C580.pdf

1. Embedded retaining walls – guidance for economic design A R Gaba Ove Arup and Partners B Simpson Ove Arup and Partners W Powrie University of Southampton D R Beadman Ove Arup and Partners 6 Storey's Gate, Westminster, London SW1P 3AU TELEPHONE 020 7222 8891 FAX 020 7222 1708 EMAIL [email protected] WEBSITE www.ciria.org CIRIA C580 London 2003 2. Summary This book provides best practice guidance on the selection and design of vertical embedded retaining walls. It covers temporary and permanent cantilever, anchored, single and multi-propped retaining walls that are supported by embedment in stiff clay and other competent soils. The content addresses the technical and construction issues relating to the selection of appropriate wall type and construction sequence to achieve overall economy. It clarifies areas of design ambiguity and presents a clear, unambiguous method for the design of such walls. Embedded retaining walls – guidance for economic design Gaba, A R; Simpson, B; Powrie, W; Beadman, D R Construction Industry Research and Information Association CIRIA C580 © CIRIA 2003 RP629 ISBN 0 86017 580 4 British Library Cataloguing in Publication Data A catalogue record is available for this book from the British Library. Published by CIRIA, 6 Storey’s Gate, Westminster, London SW1P 3AU. All rights reserved. No part of this publication may be reproduced or transmitted in any form or by any means, including photocopying and recording, without the written permission of the copyright-holder, application for which should be addressed to the publisher. Such written permission must also be obtained before any part of this publication is stored in a retrieval system of any nature. This publication is designed to provide accurate and authoritative information in regard to the subject matter covered. It is sold and/or distributed with the understanding that neither the authors nor the publisher is thereby engaged in rendering a specific legal or any other professional service. While every effort has been made to ensure the accuracy and completeness of the publication, no warranty or fitness is provided or implied, and the authors and publisher shall have neither liability nor responsibility to any person or entity with respect to any loss or damage arising from its use. CIRIA C5802 Keywords Ground engineering, ground investigation and characterisation, piling, soil-structure interaction Reader interest Design, specification, construction, managers, clients and supervising engineers involved in civil and geotechnical works Classification AVAILABILITY Unrestricted CONTENT Subject area review STATUS Committee-guided USER Civil, geotechnical and structural engineers, engineering geologists 3. Acknowledgements Research contractor This book is the main output from CIRIA Research Project 629. It was prepared by Ove Arup and Partners Limited in conjunction with the University of Southampton and Bachy Soletanche Limited. Authors Asim Gaba is a director of Ove Arup & Partners Ltd. He was lead author of this book, and co-ordinated and managed inputs from the various contributors and advisers. He has extensive experience of embedded retaining wall design and construction, as well as of soil-structure interaction in relation to deep excavations and underground structures, particularly for deep basements and mass rapid transit projects in the UK, Hong Kong Singapore, Taiwan and Thailand. Brian Simpson is a director of Ove Arup & Partners Ltd, editor of Géotechnique (2000–2002) and a visiting professor at City University, London. He has long-term interests in the design of retaining walls, investigation of failures, numerical analysis and the development of Eurocode 7. He is a former Rankine lecturer and is the skills leader for geotechnics throughout the global Arup practice William Powrie is Professor of Geotechnical Engineering and head of the Department of Civil and Environmental Engineering at the University of Southampton. He works closely with industry on research encompassing retaining walls, groundwater control and landfill engineering. He is the author of a number of journal papers and a textbook on soil mechanics, and was awarded the ICE Telford Medal in 2001 for research on loads in temporary props used to support the deep excavation for the Jubilee Line Extension station at Canary Wharf. David Beadman collated the Bachy Soletanche Ltd contribution to the book, concentrating on the constructability and wall selection issues. He is an associate of Ove Arup & Partners Ltd, and is experienced in developing economic, buildable solutions for deep basement excavations, combining knowledge of retaining wall design, structural design and construction. Following CIRIA’s usual practice, the research project was guided by a steering group, which comprised: Steering group chair Mr J Findlay of Stent Foundations Steering group Dr D Bush Highways Agency Dr D Carder Transport Research Laboratory Mr S Everton Gibb Mr R Fernie Skanska Prof R Mair Cambridge University Mr B McGinnity London Underground Limited Mr D McNicholl Wardell Armstrong Mr A O’Brien Mott MacDonald Limited Prof D Potts Imperial College Mr D Rowbottom Corus Dr H St John Geotechnical Consulting Group Dr J Wilson WS Atkins Mr R Yenn TPS Consult CIRIA C580 3 4. Corresponding Dr N O’Riordan Rail Link Engineering member CIRIA manager CIRIA’s research manager for this project was Dr A J Pitchford. Project funders This project was funded by: Department of Trade and Industry (DTI) under the Partners in Innovation scheme Highways Agency Corus CIRIA’s Core Programme sponsors. Technical CIRIA and the authors gratefully acknowledge the support of these funding contributors organisations, the technical advice and help given by the members of the steering group and, in particular, the following individuals: Mr A Pickles Ove Arup and Partners Limited Mr J Smethurst Southampton University Professor J H Atkinson City University Dr D Borin Geosolve Limited Mr D Twine Rail Link Engineering Mr M J Puller Malcolm Puller Associates Mrs J Senior Ove Arup and Partners Limited Mr J Taylor Ove Arup and Partners Limited Note Recent UK Government reorganisation has meant that DETR responsibilities have been moved variously to the Department of Trade and Industry (DTI), the Office of the Deputy Prime Minister (ODPM), the Department for Environment, Food and Rural Affairs (DEFRA) and the Department for Transport (DfT). References made to government agencies in this publication should be read in this context. For clarification, readers should contact the Department of Trade and Industry. CIRIA C5804 5. Contents Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .2 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .3 List of figures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 List of tables . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .13 List of boxes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 Glossary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .16 Abbreviations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .18 1 INTRODUCTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19 1.1 Background to project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19 1.2 Objectives . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .20 1.3 Readership . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21 1.4 Applicability . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .21 1.5 Economic design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .22 1.6 Book layout . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 2 DESIGN CONSIDERATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27 2.1 Health and safety . