DESIGN OF PILE FOUNDATIONS IN LIQUEFIABLE SOILS

Transcription

1 DESIGN OF PILE FOUNDATIONS IN LIQUEFIABLE SOILS

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3 DESIGN OF PILE FOUNDATIONS IN LIQUEFIABLE SOILS Gopal Madabhushi University of Cambridge, UK Jonathan Knappett University of Dundee, UK Stuart Haigh University of Cambridge, UK ICP Imperial College Press

4 Published by Imperial College Press 57 Shelton Street Covent Garden London WC2H 9HE Distributed by World Scientific Publishing Co. Pte. Ltd. 5 Toh Tuck Link, Singapore USA office: 27 Warren Street, Suite , Hackensack, NJ UK office: 57 Shelton Street, Covent Garden, London WC2H 9HE British Library Cataloguing-in-Publication Data A catalogue record for this book is available from the British Library. DESIGN OF PILE FOUNDATIONS IN LIQUEFIABLE SOILS Copyright 2010 by Imperial College Press All rights reserved. This book, or parts thereof, may not be reproduced in any form or by any means, electronic or mechanical, including photocopying, recording or any information storage and retrieval system now known or to be invented, without written permission from the Publisher. For photocopying of material in this volume, please pay a copying fee through the Copyright Clearance Center, Inc., 222 Rosewood Drive, Danvers, MA 01923, USA. In this case permission to photocopy is not required from the publisher. ISBN ISBN Printed in Singapore.

5 From Gopal Madabhushi: To my parents for allowing me to pursue what I wanted and to Raji, Spandana and Srikanth for reminding me of the meaning of life. From Jonathan Knappett: To Lis, for the unwavering support you continue to give me and to my parents, for making me the person I am today. From Stuart Haigh: To Esra and Maya for their constant support and the joy they bring to my life.

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7 Foreword The Design of Pile Foundations in Liquefiable Soils provides a systematic evaluation of the effects of liquefaction on pile foundations and includes earthquake observations, research findings, and design principles and procedures from a variety of sources worldwide. The book provides a logical framework for understanding the basics of single pile and pile group design, liquefaction, and the effects of earthquake loading and liquefaction on the axial and lateral loads transmitted to pile foundations. It also provides a framework for understanding the effects that loss of bearing and lateral restraint in saturated sandy soils subject to cyclic loading have on the capacity of pile foundations. By combining earthquake loading in liquefiable soils with mechanisms that reduce pile capacity, the book develops a rational process for quantifying loads and capacity reduction into a design process. Pile response to earthquakes and liquefaction involves complex material behavior in terms of increased pore pressure and reduced soil strength and stiffness, complex mass behavior of the ground in terms of kinematic loading, complex performance of the superstructure in terms of inertial loads transmitted to the piles, and complex interaction between the soil and pile foundation. This book provides a valuable guide for students, researchers, and designers in navigating these complexities. Chapter 1 focuses on the performance of pile foundations with a review of factors contributing to axial pile capacity, performance-based design principles for piles subject to earthquakes, and the observed performance of pile foundations during previous earthquakes. Chapter 2 reviews inertial and kinematic loading, and presents the essentials of p-y analysis and limit equilibrium methods to estimate the maximum shear vii

8 viii Design of Pile Foundations in Liquefiable Soils and moment in piles in laterally spreading soils. Chapter 3 covers factors affecting the axial loading of piles in liquefiable soils, including reduction in end-bearing capacity due to elevated pore pressures and the potential for beam buckling associated with the loss of lateral restraint in liquefying soils. Chapter 4 focuses on lateral spreading in liquefied soils, including empirical methods for estimating lateral spread movement, soil-pile interaction in liquefied soil, and limiting lateral earth pressures for pile design. Chapter 5 evaluates combined axial and lateral pile loading effects in laterally spreading ground with a treatment of single pile and pile group behaviour and the use of interaction diagrams to analyse pile performance when multiple failure mechanisms are possible. Chapter 6 provides a substantial number of design examples to illustrate the design procedures developed in the book. The Design of Pile Foundations in Liquefiable Soils also demonstrates the importance of centrifuge testing to identify and quantify key failure mechanisms associated with complex soil-structure interaction. The combined use of careful field observations, centrifuge experiments and fundamental mechanics to develop analytical procedures and a structured design process is well illustrated by this book. The provision of design examples is a particularly attractive feature. The worked examples show explicitly how to apply the design process, and provide an indispensible link between theory and practice. The Design of Pile Foundations in Liquefiable Soils provides substantial forward progress in conceptualising and formalising the analytical and design treatment of the truly complex, and sometimes vexing, phenomena associated with pile response to earthquake loading and liquefaction. For those interested in liquefaction, liquefactioninduced soil-structure interaction, pile design, and centrifuge testing, this book will be a valuable and frequently used addition to their technical library. T.D. O Rourke Thomas R. Briggs Professor of Engineering School of Civil and Environmental Engineering Cornell University Ithaca, NY USA 12 April 2009

