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ICE manual of geotechnical engineering Volume 2 Geotechnical Design, Construction and Verification Edited by John Burland Imperial College London, UK Tim Chapman Arup Geotechnics, UK Hilary Skinner Donaldson Associates Ltd, UK Michael Brown University of Dundee, UK ice | manuals ICE__MGE_Prelims_Vol 2.indd iii ICE__MGE_Prelims_Vol 2.indd iii 2/10/2012 7:06:30 PM 2/10/2012 7:06:30 PM Published by ICE Publishing, 40 Marsh Wall, London E14 9TP, UK www.icevirtuallibrary.com Full details of ICE Publishing sales representatives and distributors can be found at: www.icevirtuallibrary.com/info/printbooksales First published 2012 Future titles in the ICE Manuals series from ICE Publishing ICE manual of structural design ICE manual of project management Currently available in the ICE Manual series from ICE Publishing ICE manual of bridge engineering – second edition. 978-0-7277-3452-5 ICE manual of construction materials – two volume set. 978-0-7277-3597-3 ICE manual of health and safety in construction. 978-0-7277-4056-4 ICE manual of construction law. 978-0-7277-4087-8 ICE manual of highway design and management. 978-0-7277-4111-0 www.icemanuals.com A catalogue record for this book is available from the British Library ISBN: 978-0-7277-5707-4 (volume I) ISBN: 978-0-7277-5709-8 (volume II) ISBN: 978-0-7277-3652-9 (two volume set) © Institution of Civil Engineers 2012 ICE Publishing is a division of Thomas Telford Ltd, a wholly owned subsidiary of the Institution of Civil Engineers (ICE). All rights, including translation, reserved Except as permitted by the Copyright, Designs and Patents Act 1988, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior written permission of the Publisher, ICE Publishing, 40 Marsh Wall London E14 9TP, UK. This book is published on the understanding that the authors are solely responsible for the statements made and opinions expressed in it and that its publication does not necessarily imply that such statements and/or opinions are or refl ect the views or opinions of the publishers. While every effort has been made to ensure that the statements made and the opinions expressed in this publication provide a safe and accurate guide, no liability or responsibility can be accepted in this respect by the authors or publishers. The authors and the publisher have made every reasonable effort to locate, contact and acknowledge copyright owners. The publisher wishes to be informed by copyright owners who are not properly identifi ed and acknowledged in this publication so that we may make necessary corrections. Permission to reproduce extracts from British Standards is granted by the British Standard Institution (BSI), www.bsigroup.com. No other use of this material is permitted. British Standards can be obtained from the BSI online shop: http://shop.bsigroup.com. Typeset by Newgen Imaging Sytems Pvt. Ltd., Chennai, India Printed and bound in Great Britain by Bell & Bain Ltd, Glasgow ICE__MGE_Prelims_Vol 2.indd iv ICE__MGE_Prelims_Vol 2.indd iv 1/11/2012 2:29:28 PM 1/11/2012 2:29:28 PM ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com xiii Preface We began to formulate the initial ideas for this Manual as early as 2006. It had become apparent to us that civil and structural engineers not specialising in geotechnics face a daunting knowledge gap when they come up against a geotechnical problem. Most civil engineers leave university with very little grounding in geotechnical engineering. They will have a fair grasp of applied mechanics (mainly aimed at structural engineering). They will have had a basic introduction to geology and they will have studied the elements of soil mechanics and rock mechanics. But a recent graduate usually lacks a coherent understanding of the approach to, and methods of, geotechnical engineering and how these differ from other more widely prac- tised branches of engineering. A survey carried out by ICE Publishing showed that information tends to be obtained from a wide range of sources through word of mouth, the internet and various publications. For the young practitioner this leads to a fragmented approach. Much of the geotechnical material is written by specialists for specialists and its ad hoc application by a general practitioner is often inappropriate and can be extremely dangerous. We felt that it would be of great benefi t to our profession to provide a single fi rst- port-of-call authoritative reference source aimed at informing the less experienced engineer. To our delight this concept was endorsed by the ICE Best Practice Panel and the British Geotechnical Association and has offered a unique opportunity to provide authoritative guidance within a coherent framework of good geotech- nical engineering. This ICE Manual of Geotechnical Engineering has been a labour of love! The contribution of 99 