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .28 2.2 Design concepts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .34 2.3 Design requirements and performance criteria . . . . . . . . . . . . . . . . . . . . .38 2.4 Limit states . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .39 2.5 Ground movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .42 2.6 Key points and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .65 3 CONSTRUCTION CONSIDERATIONS AND WALL SELECTION . . . .67 3.1 Construction methods for soil support . . . . . . . . . . . . . . . . . . . . . . . . . . .68 3.2 Types of embedded retaining walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .83 3.3 Wall selection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .87 3.4 Key points and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .90 4 ANALYSIS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91 4.1 Earth pressures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .91 4.2 Methods of analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .107 4.3 Effect of method of analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .127 4.4 Key points and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .130 5 DETERMINATION AND SELECTION OF PARAMETERS . . . . . . . . .133 5.1 Design parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .134 5.2 Investigation of ground and groundwater conditions . . . . . . . . . . . . . . .136 5.3 Assessment of drained/undrained soil conditions . . . . . . . . . . . . . . . . . .141 5.4 Determination of soil parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .142 5.5 Determination of groundwater pressures . . . . . . . . . . . . . . . . . . . . . . . . .161 5.6 Loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .166 5.7 Unplanned excavation of formation . . . . . . . . . . . . . . . . . . . . . . . . . . . .168 CIRIA C580 5 6. 5.8 Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .169 5.9 Selection of design parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .170 5.10 Key points and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .177 6 DESIGN OF WALL . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .183 6.1 Design philosophy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185 6.2 Design method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .185 6.3 ULS calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .188 6.4 SLS calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .194 6.5 Progressive failure check . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .197 6.6 Structural design of wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .197 6.7 Worked example . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205 6.8 Key points and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .205 7 DESIGN OF SUPPORT SYSTEMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .207 7.1 Propping systems . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .207 7.2 Berms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .213 7.3 Anchors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .220 7.4 Key points and recommendations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .221 8 AREAS OF FURTHER WORK AND RESEARCH . . . . . . . . . . . . . . . . .223 9 REFERENCES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .225 APPENDICES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .247 A1 EXAMPLE CDM RISK ASSESSMENT FORMS . . . . . . . . . . . . . . .249 A2 GROUND MOVEMENTS AND CASE HISTORY DATA . . . . . . . .253 A2.1 Ground movements due to wall installation . . . . . . . . . . . . . . . .253 A2.2 Ground heave . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .260 A2.3 Ground movements due to wall deflection . . . . . . . . . . . . . . . . .261 A2.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282 A3 WALL TYPES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .285 A3.1 Sheet piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .285 A3.2 Combi wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .288 A3.3 King post wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .288 A3.4 Contiguous pile . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .288 A3.5 Hard/soft secant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .290 A3.6 Hard/firm secant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .291 A3.7 Hard/hard secant . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .292 A3.8 Diaphragm walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .293 A3.9 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .295 A4 SOIL MECHANICS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .297 A4.1 Stress analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .297 A4.2 Drained and undrained conditions . . . . . . . . . . . . . . . . . . . . . . . .300 A4.3 Stress history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .302 A4.4 Soil shear strength . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .303 A4.5 Soil stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .310 A4.6 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .311 CIRIA C5806 7. A5 EFFECTS OF WALL INSTALLATION . . . . . . . . . . . . . . . . . . . . . . .313 A5.1 Concrete diaphragm and bored pile walls . . . . . . . . . . . . . . . . . .313 A5.2 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .315 A6 EARTH PRESSURE COEFFICIENTS . . . . . . . . . . . . . . . . . . . . . . .317 A6.1 Numerical procedure for calculating earth pressure coefficients . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .317 A6.2 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .326 A7 COMPARISON OF LUMPED MOMENT FACTORS WITH FACTOR ON STRENGTH METHOD IN LIMIT EQUILIBRIUM CALCULATIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .327 A7.1 Traditional design methods for embedded walls . . . . . . . . . . . . .327 A7.2 Factors . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .328 A7.3 Comparison of methods . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .329 A7.4 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .334 A8 REVIEW OF DESIGN METHODS TO BS 8002 (1994), EC7 (1995) AND BD42 (DMRB 2.1.2) (2000) . . . . . . . . . . . . . . . . . . . . . . . . . . . . .335 A8.1 UK codes of practice and design standards . . . . . . . . . . . . . . . . .335 A8.2 BS 8002 (1994) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .335 A8.3 Eurocode EC7 (1995) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .339 A8.4 BD 42/00 (DMRB 2.1.2) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .344 A8.5 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .352 A9 ANALYSIS OF BERMS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .355 A9.1 Multiple Coulomb wedge limit equilibrium analysis . . . . . . . . .355 A9.2 General finite element analysis of an earth berm removed in sections from in front of a long retaining wall . . . . . . . . . . . . . .357 A9.3 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .358 A10 EFFECT OF METHOD OF ANALYSIS . . . . . . . . . . . . . . . . . . . . . . .359 A10.1 Methods of analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .359 A10.2 Software packages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .359 A10.3 Problems analysed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .359 A10.4 Assumptions and analysis procedure . . . . . . . . . . . . . . . . . . . . . .362 A10.5 Results . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .364 A10.6 Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .378 A11 WORKED EXAMPLE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .379 CIRIA C580 7 8. List of figures Figure 1.1 Wall types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .19 Figure 1.2 Principal design stages and book layout . . . . . . . . . . . . . . . . . . . . . .23 Figure 1.3 Key issues considered in the book . . . . . . . . . . . . . . . . . . . . . . . . . .24 Figure 2.1 Decision paths for selection of appropriate wall type and construction sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .27 Figure 2.2 Conditions of contract in use in UK construction . . . . . . . . . . . . . . .29 Figure 2.3 CDM risk assessment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .33 Figure 2.4 Geotechnical categorisation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .35 Figure 2.5 Elements of geotechnical design . . . . . . . . . . . . . . . . . . . . . . . . . . . .36 Figure 2.6 Ultimate limit state examples . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .40 Figure 2.7 Movements due to water flow . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .46 Figure 2.8 Ground surface movements due to bored pile wall installation in stiff clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .48 Figure 2.9 Ground surface movements due to diaphragm wall installation in stiff clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .49 Figure 2.10 Typical ground movement pattern associated with excavation stress relief . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .51 Figure 2.11 Ground surface movements due to excavation in front of wall in stiff clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .55 Figure 2.12 Ground surface settlement due to excavation in front of wall in sand 56 Figure 2.13 Maximum lateral wall movement versus system stiffness . . . . . . . .56 Figure 2.14 Procedure for prediction of wall deflections and ground surface movements . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .57 Figure 2.15 Simple field of plastic deformation . . . . . . . . . . . . . . . . . . . . . . . . . .59 Figure 2.16 Relation between analysed lateral (propped) wall deflections and predicted ground surface settlements in stiff soil . . . . . . . . . . . . . . .60 Figure 2.17 Procedure for building damage assessment . . . . . . . . . . . . . . . . . . .62 Figure 2.18 Relationship between damage category, deflection ratio and horizontal tensile strain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .64 Figure 3.1 Decision paths for selection of appropriate wall type and construction sequence . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .67 Figure 3.2 Temporary and permanent works: Bristol underground car park. An example of the use of a sheet pile wall as the permanent wall, exposed and painted . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .69 Figure 3.3 Cantilever wall construction sequence . . . . . . . . . . . . . . . . . . . . . . .70 Figure 3.4 Top-down construction sequence . . . . . . . . . . . . . . . . . . . . . . . . . . .71 Figure 3.5 Top-down construction sequence at underground car park, Bristol .71 Figure 3.6 Bottom-up construction sequence . . . . . . . . . . . . . . . . . . . . . . . . . . .73 Figure 3.7 Bottom-up construction sequence, Copenhagen Metro . . . . . . . . . .74 Figure 3.8 Circular shaft under construction at Blackpool, Lancashire . . . . . . .75 Figure 3.9 Various support systems to sheet pile walls at Thelwall Viaduct, Merseyside . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .75 Figure 3.10 Temporary props spanning full width of excavation for the Mayfair car park, London . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .76 CIRIA C5808 9. Figure 3.11 The use of a berm and raking props . . . . . . . . . . . . . . . . . . . . . . . . .77 Figure 3.12 Berm with raking props at Canary Wharf, London . . . . . . . . . . . . .77 Figure 3.13 The use of a berm and a prop to the permanent structure . . . . . . . .77 Figure 3.14 Berm with low-level permanent propping at Batheaston Bypass . . .78 Figure 3.15 Anchored contiguous bored pile wall . . . . . . . . . . . . . . . . . . . . . . . .78 Figure 3.16 Typical connection detail at sheet pile wall/concrete slab . . . . . . . .80 Figure 3.17 Sheet pile wall/concrete slab connection at Bristol underground car park . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .81 Figure 3.18 Typical detail for couplers cast within a diaphragm wall panel . . . .81 Figure 3.19 Typical details of bent-out bars in diaphragm wall panel . . . . . . . . .81 Figure 3.20 Hinged slab: A406 North Circular Road, London . . . . . . . . . . . . . .82 Figure 3.21 Hinged joint: A406 North Circular Road, London . . . . . . . . . . . . . .82 Figure 4.1 Schematic stress history of an overconsolidated clay deposit (σ′v against σ′h) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .92 Figure 4.2 Rankine plastic equilibrium for a frictionless wall/soil interface translating horizontally . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .94 Figure 4.3 Coulomb’s method to calculate limiting active force for a frictionless wall/soil interface translating horizontally . . . . . . . . . . .95 Figure 4.4 Effect of wall friction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .96 Figure 4.5 Tension cracks: minimum total horizontal stress . . . . . . . . . . . . . .101 Figure 4.6 Additional lateral effective stress acting on the back of a wall due to a strip load running parallel to it . . . . . . . . . . . . . . . . . . . . .102 Figure 4.7 Pressure diagram for a line load . . . . . . . . . . . . . . . . . . . . . . . . . . .103 Figure 4.8 Concentrated and line load surcharges . . . . . . . . . . . . . . . . . . . . . .104 Figure 4.9 Enhancement factor on passive earth pressure coefficient for rough walls in close proximity . . . . . . . . . . . . . . . . . . . . . . . . . . . .105 Figure 4.10 Idealised stress distribution for an unpropped embedded cantilever wall at failure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .110 Figure 4.11 Approximate stress analysis for unpropped walls . . . . . . . . . . . . . .112 Figure 4.12 Normalised depths of embedment at failure . . . . . . . . . . . . . . . . . .113 Figure 4.13 Idealised stress distribution at failure for a stiff wall propped rigidly at the top . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .114 Figure 4.14 “Fixed earth support” effective stress distributions and deformations for an embedded wall propped at the top . . . . . . . . . . . . . . . . . . . .115 Figure 4.15 Stress analysis for an embedded wall propped at formation level .116 Figure 4.16 Forces acting on a stabilising base retaining wall . . . . . . . . . . . . . .117 Figure 4.17 King post wall design . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .118 Figure 4.18 Reduction of lateral stress in the retained soil due to arching on to a rigid prop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .120 Figure 4.19 Components of wall displacements and definition of a stiff wall . .121 Figure 4.20 Stress distributions behind and in front of stiff and flexible embedded walls . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .122 Figure 4.21 Comparison of types of analyses: effective stress . . . . . . . . . . . . .128 Figure 4.22 Comparison of types of analyses: total stress . . . . . . . . . . . . . . . . .129 Figure 5.1 Determination and selection of parameters for use in design calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .133 Figure 5.2 Decision-making process in site investigation . . . . . . . . . . . . . . . .139 CIRIA C580 9 10. Figure 5.3 Permeability and drainage characteristics of soils . . . . . . . . . . . . .145 Figure 5.4 Correlation between the in-situ coefficient of earth pressure and overconsolidation ratio for clays of various plasticity indices . . . .148 Figure 5.5 Influence of stress history on Ko and σh′ in a heavily overconsoldiated clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .149 Figure 5.6 Influence of the ratio of sample size to the fissure spacing on the strength measured in laboratory tests . . . . . . . . . . . . . . . . . . . . . . .152 Figure 5.7 Correlation between undrained shear strength and liquidity index 153 Figure 5.8 Correlation between N60 value and undrained shear strength and plasticity index for insensitive clays . . . . . . . . . . . . . . . . . . . . . . . .154 Figure 5.9 Strength envelope for a given pre-consolidation . . . . . . . . . . . . . .155 Figure 5.10 Effect of overconsolidation on the relationship between (N1)60 and peak angle of friction φ′peak . . . . . . . . . . . . . . . . . . . . . . . . . . .157 Figure 5.11 Derivation of N′ from SPT blowcount N60 . . . . . . . . . . . . . . . . . . .158 Figure 5.12 Stiffness-strain behaviour of soil with typical strain ranges for laboratory tests and structures . . . . . . . . . . . . . . . . . . . . . . . . . . . . .159 Figure 5.13 Various steady-state seepage flownets . . . . . . . . . . . . . . . . . . . . . .163 Figure 5.14 Linear steady-state seepage in uniform ground and the effect of excavation width . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .164 Figure 5.15 Design parameters – definition of terms . . . . . . . . . . . . . . . . . . . . .170 Figure 5.16 Temporary works design assumptions . . . . . . . . . . . . . . . . . . . . . .174 Figure 6.1 Design method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .184 Figure 6.2 Postulated failure mechanisms used to check toe stability . . . . . . .193 Figure 6.3 Determination of wall bending moments in SLS conditions from limit equilibrium calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . .196 Figure 6.4 Design of sheet pile walls to EC3, Part 5 . . . . . . . . . . . . . . . . . . . .200 Figure 6.5 Pile cross-section showing crack width calculation principles to BS 8110 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .204 Figure 6.6 Pile cross-section showing crack width calculation principles to EC2 as applied on the Copenhagen Metro project . . . . . . . . . . . . .204 Figure 7.1 Propped steel sheet piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .207 Figure 7.2 Definition of berm geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .214 Figure 7.3 Representation of a berm as an equivalent surcharge . . . . . . . . . . .215 Figure 7.4 Representation of a berm by means of a raised effective formation level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .215 Figure 7.5 Normalised wall top displacement at the centre of the unsupported section against degree of discontinuity β for different excavated bay lengths B . . . . . . . . . . . . . . . . . . . . . . . . . .217 Figure 7.6 Three-dimensional finite element mesh, wall and excavation geometry and assumed soil parameters . . . . . . . . . . . . . . . . . . . . . .218 Figure 7.7 Relationship between berm height and effective uniform ground level . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .219 Figure 7.8 Passive anchor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .220 Figure 7.9 Sketch of a typical ground anchorage . . . . . . . . . . . . . . . . . . . . . . .220 Figure A1.1 Risk assessment – decision justification form . . . . . . . . . . . . . . . .250 Figure A1.2 Risk assessment – record of selection . . . . . . . . . . . . . . . . . . . . . . .251 Figure A1.3 Risk register . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .252 CIRIA C58010 11. Figure A2.1 Observed maximum lateral wall deflections for excavations in London Clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .263 Figure A2.2 Normalised maximum wall deflection versus system stiffness . . .264 Figure A2.3 Ground surface settlement contours at New Palace Yard, London .281 Figure A2.4 Plan of the Hai-Hua building . . . . . . . . . . . . . . . . . . . . . . . . . . . . .282 Figure A3.1 Frodingham sheet pile sections and properties . . . . . . . . . . . . . . . .285 Figure A3.2 Larssen sheet pile sections and properties . . . . . . . . . . . . . . . . . . .286 Figure A3.3 Sheet pile wall installation, Portsmouth Harbour . . . . . . . . . . . . . .287 Figure A3.4 High-modulus sheet piles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .288 Figure A3.5 Contiguous pile wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .289 Figure A3.6 Contiguous bored pile wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .289 Figure A3.7 Hard/soft secant pile wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .290 Figure A3.8 Hard/soft secant pile wall as temporary works at North Greenwich station, London . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .291 Figure A3.9 Hard/firm secant pile wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .291 Figure A3.10 Hard/hard secant pile wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .292 Figure A3.11 Hard/hard secant pile wall and an example of top-down construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .293 Figure A3.12 Diaphragm wall panel and joint . . . . . . . . . . . . . . . . . . . . . . . . . . .293 Figure A3.13 Diaphragm wall construction at Canary Wharf station, London . .294 Figure A4.1 Normal and shear stresses acting on an imaginary plane within the cross-section plane . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .299 Figure A4.2 Mohr circles of stress . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .299 Figure A4.3 Schematic stress history of an overconsolidated clay . . . . . . . . . . .302 Figure A4.4 Typical stress-strain data for a loose (lightly overconsolidated or normally consolidated) soil and for dense (heavily overconsolidated) soil . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .304 Figure A4.5 Critical state line . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .305 Figure A4.6 Undrained state paths for clay samples having the same specific volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .305 Figure A4.7 Ring shear test data for undisturbed London Clay . . . . . . . . . . . . .306 Figure A4.8 Normalised peak and critical state . . . . . . . . . . . . . . . . . . . . . . . . .307 Figure A4.9 Mohr circles representation of undrained shear strength failure criterion in terms of total stresses for shearing at a constant specific volume . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .308 Figure A4.10 Failure after dissipation of negative excess pore water pressures induced on excavation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .309 Figure A4.11 Soil stiffness definition . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .310 Figure A5.1 Earth pressure coefficient profiles 1 m behind the centre of the primary panel during construction of the wall: three-dimensional analysis with 5 m panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .314 Figure A5.2 Earth pressure coefficient profiles normal to the centre of the primary panel following completion of the wall: three-dimensional analysis with 5 m panels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .314 Figure A6.1 Active and passive earth pressure coefficients, (β / φ′) = -1 . . . . .318 Figure A6.2 Active and passive earth pressure coefficients, (β / φ′) = -0.75 . . .319 Figure A6.3 Active and passive earth pressure coefficients, (β / φ′) = -0.5 . . . .320 Figure A6.4 Active and passive earth pressure coefficients, (β / φ′) = -0.25 . . .321 CIRIA C580 11 12. Figure A6.5 Active and passive earth pressure coefficients, (β / φ′) = 0 . . . . . .322 Figure A6.6 Active and passive earth pressure coefficients, (β / φ′) = 0.25 . . . .323 Figure A6.7 Active and passive earth pressure coefficients, (β / φ′) = 0.5 . . . . .324 Figure A6.8 Active and passive earth pressure coefficients, (β / φ′) = 0.75 . . . .325 Figure A6.9 Active and passive earth pressure coefficients, (β / φ′) = 1 . . . . . .326 Figure A7.1 Methods of assessing the ratio of restoring moments to overturning moments . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .327 Figure A7.2 Wall geometry for general analysis case and range of variables . .329 Figure A7.3 Equivalent Fr, values for Fs = 1.2 . . . . . . . . . . . . . . . . . . . . . . . . . .331 Figure A7.4 Equivalent Fnp, values for Fs = 1.2 . . . . . . . . . . . . . . . . . . . . . . . . .332 Figure A7.5 Equivalent Fp, values for Fs = 1.2 . . . . . . . . . . . . . . . . . . . . . . . . . .333 Figure A9.1 Modified equilibrium analysis approach: multiple Coulomb wedge analysis (undrained) in terms of total stresses for a retaining wall supported by an earth berm . . . . . . . . . . . . . . . . . . .356 Figure A10.1 Example 1 – cantilever wall: effective stress analysis . . . . . . . . . .360 Figure A10.2 Example 2 – propped wall: effective stress analysis . . . . . . . . . . . .360 Figure A10.3 Example 3 – cantilever wall: total stress analysis . . . . . . . . . . . . . .361 Figure A10.4 Example 4 – propped wall: total stress analysis . . . . . . . . . . . . . . .361 Figure A10.5 Results for Example 1 – cantilever wall: effective stress analysis, ULS calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .365 Figure A10.6 Results for Example 1 – cantilever wall: effective stress analysis, SLS calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .366 Figure A10.7 Results for Example 2 – propped wall: effective stress analysis, ULS calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .367 Figure A10.8 Results for Example 2 – propped wall: effective stress analysis, SLS calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .368 Figure A10.9 Results for Example 3 – cantilever wall: total stress analysis, ULS calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .369 Figure A10.10 Results for Example 3 – cantilever wall: total stress analysis, SLS calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .370 Figure A10.11 Results for Example 4 – propped wall: total stress analysis, ULS calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .371 Figure A10.12 Results for Example 4 – propped wall: total stress analysis, SLS calculations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .372 Figure A10.13 Example 2 – singly propped wall: effective stress, ULS calculations. Effects of groundwater pressures . . . . . . . . . . . . . . . .375 Figure A10.14 Example 2 – singly propped wall: effective stress, SLS calculations. Effects of groundwater pressures . . . . . . . . . . . . . . . .376 Figure A11.1 Worked example geometry . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .379 Figure A11.2 Top-down construction sequence . . . . . . . . . . . . . . . . . . . . . . . . . .381 Figure A11.3 Limiting wall friction and adhesion: wall supporting large vertical loads . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .384 Figure A11.4 Calculated ULS and SLS wall bending moment envelopes . . . . . .385 Figure A11.5 Estimated ground surface settlement from computed SLS FREW wall deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .387 Figure A11.6 Estimated ground surface settlement due to wall installation and deflection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .388 CIRIA C58012 13. List of tables Table 2.1 Key performance considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .38 Table 2.2 Ground surface movements due to bored pile and diaphragm wall installation in stiff clay . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .50 Table 2.3 Support stiffness categories . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .54 Table 2.4 Ground surface movements due to excavation in front of bored pile, diaphragm wall and sheet pile walls wholly embedded in stiff clays . . .54 Table 2.5 Classification of visible damage to walls . . . . . . . . . . . . . . . . . . . . . . . .63 Table 3.1 Cantilever wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .70 Table 3.2 Top-down construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .72 Table 3.3 Tolerances for top-down piles and plunged columns . . . . . . . . . . . . . . .73 Table 3.4 Bottom-up construction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .74 Table 3.5 Ground anchorages . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .79 Table 3.6 Wall/slab connection types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .80 Table 3.7 Wall types . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .84 Table 3.8 Typical applications of embedded retaining walls . . . . . . . . . . . . . . . . .85 Table 3.9 Relative costs to assist choice of wall . . . . . . . . . . . . . . . . . . . . . . . . . . .86 Table 3.10 Measures for dealing with obstructions . . . . . . . . . . . . . . . . . . . . . . . . .88 Table 3.11 Environmental issues throughout the life-cycle of the wall . . . . . . . . . .89 Table 4.1 Advantages and limitations of common methods of retaining wall analysis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .109 Table 4.2 Values of Young’s modulus E and second moment of cross-sectional area I for various embedded retaining wall types . . . . . . . . . . . . . . . . .125 Table 5.1 Soil parameters required for various calculation/analysis methods . . .135 Table 5.2 Typical ground investigation techniques used in stiff overconsolidated soils to establish stratigraphy . . . . . . . . . . . . . . . . . .140 Table 5.3 Effect of fabric on soil properties . . . . . . . . . . . . . . . . . . . . . . . . . . . . .141 Table 5.4 Publications giving typical properties for stiff clays commonly encountered in the UK . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .144 Table 5.5 Index properties to be determined . . . . . . . . . . . . . . . . . . . . . . . . . . . . .144 Table 5.6 Typical unit weight of soils and fills . . . . . . . . . . . . . . . . . . . . . . . . . . .145 Table 5.7 Comparison of common methods of permeability determination . . . .147 Table 5.8 Undrained shear strength of clays . . . . . . . . . . . . . . . . . . . . . . . . . . . . .154 Table 5.9 φ′crit for clay soils . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .156 Table 5.10 Values of A, B and C for siliceous sands and gravels . . . . . . . . . . . . . .158 Table 5.11 Highway live loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167 Table 5.12 Railway live loading . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .167 Table 6.1 Fs factors appropriate for use in design calculations . . . . . . . . . . . . . . .185 Table 6.2 Corrosion rates for steel piling in natural environments . . . . . . . . . . . .198 Table 6.3 Allowable bending stresses for steel sheet piling . . . . . . . . . . . . . . . . .199 Table A2.1 Wall installation effects – case history data: Clough and O’Rourke (1990) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .255 Table A2.2 Wall installation effects – case history data: Thompson (1991) . . . . . .256 CIRIA C580 13 14. Table A2.3 Wall installation effects – case history data: Carder (1995) . . . . . . . . .258 Table A2.4 Wall installation effects – case history data: Carder et al (1997) . . . . .259 Table A2.5 Ground heave case studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .262 Table A2.6 Average δhmax values due to excavation in front of walls embedded in stiff soil for data where δhmax < 0.3 per cent H . . . . . . . . . . . . . . . . .265 Table A2.7 Wall deflection effects – case history data: Clough and O’Rourke (1990) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .266 Table A2.8 Wall deflection effects – case history data: Carder (1995) . . . . . . . . . .268 Table A2.9 Wall deflection effects – case history data: Fernie and Suckling (1996) 270 Table A2.10 Wall deflection effects – case history data: Carder et al (1997) . . . . . .272 Table A2.11 Wall deflection effects – case history data: Long (2001) . . . . . . . . . . .273 Table A3.1 Contiguous pile wall – typical diameters and spacing . . . . . . . . . . . . .289 Table A3.2 Hard/soft secant pile wall – typical diameters and spacing . . . . . . . . .290 Table A3.3 Hard/firm secant pile wall – typical diameters and spacing . . . . . . . . .292 Table A3.4 Hard/hard secant pile wall – typical diameters and spacing . . . . . . . . .292 Table A3.5 Diaphragm wall – typical panel widths . . . . . . . . . . . . . . . . . . . . . . . . .294 Table A7.1 Commonly adopted ULS factor values . . . . . . . . . . . . . . . . . . . . . . . . .328 Table A7.2 Summary of equivalent factors of safety . . . . . . . . . . . . . . . . . . . . . . .330 Table A8.1 Partial factors (γf and γm) – ultimate limit states in persistent and transient situations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .341 Table A8.2 BD 42/00 (DMRB 2.1.2) recommended methods for determining a stable wall geometry in stiff clays . . . . . . . . . . . . . . . . . . . . . . . . . . . . .346 Table A8.3 Partial factors γfl . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .349 Table A8.4 Comparison of retaining wall design assumptioms and factors . . . . . .351 Table A10.1 Principal assumptions made in calculations . . . . . . . . . . . . . . . . . . . . .363 Table A11.1 Summary of ground parameters . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .380 Table A11.2 Soil design parameters – ULS calculations . . . . . . . . . . . . . . . . . . . . . .382 Table A11.3 Soil design parameters – SLS calculations . . . . . . . . . . . . . . . . . . . . . .386 Table A11.4 ULS values of maximum wall bending moment and shear force . . . . .389 Table A11.5 SLS prop forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .390 Table A11.6 ULS prop forces . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .390 CIRIA C58014 15. List of boxes Box 2.1 Typical roles in embedded retaining wall design . . . . . . . . . . . . . . . . . . . .30 Box 2.2 Stress paths for soil elements near an excavation retained by a cast- in-situ embedded wall . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .44 Box 2.3 Typical movement profiles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .52 Box 2.4 System stiffness . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .58 Box 2.5 Procedure for stage 2 damage category assessment . . . . . . . . . . . . . . . . . .64 Box 4.1 Theoretical depths of tension cracks by the Rankine and Coulomb analyses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .100 Box 4.2 Steps involved in a typical limit equilibrium analysis . . . . . . . . . . . . . . . .111 Box 4.3 Changing wall EI to allow for cracking, creep and relaxation of concrete . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .125 Box 5.1 Effect of groundwater pressure on retaining wall design . . . . . . . . . . . . .165 Box 5.2 Moderately conservative profile of undrained shear strength . . . . . . . . . .172 Box 6.1 The design method: sequential steps . . . . . . . . . . . . . . . . . . . . . . . . . . . . .186 Box 7.1 The distributed prop load design method . . . . . . . . . . . . . . . . . . . . . . . . .211 Box 7.2 Construction sequence analysed by Easton et al . . . . . . . . . . . . . . . . . . . .219 CIRIA C580 15 16. Glossary analysis The process of breaking down a design into its constituent parts and of calculating the behaviour of each part. client An organisation or individual using the services of construction professionals in order to invest in new building or construction work. conceptual design The identification of an appropriate design solution by qualitatively assessing the strengths and weaknesses of a range of possible design variants, without recourse to detailed analyses. desk study An examination of all existing information concerning a site (eg geological maps, previous borehole records, aerial photographs) to determine ground conditions and previous land use. engineering judgement A feel for the appropriateness of a situation, from the narrowest technical details to the broadest concepts of planning. geotechnical adviser A chartered engineer or a chartered geologist with five years of practice as a geotechnical specialist (Site Investigation Steering Group, 1993). geotechnical engineer A chartered engineer with at least one year of post- graduate experience in geotechnics and a post-graduate qualification in geotechnical engineering or engineering geology, equivalent at least to an MSc, or a chartered engineer with at least three years of post-graduate experience in geotechnics (Site Investigation Steering Group, 1993). geotechnical risk The risk posed to construction by the ground or groundwater conditions at a site. ground investigation The sub-surface field investigation, with the associated sampling, testing and factual reporting. See site investigation. ground model A conceptual model based on the geology and morphology of the site, and used to speculate on likely ground and groundwater conditions and their variability. hazard An event, process or mechanism that could affect the performance of an embedded retaining wall and prevent performance objectives from being met. likelihood The probability that an event will occur. CIRIA C58016 17. mitigation The limitation of the undesirable effects of a particular event. moderately conservative A cautious estimate of soil parameters, loads and geometry – worse than the probabilisitic mean but not as severe as a worst credible parameter value. Sometimes termed a conservative best estimate. project manager The individual or organisation responsible for managing a project. risk The combination of the probability and consequences of a hazard occurring. risk assessment A structured process of identifying hazards, their probability and consequence of occurring, and their likely impact on the performance of the retaining wall. risk mitigation Measures taken to either remove a hazard or to minimise the likelihood or consequences of it occurring to an acceptable level, including monitoring, and remedial action. risk register A list of risks arising from relevant hazards and the benefits of mitigating them. rupture surface The detachment surface on which differential movement occurs. serviceability limit state State of deformation of a retaining wall such that its use is affected, its durability is impaired or its maintenance requirements are substantially increased. Alternatively, such movement that may affect any supported or adjacent infrastructure, eg track, road or canal. See ultimate limit state. site investigation The assessment of the site, including desk study, planning and directing the ground investigation, and interpretation of the factual report. ultimate limit state State of collapse, instability or forms of failure that may endanger property or people or cause major economic loss. See serviceability limit state. worst credible The worst value of soil parameters, loads and geometry that the designer realistically believes might occur. For further definitions and information, the reader is referred to technical dictionaries including the Penguin dictionary of civil engineering (Scott, 1991) and the Dictionary of geotechnical engineering (Somerville and Paul, 1983). CIRIA C580 17 18. Abbreviations CDM Construction (Design and Management) Regulations 1994 DETR Department of the Environment, Transport and Regions DMRB Design Manual for Roads and Bridges FPS Federation of Piling Specialists HA Highways Agency ICE Institution of Civil Engineers LUL London Underground Limited DPL distributed prop load SISG Site Investigation Steering Group SLS serviceability limit state SPT Standard Penetration Test ULS ultimate limit state U100 102 mm-diameter driven tube sample CIRIA C58018 19. 