9 Preface Pile foundations are widely used both onshore and offshore to transfer superstructure loads into the ground. In seismic regions there is uncertainty regarding their performance, particularly when the soil strata that the piles pass through or bear on are susceptible to liquefaction. This book aims to clarify the mechanisms by which pile foundations may fail when the soil suffers liquefaction. In addition, the problem of down slope movement of nonliquefied ground that overlies liquefied layers and its effect on pile foundations is considered. One of the key factors to remember is that the pile foundations are often carrying substantial axial loads from the superstructure at the time of the earthquake. It is therefore imperative to consider the pile behaviour in liquefiable soils when they are subjected to both axial and lateral loads. This can have consequences for pile behaviour such as sudden and catastrophic buckling instability or excessive and unwarranted settlements. This book is organised into six chapters. It aims to marry the most recent research findings on pile behaviour to the needs of practical designs in seismic regions. Accordingly, it is intended to be used by graduate students and researchers interested in pile foundation design, as well as geotechnical practitioners faced with the problem of designing or assessing the seismic risk to existing pile foundations in regions with liquefiable soils. Chapter 1 introduces the static design of piles using traditional or CPT-based methods. It looks at the performance of piles in past earthquakes through some well-documented case studies. The concepts of performance design and the importance of estimating deformations of pile foundations are highlighted. ix

10 x Design of Pile Foundations in Liquefiable Soils Chapter 2 deals with the inertial and kinematic loads attracted by pile foundations during earthquake loading. These are considered initially for normal ground and later on in liquefiable soils. Limit equilibrium-based methods are introduced to estimate the loading due to laterally spreading nonliquefied layers. Chapter 3 introduces liquefaction as a foundation hazard and discusses how the consequent loss of soil strength influences the axial load that can be safely carried by pile foundations. Possible axial failure modes including liquefaction-induced bearing capacity failure and instability (buckling) are discussed in relation to the static considerations outlined in Chapter 1. Chapter 4 discusses the lateral spreading of sloping ground and the particular problems that arise when pile foundations pass through such laterally spreading ground. Recent research experiences are presented and compared with current codal provisions. Chapter 5 brings together the material in Chapters 2 to 4 in considering the design of pile foundations against combinations of transient seismic loads (Chapter 2), axial load (Chapter 3) and kinematic forces due to lateral spreading (Chapter 4). Chapter 6 presents a series of design examples to demonstrate how the methods outlined in Chapters 1 to 5 may be combined within an inclusive design method. Finally, the authors would like to thank Professor Tom D. O Rourke of Cornell University, USA and the 49 th Rankine Lecturer, for writing the foreword. Similarly the authors would like to acknowledge the help and support of many researchers at the Schofield Centre who shared in the enthusiasm of understanding the complex problems of soil liquefaction and earthquake geotechnical engineering. Particular mention must be made of the excellent support received from the technical staff during many an experimental project. In fact, it is the excellent research atmosphere at the Centre of freely sharing knowledge and technical know-how that makes work a pleasure and made this book possible.