contributors and 10 section editors has made it possible to distil a great deal of experience from the profession into the books you see here. Don’t imagine this will cover everything that a geotechnical engineer will face in their career – but it provides a “starting point” from which to build experience whilst remaining grounded in robust fundamentals. As mentioned previously, the Manual is aimed at people in the early stage of their careers who need a readily accessible source of information when working in new aspects of geotechnical engineering. However it is expected that it also should prove valuable to all geotechnical engineering professionals. The aim has been to produce a manual that addresses the practice of geotechnical engineering in the 21st century including contemporary procurement, process and design standards and procedures. The grouping of chapters has been carefully chosen to facilitate a multi-disciplinary and holistic approach to the solution of construction challenges. A key message is the importance of drawing on “well-winnowed experience” for the smooth and reliable execution of projects. Such experience is best gained by working closely with a suitably experienced design or construction team. It is hoped that this Manual will help in the training and development of the next generation of geotechnical engineers and will act as a useful source of reference to those with more experience. The Editors are grateful to all those contributors and section editors who have generously given so much of their time and knowledge in producing such a comprehensive book. John Burland, Tim Chapman, Hilary Skinner and Michael Brown ICE__MGE_Prelims_Vol 2.indd xiii ICE__MGE_Prelims_Vol 2.indd xiii 2/10/2012 7:06:31 PM 2/10/2012 7:06:31 PM ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com v Contents Volume II Foreword and endorsement xi Preface xiii List of contributors xv SECTION 5: Design of foundations 729 Section Editor: A. S. O’Brien Chapter 51: Introduction to Section 5 731 A. S. O’Brien Chapter 52: Foundation types and conceptual design principles 733 A. S. O’Brien 52.1 Introduction 733 52.2 Foundation types 734 52.3 Foundation selection – conceptual design principles 735 52.4 Allowable foundation movement 747 52.5 Design bearing pressures 752 52.6 Parameter selection – introductory comments 754 52.7 Foundation selection – a brief case history 759 52.8 Overall conclusions 763 52.9 References 763 Chapter 53: Shallow foundations 765 A. S. O’Brien and I. Farooq 53.1 Introduction 765 53.2 Causes of foundation movements 765 53.3 Construction processes and design considerations 768 53.4 Applied bearing pressures, foundation layout and interaction effects 773 53.5 Bearing capacity 774 53.6 Settlement 778 53.7 Information requirements and parameter selection 789 53.8 Case history for a prestigious building on glacial tills 796 53.9 Overall conclusions 799 53.10 References 800 Chapter 54: Single piles 803 A. Bell and C. Robinson 54.1 Introduction 803 54.2 Selection of pile type 803 54.3 Axial load capacity (ultimate limit state) 804 54.4 Factors of safety 814 54.5 Pile settlement 814 54.6 Pile behaviour under lateral load 816 54.7 Pile load testing strategy 818 54.8 Defi nition of pile failure 820 54.9 References 820 Chapter 55: Pile-group design 823 A. S. O’Brien 55.1 Introduction 823 55.2 Pile-group capacity 824 55.3 Pile-to-pile interaction: vertical loading 827 55.4 Pile-to-pile interaction: horizontal loading 834 55.5 Simplifi ed methods of analysis 834 55.6 Differential settlement 841 55.7 Time-dependent settlement 841 55.8 Optimising pile-group confi gurations 841 55.9 Information requirements for design and parameter selection 843 55.10 Ductility, redundancy and factors of safety 846 55.11 Pile-group design responsibility 847 55.12 Case history 847 55.13 Overall conclusions 850 55.14 References 850 Chapter 56: Rafts and piled rafts 853 A. S. O’Brien, J. B. Burland and T. Chapman 56.1 Introduction 853 56.2 Analysis of raft behaviour 854 56.3 Structural design of rafts 860 56.4 Design of a real raft 861 56.5 Piled rafts, conceptual design principles 863 56.6 Raft-enhanced pile groups 868 56.7 Pile-enhanced rafts 879 56.8 A case history of a pile-enhanced raft – the Queen Elizabeth II Conference Centre 883 56.9 Key points 884 56.10 References 885 Chapter 57: Global ground movements and their effects on piles 887 E. Ellis and A. S. O’Brien 57.1 Introduction 887 57.2 Negative skin friction 888 57.3 Heave-induced tension 891 57.4 Piles subject to lateral ground movements 893 57.5 Conclusions 897 57.6 References 897 Chapter 58: Building on fi lls 899 H. D. Skinner 58.1 Introduction 899 58.2 Engineering characteristics of fi ll deposits 899 58.3 Investigation of fi lls 900 58.4 Fill properties 902 58.5 Volume changes in fi lls 904 58.6 Design issues 907 58.7 Construction on engineered fi