1 Introduction An earth retaining wall is required to withstand forces exerted by a vertical or near- vertical ground surface. An embedded retaining wall is one that penetrates the ground at its base and obtains some lateral support from it. The wall may also be supported by structural members such as props, berms, ground anchors and slabs. It may be freestanding or it may provide support to a superstructure. This book provides guidance on the selection and design of vertical embedded retaining walls. It covers all types of embedded walls; see Figure 1.1. Figure 1.1 Wall types It is possible to make economies in embedded retaining walls by selecting an appropriate wall type and support system for the envisaged construction sequence and long-term use. It is important to adopt a clear, unambiguous design method and to follow best practice in ground investigation, laboratory and field-testing, design analysis and the use of good-quality case history data. This book provides guidance on all these points. 1.1 BACKGROUND TO PROJECT CIRIA Report 104 (Padfield and Mair, 1984) Design of retaining walls embedded in stiff clay has been hugely influential. Although strictly applicable to the design of single-propped or cantilever walls embedded in stiff overconsolidated clay, the principles presented in the book have been applied to a wide range of wall types and soils in the UK and overseas, including multi-propped embedded walls and even non- embedded walls. It has also formed the model for other documents providing design guidance such as the recently published BD 42/00 Design of embedded retaining walls and bridge abutments (Design Manual for Roads and Bridges, DMRB 2.1.2). CIRIA C580 19 20. Since CIRIA Report 104 was published, several retaining wall design guidance documents and codes of practice relevant to embedded walls have been issued, most notably: BS 8002 (1994) Code of practice for earth retaining structures. The latest amendment to this code was issued in September 2001 DD ENV 1997-1 Eurocode 7 (1995) Geotechnical design. Part 1 General rules. This document is being revised BD 42/00 (Design Manual for Roads and Bridges, DMRB 2.1.2) Design of embedded retaining walls and bridge abutments British Steel (1997) Piling handbook 7th edition Hong Kong Government (1994) Geoguide 1, Guide to retaining wall design Nicholson et al (1999) The Observational Method in ground engineering – principles and applications (CIRIA R185) Twine and Roscoe (1999) Temporary propping of deep excavations – guidance on design (CIRIA C517) Williams and Waite (1993) The design and construction of sheet piled cofferdams (CIRIA SP95). In addition to the above, many technical papers and textbooks have been published. The above documents do not provide consistent and harmonious design advice, and many omit detailed treatment of modern numerical analysis methods. The multiplicity of documents, and the varied guidance they offer, results in confusion (which is costly to designers) and poor economy in construction (which is costly to constructors and clients). There is therefore a need for a coherent and authoritative publication that collates the best ideas and experiences available in British practice and provides a clear path through the many alternative design approaches. That is the aim of this book. CIRIA commissioned the research in November 2000. Ove Arup & Partners Ltd undertook the project with assistance from the University of Southampton and Bachy Soletanche Limited. The steering group that guided the work represented clients, consultants, contractors and academic institutions. The authors consulted widely via a questionnaire, consultation workshop and literature searches. 1.2 OBJECTIVES This book provides guidance on the design of embedded retaining walls. Following the guidance should enable users to achieve economy in the resulting retaining structure and its support system while maintaining simplicity, so far as possible, but also facilitating more complex approaches where they give an advantage. The book: offers best practice guidance for the design of embedded retaining walls consistent with recent research and current analytical techniques describes and compares existing design methods for such walls discusses available wall types and construction methods provides construction costs data to guide the reader in selecting wall types appropriate to particular requirements. This publication supersedes CIRIA Report 104 (Padfield and Mair, 1984). CIRIA C58020 21. 1.3 READERSHIP CIRIA C580 is intended for use by those concerned with the selection, design and construction of embedded retaining walls. In addition to providing guidance to designers, the book also: gives background information on wall selection, construction methods and associated ground movements for clients and owners and their technical advisers presents geotechnical principles and guidance to structural and geotechnical engineers and to students who wish to gain an appreciation of the issues relevant to the selection, design and construction of an embedded retaining wall acts as a reference for more experienced geotechnical engineers. 1.4 APPLICABILITY CIRIA C580 covers the design of temporary and permanent cantilever, anchored, single- and multi-propped retaining walls supported by embedment in stiff clay and other competent soils. The book’s principles are applicable to a wide range of fine- grained and coarse-grained soils in the UK and overseas. The design of walls embedded in soft clay and those socketed into rock is beyond the scope of this publication. Typical British soils to which this book is applicable include London Clay, Oxford Clay, Gault Clay, Lias Clay, Atherfield Clay, Weald Clay, Barton Clay, Kimmeridge Clay, Lambeth Beds, Mercia Mudstone, and glacial tills. These soils have experienced high overburden pressures in their geological history, which have caused them to consolidate to a dense state. Subsequent erosion of the upper soil horizons, or the removal of Quaternary ice cover, has resulted in significant unloading and swelling. These soils typically exhibit in situ moisture contents that are lower than they would have been if no overconsolidation had occurred. This geological history results in soils that: may be fissured have an in situ earth pressure coefficient, Ko, that is greater than unity have an undrained shear strength that is significantly greater than that of a normally consolidated soil at similar depth exhibit a peak shear strength at low strains and reduced shear strength at high strains. Few walls are constructed entirely in stiff overconsolidated fine-grained soils. Although the wall may be embedded in such soils, it is likely that it will also retain other soils, such as made ground, river gravels and other alluvial deposits. The principles presented in this book also apply to this common situation. The authors have adopted the geotechnical categorisation proposed by EC7 (1995). It applies to the design of embedded retaining walls for geotechnical categories 1 (small and relatively simple structures) and 2 (conventional types of structures with no abnormal risks or unusual or exceptionally difficult ground or loading conditions). It does not specifically address the design requirements of walls for geotechnical category 3 (very large or unusual structures, structures involving abnormal risks, or unusual or exceptionally difficult ground or loading conditions and structures in highly seismic areas), although the general principles presented in this book will also apply to these structures. Geotechnical categories are defined and discussed in Section 2.2.2. Ground engineering requires a thorough knowledge and understanding of basic principles and the application of sound engineering judgement based on experience. This book is not a substitute for professional knowledge. If in doubt, seek appropriate advice. CIRIA C580 21 See also 2.2.2 Geotechnical characterisation of retaining walls 22. 