Fundamentals of Geotechnical Engineering This page intentionally left blank Fundamentals of Geotechnical Engineering THIRD EDITION Braja M. Das Australia Canada Mexico Singapore Spain United.Kingdom United.States Fundamentals of Geotechnical Engineering, Third Edition by Braja M. Das Publisher: Proofreader: Cover Design: Chris Carson Martha McMaster Andrew Adams Developmental Editor: Indexer: Compositor: Hilda Gowans Braja Das Integra Permissions Coordinator: Production Manager: Kristiina Bowering Renate McCloy Production Services: Creative Director: Cover Image Credit: RPK Editorial Services Angela Cluer Courtesy of Geopier Foundation Company, Inc., www.geopier.com Copy Editor: Interior Design: Shelly Gerger-Knechtl Carmela Pereira ALL RIGHTS RESERVED. No part of this work covered by the copyright herein may be reproduced, tran- scribed, or used in any form or by any Printed and bound in the United means—graphic, electronic, or me- States chanical, including photocopying, 1 2 3 4 07 recording, taping, Web distribution, or information storage and retrieval sys- tems—without the written permission of the publisher. For permission to use material from this text or product, submit a request online Every effort has been made to trace Library Congress Control Number: ownership of all copyright material 2007939898 and to secure permission from copy- right holders. In the event of any ISBN-10: 0-495-29572-8 question arising as to the use of any ISBN-13: 978-0-495-29572-3 material, we will be pleased to make the necessary corrections in future printings. Spain Paraninfo Calle/Magallanes, 25 28015 Madrid, Spain To our granddaughter, Elizabeth Madison This page intentionally left blank Preface Principles of Foundation Engineering and Principles of Geotechnical Engineering were originally published in 1984 and 1985, respectively. These texts were well received by instructors, students, and practitioners alike. Depending on the needs of the users, the texts were revised and are presently in their sixth editions. Toward the latter part of 1998, there were several requests to prepare a single volume that was concise in nature but combined the essential components of Principles of Foundation EngineeringandPrinciples of Geotechnical Engineering. In response to those requests, the first edition of Fundamentals of Geotechnical Engineering was published in 2000, followed by the second edition in 2004 with a 2005 copyright. These editions include the fundamental concepts of soil mechanics as well as foundation engineering, including bearing capacity and settlement of shallow foundations (spread footings and mats), retaining walls, braced cuts, piles, and drilled shafts. This third edition has been revised and prepared based on comments received from the users. As in the previous editions, SI units are used throughout the text. This edition consists of 14 chapters. The major changes from the second edition include the following: • The majority of example problems and homework problems are new. • Chapter 2 on “Soil Deposits and Grain-Size Analysis” has an expanded discus- sion on residual soil, alluvial soil, lacustrine deposits, glacial deposits, aeolian deposits, and organic soil. • Chapter 3 on “Weight-Volume Relationships, Plasticity, and Soil Classification” includes recently published relationships for maximum and minimum void ratios as they relate to the estimation of relative density of granular soils. The fall cone method to determine liquid and plastic limits has been added. • Recently published empirical relationships to estimate the maximum unit weight and optimum moisture content of granular and cohesive soils are included in Chapter 4 on “Soil Compaction.” • Procedures to estimate the hydraulic conductivity of granular soil using the results of grain-size analysis via the Kozeny-Carman equation are provided in Chapter 5, “Hydraulic Conductivity and Seepage.” vii viii Preface • Chapter 6 on “Stresses in a Soil Mass” has new sections on Westergaard’s solu- tion for vertical stress due to point load, line load of finite length, and rectangu- larly loaded area. • Additional correlations for the degree of consolidation, time factor, and coeffi- cient of secondary consolidation are provided in Chapter 7 on “Consolidation.” • Chapter 8 on “Shear Strength of Soil” has extended discussions on sensitivity, thixotropy, and anisotropy of clays. • Spencer’s solution for stability of simple slopes with steady-state seepage has been added in Chapter 9 on “Slope Stability.” • Recently developed correlations between relative density and corrected stan- dard penetration number, as well as angle of friction and cone penetration resistance have been included in Chapter 10 on “Subsurface Exploration.” • Chapter 11 on “Lateral Earth Pressure” now has graphs and tables required to estimate passive earth pressure using the solution of Caquot and Kerisel. • Elastic settlement calculation for shallow foundations on granular soil using the strain-influence factor has been incorporated into Chapter 12 on “Shallow Foundations––Bearing Capacity and Settlement.” • Design procedures for mechanically stabilized earth retaining walls is included in Chapter 12 on “Retaining Walls and Braced Cuts.” It is important to emphasize the difference between soil mechanics and founda- tion engineering in the classroom. Soil mechanics is the branch of engineering that involves the study of the properties of soils and their behavior under stresses and strains under idealized conditions. Foundation engineering applies the principles of soil mechanics and geology in the plan, design, and construction of foundations for build- ings, highways, dams, and so forth. Approximations and deviations from idealized con- ditions of soil mechanics become necessary for proper foundation design because, in most cases, natural soil deposits are not homogeneous. However, if a structure is to function properly, these approximations can be made only by an engineer who has a good background in soil mechanics. This book provides that background. Fundamentals of Geotechnical Engineering is abundantly illustrated to help students understand the material. Several examples are included in each chapter. At the end of each chapter, problems are provided for homework assignment, and they are all in SI units. My wife, Janice, has been a constant source of inspiration and help in com- pleting the project. I would also like to thank Christopher Carson, General Manager, and Hilda Gowans, Senior Development Editor, of Thomson Engineering for their encouragement, help, and understanding throughout the preparation and publica- tion of the manuscript. BRAJAM. DAS Henderson, Nevada Contents 1 Geotechnical Engineering—A Historical Perspective 1 1.1 Geotechnical Engineering Prior to the 18thCentury 1 1.2 Preclassical Period of Soil Mechanics (1700–1776) 4 1.3 Classical Soil Mechanics—Phase I (1776–1856) 5 1.4 Classical Soil Mechanics—Phase II (1856–1910) 5 1.5 Modern Soil Mechanics (1910–1927) 6 1.6 Geotechnical Engineering after 1927 7 References 11 2 Soil Deposits and Grain-Size Analysis 13 2.1 Natural Soil Deposits-General 13 2.2 Residual Soil 14 2.3 Gravity Transported Soil 14 2.4 Alluvial Deposits 14 2.5 Lacustrine Deposits 16 2.6 Glacial Deposits 17 2.7 Aeolian Soil Deposits 17 2.8 Organic Soil 18 2.9 Soil-Particle Size 19 2.10 Clay Minerals 20 2.11 Specific Gravity (G) 23 s 2.12 Mechanical Analysis of Soil 24 2.13 Effective Size, Uniformity Coefficient, and Coefficient of Gradation 32 Problems 35 References 37 ix