lls 909 58.8 Summary 910 58.9 References 910 ICE__MGE_Prelims_Vol 2.indd v ICE__MGE_Prelims_Vol 2.indd v 2/10/2012 7:06:30 PM 2/10/2012 7:06:30 PM vi www.icemanuals.com ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers Contents – volume II ice | manuals Chapter 59: Design principles for ground improvement 911 R. Essler 59.1 Introduction 911 59.2 General design principles for ground improvement 912 59.3 Design principles for void fi lling 913 59.4 Design principles for compaction grouting 914 59.5 Design principles for permeation grouting 916 59.6 Design principles for jet grouting 924 59.7 Design principles for vibrocompaction and vibroreplacement 929 59.8 Design principles for dynamic compaction 933 59.9 Design principle for deep soil mixing 934 59.10 References 937 Chapter 60: Foundations subjected to cyclic and dynamic loads 939 M. Srbulov and A. S. O’Brien 60.1 Introduction 939 60.2 Cyclic loading 939 60.3 Earthquake effects 940 60.4 Offshore foundation design 948 60.5 Machine foundations 950 60.6 References 951 SECTION 6: Design of retaining structures 955 Section Editor: A. Gaba Chapter 61: Introduction to Section 6 957 A. Gaba Chapter 62: Types of retaining walls 959 S. Anderson 62.1 Introduction 959 62.2 Gravity walls 959 62.3 Embedded walls 961 62.4 Hybrid walls 966 62.5 Comparison of walls 966 62.6 References 968 Chapter 63: Principles of retaining wall design 969 M. Devriendt 63.1 Introduction 969 63.2 Design concepts 969 63.3 Selection of design parameters 973 63.4 Ground movements and their prediction 977 63.5 Principles of building damage assessment 979 63.6 References 980 Chapter 64: Geotechnical design of retaining walls 981 A. Pickles 64.1 Introduction 981 64.2 Gravity walls 981 64.3 Reinforced soil walls 988 64.4 Embedded walls 988 64.5 References 999 Chapter 65: Geotechnical design of retaining wall support systems 1001 S. Anderson 65.1 Introduction 1001 65.2 Design requirements and performance criteria 1001 65.3 Types of wall support systems 1002 65.4 Props 1003 65.5 Tied systems 1005 65.6 Soil berms 1006 65.7 Other systems of wall support 1008 65.8 References 1009 Chapter 66: Geotechnical design of ground anchors 1011 M. Turner 66.1 Introduction 1011 66.2 Review of design responsibilities 1014 66.3 The design of ground anchors for the support of retaining walls 1015 66.4 Detailed design of ground anchors 1017 66.5 References 1029 Chapter 67: Retaining walls as part of complete underground structure 1031 P. Ingram 67.1 Introduction 1031 67.2 Interfaces with structural design and other disciplines 1031 67.3 Resistance to lateral actions 1033 67.4 Resistance to vertical actions 1034 67.5 Design of bored piles and barrettes to support/resist vertical loading beneath base slab 1036 67.6 References 1037 SECTION 7: Design of earthworks, slopes and pavements 1039 Section Editor: Paul A. Nowak Chapter 68: Introduction to Section 7 1041 P. A. Nowak Chapter 69: Earthworks design principles 1043 P. A. Nowak 69.1 Historical perspective 1043 69.2 Fundamental requirements of earthworks 1043 69.3 Development of analysis methods 1044 69.4 Factors of safety and limit states 1044 69.5 References 1046 Chapter 70: Design of new earthworks 1047 P. A. Nowak 70.1 Failure modes 1047 70.2 Typical design parameters 1050 70.3 Pore pressures and groundwater 1053 70.4 Loadings 1055 70.5 Vegetation 1057 70.6 Embankment construction 1058 70.7 Embankment settlement and foundation treatment 1059 70.8 Instrumentation 1062 70.9 References 1063 Chapter 71: Earthworks asset management and remedial design 1067 B. T. McGinnity and N. Saffari 71.1 Introduction 1067 71.2 Stability and performance 1069 71.3 Earthwork condition appraisal, risk mitigation and control 1073 71.4 Maintenance and remedial works 1075 71.5 References 1085 Chapter 72: Slope stabilisation methods 1087 P. A. Nowak 72.1 Introduction 1087 72.2 Embedded solutions 1087 72.3 Gravity solutions 1088 72.4 Reinforced/nailed solutions 1089 72.5 Slope drainage 1090 72.6 References 1091 Chapter 73: Design of soil reinforced slopes and structures 1093 S. Manceau, C. Macdiarmid and G. Horgan 73.1 Introduction and scope 1093 73.2 Reinforcement types and properties 1093 73.3 General principles of reinforcement action 1094 73.4 General principles of design 1096 ICE__MGE_Prelims_Vol 2.indd vi ICE__MGE_Prelims_Vol 2.indd vi 1/13/2012 11:16:47 AM 1/13/2012 11:16:47 AM ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com vii Contents – volume II ice | manuals Chapter 80: Groundwater control 1173 M. Preene 80.1 Introduction 1173 80.2 Objectives of groundwater control 1173 80.3 Methods of groundwater control 1175 80.4 Groundwater control by exclusion 1175 80.5 Groundwater control by pumping 1176 80.6 Design issues 1185 80.7 Regulatory issues 1188 80.8 References 1189 Chapter 81: Types of bearing piles 1191 S. Wade, R. Handley and J. Martin 81.1 Introduction 1191 