotton Clays / 230References / 232

11 COMPACTION OF RESIDUAL SOILS 233

11.1 Introduction / 23311.2 Some Reflections on Compaction Behavior of Soils and

Quality Control Methods / 23511.3 Optimum Compactive Effort as well as Optimum Water

Content / 23611.4 Alternative Compaction Control Based on Undrained Shear

Strength and Air Voids / 23711.5 The Use of Shear Strength to Overcome Difficulties in

Compacting Residual Soils / 24111.5.1 Soils That Contain Wide and Random Variations in

Properties / 24111.5.2 Nonsensitive Soils Considerably Wetter than

Optimum Water Content / 24111.5.3 Sensitive, Highly Structured Soils / 242

11.6 Hard, Partially Weathered, Residual Soils / 243References / 243

INDEX 245

PREFACE AND ACKNOWLEDGMENTS

This book is, in many ways, an addendum, or an appendix to my earlier bookFundamentals of Soil Mechanics for Sedimentary and Residual Soils. Therewere a number of things I wanted to say about geotechnical engineeringin residual soils that would have been out of place in that book, so aseparate book seemed the most appropriate place for saying them. Thisbook should perhaps also have had a subtitle and been called: GeotechnicalEngineering in Residual Soils—A Personal View, because it does tend to bethat. However, I have attempted to produce a stand-alone book and to makeit reasonably balanced in terms of its coverage of all residual soil types.This means there is considerable overlap with the content of my earlierbook. The book is intended primarily for those who are already familiarwith the subject of soil mechanics and have some experience of practicalgeotechnical engineering, but not a lot of knowledge of residual soils. Atthe same time I hope it will also be of value to those already familiar withresidual soils.

The story behind Fundamentals of Soil Mechanics for Sedimentary andResidual Soils and this book is a long one, and (at the risk of boring thereader), I will recount it briefly. Along the way I will acknowledge myindebtedness to several specific organizations, institutions, and individualswho have had an important association with the history of the two books.

The story starts with my participation in a program known as the Volun-teer Graduate Scheme, which was organized by the New Zealand UniversityStudents’ Association in the late 1950s, with the support of both the NewZealand and Indonesian governments. That scheme was a copy of the Aus-tralian Volunteer Graduate Scheme, which started in the early 1950s, andboth were forerunners to such schemes as the United States’ Peace Corps,and the United Kingdom’s Volunteer Service Overseas. Under the auspices

xiii