1.5 ECONOMIC DESIGN Economy can be achieved by: ensuring ease of construction and minimising construction duration optimising the use of materials applying appropriate design effort. The biggest economies will be available at the outset of a project during the selection of an appropriate method and sequence of construction, wall type and the optimisation of the temporary and permanent use of the retaining structure. Achieving economy requires commitment and adherence to an approach that necessitates a holistic view to be taken of project requirements. Whole-life costs should be considered. A robust design that minimises long-term maintenance requirements may be appropriate in some circumstances. A design that minimises wall dimensions and material use but increases construction duration because it is difficult to build may not result in overall economy. The designer alone cannot achieve the most cost-effective solution in isolation from the client and the constructor. The client, designer and constructor and, where appropriate, the architect and the quantity surveyor, should be involved as early as possible to: optimise the temporary and permanent use of the retaining structure (such as adopting one wall instead of two to serve both the temporary and permanent requirements) that is also compatible with long-term maintenance requirements establish appropriate design and performance criteria for the retaining structure, such as acceptable limits for wall deflection and associated ground movements, crack width criteria consider appropriate wall type consider appropriate method and sequence of construction to ensure buildability with minimum construction duration. Initial ideas should be reviewed and alternatives explored before agreeing the preferred solution. It is important to involve individuals with appropriate qualifications and experience at all stages of the project and to maintain adequate continuity and communication between the personnel involved in data collection, design and construction. The involvement of the constructor at an early stage should minimise wasteful abortive work arising from design changes. Where the design of a wall is governed by temporary works considerations, a risk- based approach to design may lead to significant savings. Using the Observational Method may result in the most cost effective design solution for temporary and permanent works (Section 5.9.1). However, in this circumstance, appropriate contractual arrangements should be in place to permit the necessary integrated interactive approach to be taken on site between design and construction. A clear, unambiguous design method that eliminates confusion will avoid unnecessary design effort. The choice of analysis method can result in significant savings in the wall structure. For example, propped or anchored walls designed using soil-structure interaction methods will be shorter, and computed wall bending moments will be smaller, than those designed using limit equilibrium methods (Section 4.3). Also, savings in material use of about 25–30 per cent are possible if plastic design is applied to sheet pile walls (Section 6.6.3). In the UK, it may not be possible to realise such savings, as it is often necessary to adopt sheet pile sections that are of greater thickness than those determined from the analysis of the section in service in order to CIRIA C58022 See also A10 Effect of method of analysis 2.1.3 Risk assessment and management 2.2.2 Geotechnical categorisation of retaining walls 3 Construction considerations and wall selection 4.3 Effect of method of analysis 5.9.1 Temporary works design 6 Design of wall 6.6.3 Steel sheet pile walls 23. withstand the driving forces. Procedures for higher wall categories can be used to justify more economic design. For example, the design of walls to geotechnical category 2 can be used to justify a more economic design for structures that would otherwise be classified as category 1. The higher investigation and design costs of a geotechnical category 2 wall should be balanced against the potential savings in materials and construction over a category 1 design. 1.6 BOOK LAYOUT Figure 1.2 shows the principal design stages and the corresponding sections of this book. For readers needing guidance on specific issues, Figure 1.3 provides a map of the sections discussing key issues. Figure 1.2 Principal design stages and book layout CIRIA C580 23 24. Figure 1.3 Key issues considered in the book CIRIA C58024 25. Cross-references guide users between related subjects in different sections. Details are presented in boxes, separately from the main text. Appendices provide background information, a commentary on current practices and a list of case history data. The book is organised into eight largely self-contained chapters. In view of the anticipated wide readership (Section 1.3), the beginning of each chapter outlines the target readership likely to gain most from the content of that chapter. Key points of guidance and recommendations are highlighted in bold within the main text and appear again at the end of the relevant chapter. Chapter 1 sets out the objectives of the book and its applicability. Chapters 2 and 3 help the reader select the appropriate wall type and construction sequence. Some of the issues covered in these chapters are interrelated. Chapter 2 provides guidance on the determination of the key wall design criteria, health and safety issues, risk assessment and management, site-specific constraints and project-specific requirements. Guidance is also provided on the estimation and effects of ground movements associated with wall installation and performance. Chapter 3 reviews wall types and available construction sequences. The advantages and limitations of different construction sequences and wall types are compared and guidance is provided on the selection of the most appropriate sequence and wall type to satisfy particular site and project requirements. This chapter also presents construction cost data relating to wall types and construction methods. Chapter 4 presents key principles of soil behaviour relevant to embedded retaining walls and the determination of earth pressures. Soil-structure interaction and methods for its analytical modelling are also discussed. Chapter 5 provides guidance on the determination and selection of parameters for use in design calculations. Advice on the assessment of drained or undrained ground behaviour is given together with guidance on the selection of parameters appropriate for temporary works and permanent works design. Chapter 6 offers best practice guidance on the geotechnical and structural design of the wall. Chapter 7 presents best practice guidance on the design of propping systems, berms and anchors for lateral support to the wall. Chapter 8 identifies areas of further work and research. CIRIA C580 25 26. CIRIA C58026