81.2 Bored piles 1192 81.3 Driven piles 1206 81.4 Micro-piles 1217 81.5 References 1222 Chapter 82: Piling problems 1225 V. Troughton and J. Hislam 82.1 Introduction 1225 82.2 Bored piles 1226 82.3 Driven piles 1230 82.4 Identifying and resolving problems 1233 82.5 References 1235 Chapter 83: Underpinning 1237 T. Jolley 83.1 Introduction 1237 83.2 Types of underpinning 1237 83.3 Factors infl uencing the choice of underpinning type 1240 83.4 Bearing capacity of underpinning and adjacent footings 1241 83.5 Shoring 1242 83.6 Underpinning in sands and gravel 1243 83.7 Dealing with groundwater 1243 83.8 Underpinning in relation to subsidence settlement 1245 83.9 Safety aspects of underpinning 1245 83.10 Financial aspects 1246 83.11 Conclusion 1246 83.12 References 1246 Chapter 84: Ground improvement 1247 C. J. Serridge and B. Slocombe 84.1 Introduction 1247 84.2 Vibro techniques (vibrocompaction and vibro stone columns) 1247 84.3 Vibro concrete columns 1259 84.4 Dynamic compaction 1261 84.5 References 1268 Chapter 85: Embedded walls 1271 R. Fernie, D. Puller and A. Courts 85.1 Introduction 1271 85.2 Diaphragm walls 1271 85.3 Secant pile walls 1276 85.4 Contiguous pile walls 1280 85.5 Sheet pile walls 1280 85.6 Combi steel walls 1284 85.7 Soldier pile walls (king post or Berlin walling) 1285 85.8 Other wall types 1287 85.9 References 1288 Chapter 86: Soil reinforcement construction 1289 C. Jenner 86.1 Introduction 1289 86.2 Pre-construction 1289 86.3 Construction 1290 86.4 Post-construction 1294 86.5 References 1294 73.5 Reinforced soil walls and abutments 1097 73.6 Reinforced soil slopes 1102 73.7 Basal reinforcement 1104 73.8 References 1106 Chapter 74: Design of soil nails 1109 M. J. Whitbread 74.1 Introduction 1109 74.2 History and development of soil nailing techniques 1109 74.3 Suitability of ground conditions for soil nailing 1109 74.4 Types of soil nails 1110 74.5 Behaviour of soil nails 1110 74.6 Design 1110 74.7 Construction 1112 74.8 Drainage 1113 74.9 Corrosion of soil nails 1113 74.10 Testing soil nails 1113 74.11 Maintenance of soil nailed structures 1113 74.12 References 1113 Chapter 75: Earthworks material specifi cation, compaction and control 1115 P. G. Dumelow 75.1 The earthworks specifi cation 1115 75.2 Compaction 1124 75.3 Compaction plant 1128 75.4 Control of earthworks 1130 75.5 Compliance testing of earthworks 1132 75.6 Managing and controlling specifi c materials 1135 75.7 References 1141 Chapter 76: Issues for pavement design 1143 P. Coney, P. Gilbert and Reviewed by P. Fleming 76.1 Introduction 1143 76.2 Purpose of pavement foundation 1144 76.3 Pavement foundation theory 1145 76.4 Brief recent history of pavement foundation design 1145 76.5 Current design standards 1146 76.6 Sub-grade assessment 1150 76.7 Other design issues 1152 76.8 Construction specifi cation 1153 76.9 Conclusion 1154 76.10 References 1154 SECTION 8: Construction processes 1157 Section Editor: T. P. Suckling Chapter 77: Introduction to Section 8 1159 T. P. Suckling Chapter 78: Procurement and specifi cation 1161 T. P. Suckling 78.1 Introduction 1161 78.2 Procurement 1161 78.3 Specifi cations 1163 78.4 Technical issues 1164 78.5 References 1165 Chapter 79: Sequencing of geotechnical works 1167 M. Pennington and T. P. Suckling 79.1 Introduction 1167 79.2 Design construction sequence 1167 79.3 Site logistics 1168 79.4 Safe construction 1168 79.5 Achieving the technical requirements 1170 79.6 Monitoring 1172 79.7 Managing changes 1172 79.8 Common problems 1172 ICE__MGE_Prelims_Vol 2.indd vii ICE__MGE_Prelims_Vol 2.indd vii 2/10/2012 7:06:30 PM 2/10/2012 7:06:30 PM viii www.icemanuals.com ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers Contents – volume II ice | manuals Chapter 94: Principles of geotechnical monitoring 1363 J. Dunnicliff, W. A. Marr and J. Standing 94.1 Introduction 1363 94.2 Benefi ts of geotechnical monitoring 1363 94.3 Systematic approach to planning monitoring programmes using geotechnical instrumentation 1366 94.4 Example of a systematic approach to planning a monitoring programme: using geotechnical instrumentation for an embankment on soft ground 1370 94.5 General guidelines on execution of monitoring programmes 1372 94.6 Summary 1376 94.7 References 1376 Chapter 95: Types of geotechnical instrumentation and their usage 1379 J. Dunnicliff 95.1 Introduction 1379 95.2 Instruments for monitoring groundwater pressure 1379 95.3 Instruments for monitoring deformation 1384 95.4 Instruments for monitoring load and strain in structural members 1389 95.5 Instruments for monitoring total stress 1392 95.6 General role of instrumentation, and summaries of instruments to be considered for helping to provide answers to various geotechnical questions 1393 95.7 Acknowledgement 1400 95.8 References 1402 Chapter 96: Technical supervision of site works 1405 S. Glover and J. Chew 96.1 Introduction 1405 96.2 