11 Contents Foreword Preface 1. Performance of Pile Foundations Introduction Axial capacity of a single pile Pile capacity based on CPT testing Pile base capacity Shaft friction Performance of Pile Foundations During Earthquake Loading Soil Liquefaction and Lateral Spreading Performance of Pile Foundations in Past Earthquakes Showa bridge failure Niigata Family Court House building The Landing Bridge performance The Harbour Master s Tower at Kandla Port Modes of Pile Failure in Liquefiable Soils Failure mechanisms for single piles Failure mechanisms for pile groups Summary Inertial and Kinematic Loading Pile Behaviour Under Earthquake Loading Inertial loading Kinematic loading in level ground Kinematic loading in sloping ground Analysis of Laterally Loaded Piles Under Static Conditions Simplified soil profiles Simplified analysis procedures for piles under static loading Analysis of Laterally Loaded Piles Under Earthquake Loading vii ix xi

12 xii Design of Pile Foundations in Liquefiable Soils Variation in the action of inertial and kinematic loads with depth Effective lengths of piles Pile flexibility Kinematic Response in Level Ground Kinematic Loading in Laterally Spreading Soil Inertial Response Relative stiffness of pile-soil system Damping coefficients p-y Analysis of Piles Static lateral loading Cyclic lateral loading p-y analysis under earthquake loading level ground p-y analysis under earthquake loading sloping ground Limit Equilibrium Analysis of Piles Subjected to Earthquake Loading Limit equilibrium of piles in laterally spreading soils Limit equilibrium analysis in the presence of nonliquefied crust Stiff clay as a nonliquefiable layer Dense sand as a nonliquefiable layer Provisions in Eurocode Combination rules Pile head fixity coefficients Kinematic loading Summary Accounting for Axial Loading in Level Ground Liquefaction as a Foundation Hazard Liquefaction Determination of liquefaction susceptibility Influence of Axial Loading on Pile Failure Axial Load Transfer Due to Liquefaction Liquefaction-induced (co-seismic) Downdrag (post-earthquake) Pile Settlement Liquefaction-induced (co-seismic) Downdrag (post-earthquake) Guidelines for Designing Against Bearing Failure Instability of Single Piles and Pile Groups Rock-socketed piles Floating piles Bearing vs. Buckling Failure Methodology Sample analysis

13 Contents xiii Ultimate axial limiting states for piled foundations Use of limiting states in pile sizing Summary Lateral Spreading of Sloping Ground Liquefaction-induced Lateral Spreading Introduction Simple Methods to Estimate the Extent of Lateral Spreading Effects of Lateral Spreading on Pile Foundations Presence of nonliquefiable crust Lateral pressures generated on piles and pile caps Current codal provisions Specifications for Highway Bridges (JRA, 2002) Design Standard for Railway Facilities (RTRI 1999) Recommendations for Design of Building Foundations (AIJ 2001) Recent experimental data vs codal provisions Recommendations on Estimation of Lateral Loads for Pile Design Axial Loading on Piles in Laterally Spreading Ground Introduction Phasing of Loads Inertial and kinematic loads Presence of axial loads Peak Lateral Response of Piled Foundations Residual Lateral Response of Piled Foundations Single piles Pile groups (including axial load) Comparison of single pile and group pile behaviour Insight into effects of axial load on group response Validation of Effects of Axial Pile Load Recommendations for Designing Piles in Laterally Spreading Ground Design Examples Introduction Design of Piles Under Static Loading Example 1: Preliminary design of piles under static loading End bearing Shaft resistance Example 2: Preliminary design of piles using CPT data End bearing Shaft resistance

14 xiv Design of Pile Foundations in Liquefiable Soils 6.3 Inertial and Kinematic Loading on Piles in Level Ground Example 3: Soil stiffness and natural frequency Example 4: Effective length and flexibility of the pile Effective length of the pile Flexibility of the pile Example 5: Inertial loading on the pile Example 6: Kinematic interaction Design of Piles in Level Liquefiable Ground Example 7: Determination of liquefaction potential from CPT data Example 8: Pile sizing based on liquefaction considerations Example 9: Inertial response in level liquefied ground Design of Piles in Sloping Liquefiable Ground Example 10: Pile group in two-layer soil profile subject to lateral spreading Method Method Method Example 11: Pile group in three-layer soil profile subject to lateral spreading Summary of Inclusive Design Procedure References 203 Index 211