Reasons for supervision of geotechnical works 1406 96.3 Preparing for a site role 1408 96.4 Managing the site works 1410 96.5 Health and safety responsibilities 1414 96.6 Supervision of site investigation works 1414 96.7 Supervision of piling works 1416 96.8 Supervision of earthworks 1417 96.9 References 1418 Chapter 97: Pile integrity testing 1419 S. French and M. Turner 97.1 Introduction 1419 97.2 The history and development of non-destructive pile testing 1420 97.3 A Review of defects in piles in the context of NDT 1421 97.4 Low-strain integrity testing 1422 97.5 Cross-hole sonic logging 1437 97.6 Parallel seismic testing 1442 97.7 High-strain integrity testing 1442 97.8 The reliability of pile integrity testing 1443 97.9 Selection of a suitable test method 1448 97.10 References 1448 Chapter 98: Pile capacity testing 1451 M. Brown 98.1 An introduction to pile testing 1451 98.2 Static pile testing 1452 98.3 Bi-directional pile testing 1458 98.4 High strain dynamic pile testing 1460 98.5 Rapid load testing 1463 98.6 Pile testing safety 1467 98.7 Simple overview of pile testing methods 1467 98.8 Acknowledgements 1468 98.9 References 1468 Chapter 99: Materials and material testing for foundations 1471 S. Pennington 99.1 Introduction 1471 99.2 Eurocodes 1471 99.3 Materials 1471 99.4 Verifi cation 1472 99.5 Concrete 1472 Chapter 87: Rock stabilisation 1295 R. Nicholson 87.1 Introduction 1295 87.2 Management solutions 1296 87.3 Engineered solutions 1297 87.4 Maintenance requirements 1301 87.5 References 1302 Chapter 88: Soil nailing construction 1303 P. Ball and M. R. Gavins 88.1 Introduction 1303 88.2 Planning 1303 88.3 Slope/site preparation 1305 88.4 Drilling 1306 88.5 Placing the soil nail reinforcement 1306 88.6 Grouting 1307 88.7 Completion/fi nishing 1307 88.8 Slope facing 1308 88.9 Drainage 1310 88.10 Testing 1311 88.11 References 1312 Chapter 89: Ground anchors construction 1313 J. Judge 89.1 Introduction 1313 89.2 Applications of ground anchors 1313 89.3 Types of ground anchors 1314 89.4 Ground anchor tendons 1315 89.5 Construction methods in various ground types 1316 89.6 Ground anchor testing and maintenance 1320 89.7 References 1321 Chapter 90: Geotechnical grouting and soil mixing 1323 A. L. Bell 90.1 Introduction and background 1323 90.2 Permeation grouting in soils 1324 90.3 Soilfracture and compensation grouting 1327 90.4 Compaction grouting 1328 90.5 Jet grouting 1330 90.6 Soil mixing 1333 90.7 Verifi cation for grouting and soil mixing 1338 90.8 References 1340 Chapter 91: Modular foundations and retaining walls 1343 C. Wren 91.1 Introduction 1343 91.2 Modular foundations 1344 91.3 Off-site manufactured solutions – the rationale 1344 91.4 Pre-cast concrete systems 1345 91.5 Modular retaining structures 1349 91.6 References 1349 SECTION 9: Construction verifi cation 1351 Section Editor: M. Brown and M. Devriendt Chapter 92: Introduction to Section 9 1353 M. Devriendt and M. Brown Chapter 93: Quality assurance 1355 D. Corke and T. P. Suckling 93.1 Introduction 1355 93.2 Quality management systems 1355 93.3 Geotechnical specifi cations 1355 93.4 Role of the resident engineer 1356 93.5 Self-certifi cation 1356 93.6 Finding non-conformances 1357 93.7 Forensic investigations 1359 93.8 Conclusions 1360 93.9 References 1361 ICE__MGE_Prelims_Vol 2.indd viii ICE__MGE_Prelims_Vol 2.indd viii 1/13/2012 11:16:47 AM 1/13/2012 11:16:47 AM ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com ix Contents – volume II ice | manuals 100.4 Implementation of planned modifi cations during construction 1497 100.5 ‘Best way out’ approach in OM 1499 100.6 Concluding remarks 1500 100.7 References 1500 Chapter 101: Close-out reports 1503 R. Lindsay and M. Kemp 101.1 Introduction 1503 101.2 Reasons for writing close-out reports 1503 101.3 Contents of close-out report 1505 101.4 Reporting on quality issues 1506 101.5 Reporting on health and safety issues 1506 101.6 Documentation systems and preserving data 1507 101.7 Summary 1507 101.8 References 1507 Index to volumes I and II 1509 99.6 Steel and cast iron 1475 99.7 Timber 1477 99.8 Geosynthetics 1478 99.9 The ground 1479 99.10 Aggregates 1481 99.11 Grout 1482 99.12 Drilling muds 1483 99.13 Miscellaneous materials 1484 99.14 Re-use of foundations 1485 99.15 References 1486 Chapter 100: Observational method 1489 D. Patel 100.1 Introduction 1489 100.2 Fundamentals of OM implementation and pros and cons of its use 1491 100.3 OM concepts and design 1492 ICE__MGE_Prelims_Vol 2.indd ix ICE__MGE_Prelims_Vol 2.indd ix 2/10/2012 7:06:30 PM 2/10/2012 7:06:30 PM Section 5: Design of foundations Section editor: Anthony S. O'Brien ICE_MGE_Ch51.indd 729 ICE_MGE_Ch51.indd 729 1/13/2012 10:33:21 AM 1/13/2012 10:33:21 AM ice | manuals ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com 731 doi: 10.1680/moge.57098.0731 Figure 51.1 outlines the layout and contents of Section 5 Design of foundations. Foundation design is usually divided into two broad cat- egories: shallow and deep, and these categories are also used here. In modern foundation engineering it is helpful to con- sider a third category: hybrid. Hybrid foundations have their own unique features, although their design usually requires an assessment of both shallow and deep foundation behaviour. Examples of hybrid foundations include deep ground improve- ment and piled rafts. The fi nal set of topics, special issues, include building on fi lls, the infl uence of global ground movements on deep foundations, and foundations subject to cyclic and dynamic loading, including earthquakes. In common with other sections of this manual, this section is intended to provide guidance to practising engineers. Given the enormous breadth of the subject and the vast range of ground conditions and structures which a foundation designer may encounter, this section cannot, within the available space, be completely comprehensive. The intent is to outline: the f ■ undamental principles of good design practice; the key mechanisms of ground and ground–structure interaction ■ behaviour which need to be considered; Chapter 51 Introduction to Section 5 Anthony S. O’Brien Mott MacDonald, Croydon, UK Figure 51.1 Layout of chapters in Section 5 Design of foundations Related topics Context and fundamental ground behaviour Sections 1, 2 and 3 Related topics Site investigation Section 4 Construction processes and verification Sections 8 and 9 Foundation types and conceptual design principles Selecting the appropriate foundation type Chapter 52 Shallow foundations Chapter 53 Deep foundations Special issues Hybrid foundations Global ground movements and effects on piles Chapter 57 Building on fills Chapter 58 Pile groups Single piles Chapter 54 Chapter 55 Rafts and piled rafts Chapter 56 Chapter 59 Design principles for ground improvement Rafts Strip and pad footings Chapter 60 Foundations subject to cyclic and dynamic loads ICE_MGE_Ch51.indd 731 ICE_MGE_Ch51.indd 731 2/10/2012 6:23:10 PM 2/10/2012 6:23:10 PM Design of foundations 732 www.icemanuals.com ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers commonly used design methods; ■ the need to integrate a range of specialist disciplines at different ■ stages of the design process; and to provide: references for detailed study; ■ some brief case histories which highlight key issues. ■ A quote from Terzaghi (1936) is particularly pertinent: Whoever expects from soil mechanics a set of simple, hard and fast rules for settlement computations will be deeply dis- appointed…The nature of the problem strictly precludes such rules. Hence, it is essential for the foundation designer to think care- fully about the likely deformation and failure mechanisms which may occur both during and after construction; then compile a checklist of questions which need to be considered and answered. There have been enormous developments in founda- tion engineering during the last few decades. Despite these developments, failures still regularly occur and there are also numerous examples of grossly overconservative design and poor construction practice. There are several commercial and technical factors that can cause these problems. Technically, it is important to: (i) Recognise that foundation engineering is a ‘process’, and that success depends on a series of interlinked activities during both design and construction. (ii) Have a coherent approach to ground risk management; the ‘geotechnical triangle’ is a valuable framework in this context. An understanding of the site’s history and its groundwater regime are critically important. (iii) Have good communication across different design/con- struction teams. (iv) Develop a good understanding of ground–structure interac- tion. It is vitally important for geotechnical and structural engineers to have early two-way discussions, so that the overall behaviour of the proposed works are understood. In particular, the best opportunity for economic founda- tion design is to set realistic (rather than arbitrary and usu- ally overconservative) limits on foundation movement. (v) Have a good awareness of relevant case histories of past foundation performance, and to carefully assess the rel- evant parameters for assessing stability – and in particu- lar, foundation deformation. Sophisticated analysis is not a substitute for a proper selection of design parameters, based on well designed and supervised ground investigations. Chapter 9 Foundation design decisions provides an introduc- tion to these themes, and these are developed in more detail throughout Section 5. Although it is a simplifi cation, it is fair to state that routine ground investigation and analysis methods can lead to: (i) overconservative design of foundations in heavily over- consolidated soils, such as stiff clays; (ii) unsafe foundation design in normally and lightly overcon- solidated soils, such as soft clays. Modern developments in ground investigation and geotechni- cal analysis can avoid these problems, although these modern techniques are still under-used across the civil engineering industry. The chapters in Section 5 highlight some of the devel- opments which are mature enough to be used more routinely. It is hoped that Section 5 will stimulate an improvement in foundation design practice. ICE_MGE_Ch51.indd 732 ICE_MGE_Ch51.indd 732 2/10/2012 6:23:10 PM 2/10/2012 6:23:10 PM ice | manuals ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com 733 doi: 10.1680/moge.57098.0733 CONTENTS 52.1 Introduction 733 52.2 Foundation types 734 52.3 Foundation selection – conceptual design principles 735 52.4 Allowable foundation movement 747 52.5 Design bearing pressures 752 52.6 Parameter selection, introductory comments 754 52.7 Foundation selection – a brief case history 759 52.8 Overall conclusions 763 52.9 References 763 52.1 Introduction This chapter outlines the types of foundation that are com- monly used, together with the key factors which need to be considered before selecting a particular foundation type. Foundation engineering requires a working knowledge of: geotechnical engineering; ■ construction methods; ■ ground-structure interaction. ■ Professor Peck (1962) outlined the three areas of knowledge that are needed in geotechnical engineering: (i) a knowledge of precedents, i.e. a knowledge of case histories; (ii) a working knowledge of geology; (iii) familiarity with soil mechanics. In the vast majority of cases, a foundation design is developed on the basis of an appreciation of the site geology, the nature of the proposed structure and any particular site constraints. The role of analysis is then to check that a proposed foundation design will be acceptable. Although analysis is important it is just one part of the overall design process. Many young civil engineers will have some knowledge of (iii), but it is important that they endeavour to develop their knowledge of (i) and (ii) above. A knowledge of geology (and hydrogeology) is critically important, since it enables many of the risks associated with foundation engineering at a particular site to be assessed. Simplifying assumptions have to be made before any analysis can be carried out (this includes sophisti- cated computer modelling). The site geology and hydrogeol- ogy have to be considered and understood, as early as possible in the project. Discussions should be held with an experienced geologist. Relevant technical literature and, particularly, local case histories should be reviewed. Once this has been done then the appropriateness, or not, of certain assumptions inher- ent in a particular method of calculation can be judged, and the likely errors associated with the predictions from calculations can be assessed. A knowledge of case histories is probably the most important of the three attributes, since this enables the engineer to have an understanding of: (i) what has worked, or not, in the past; (ii) the consequences of particular construction activities on subsequent performance; (iii) past performance, against which the reliability of differ- ent methods of analysis can be compared; (iv) when a proposed activity is going beyond what has been attempted before – this will then require a special effort and expert advice in order to safely develop the design. A foundation is a structural member and supports a superstruc- ture. So an awareness of the sources and nature of structural loads, the structure’s tolerance of foundation movements, and an understanding of ground–structure interaction is also needed. Finally, the foundations must be built economically and safely. Hence, a designer needs to have an appreciation of construc- tion methods and equipment, in order to develop a design that is practical to build. This list of attributes, which a foundation designer needs to possess, is rather intimidating. The author has not yet come across the god-like creature who possesses a perfect knowledge of all these topics. Therefore, fi rst and foremost, the foundation designer must be prepared to ask questions and discuss these with other design and construction specialists (e.g. geologists, structural and material engineers, specialist sub-contractors, etc.). Good foundation design is usually the result of a multi- disciplinary team effort, where two-way communications across the team occur regularly and frequently. Chapter 52 Foundation types and conceptual design principles Anthony S. O’Brien Mott MacDonald, Croydon, UK The main types of foundation include: shallow foundations (pad, strip, raft); deep foundations (piles, caissons, barettes) and hybrid foundations (deep ground improvement, piled rafts). Foundation engineering requires a broad range of skills, from an appreciation of geology and hydrogeology to structural engineering. The performance of foundations is dependent not only on how they are designed, but also on how they are constructed. The overall design process needs to be well managed, to ensure that there are good communications between different design teams and between design and construction. To provide a framework for selecting the most appropriate type of foundation, a useful mnemonic is ‘the 5 S’s’: S – Soil; S – Structure; S – Site; S – Safety; S – Sustainability The magnitude of allowable foundation movement is a key factor in determining the type, size and cost of foundations, and this chapter provides guidance on routine limits. Parameter selection is a common pitfall, and the critical information requirements are described. ICE_MGE_Ch52.indd 733 ICE_MGE_Ch52.indd 733 2/10/2012 6:28:22 PM 2/10/2012 6:28:22 PM Design of foundations 734 www.icemanuals.com ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers 52.2 Foundation types There are two generic types of foundation: shallow and deep. Foundations developed on improved ground can be considered to be a hybrid of both shallow and deep foundations, although ground improvement design requires additional considerations. The advantages and disadvantages of different foundation types are outlined in Table 52.1. (1) Shallow foundations: these typically comprise pad, strip or raft foundations; refer to Figure 52.1. Pad foundations, Figure 52.1(a), may be square, circular or rectangular. A pad foundation usually only supports one or two col- umns. Strip foundations (Figure 52.1(b)) are commonly used to provide support to a load-bearing wall or for sev- eral closely spaced columns. The length of a strip foun- dation is much greater than its width. A raft foundation (Figure 52.1(c)) could support the entire structure or a substantial part of it. A ‘compensated’ raft (also known as a ‘buoyant’ raft) is a special type of raft. It includes a void, thereby reducing the ‘net’ increase in bearing pressure (section 52.5) on the ground below the foundation. This will increase the factor of safety against bearing capacity failure and reduce foundation settlement, compared with a conventional raft. The structural form of shallow founda- tions can vary, but pad and strip foundations could com- prise either mass concrete or reinforced concrete, whereas raft foundations usually comprise reinforced concrete. The soil resistance to the loads applied by the structure are predominantly developed by the near-surface soil below the base of the foundation. Shallow foundations are usu- ally constructed using simple excavation plant and general labour. Tomlinson et al. (1987) gives useful advice on rou- tine foundation design for low-rise buildings. (2) Deep foundations: for the majority of routine structures, deep foundations comprise piles; refer to Figure 52.2. There are numerous different types of pile, discussed in Chapter 54 Single piles although piles are usually classifi ed as either driven or bored. Pile construction is a specialist activity and should only be carried out by contractors who have the appropriate equipment and experience. The layout of pile foundations can vary substantially from a single pile below a load-bearing column, to a large number of piles in a group supporting the entire structure, via a pile cap (which transfers load from the structure directly into the piles). For a conventionally designed pile group, it is assumed that the piles carry the entire load. Deep foundations also include barettes, shafts or cais- sons, which tend to be bespoke foundations for special circumstances. Caissons, barettes and shafts typically have a large diameter or cross-sectional area relative to their depth in comparison with conventional piles. Barettes are rectangular in plan, and are installed using diaphragm-wall construction techniques. Both shafts and caissons are circular in plan; however, they are usually constructed by different methods. Shafts could be hand- dug or excavated using back-actors, with excavation sup- port installed top-down, using pre-cast concrete rings or cast-in situ concrete lining. Caissons are usually jacked or sunk into place using combinations of kentledge, excava- tion and perimeter lubrication (using bentonite). For both piled foundations and deep shafts the load transfer to the ground is via shear along the vertical sides of the shaft or pile and by end-bearing resistance. Piled rafts are a hybrid type of foundation with the struc- tural load being transferred to the soil via the raft (as for a shallow foundation) and the piles (as for a deep foundation). The principal difference between a piled raft and a conven- tional pile group is that the piles are designed to mobilise most of their ultimate load-bearing resistance and act as settlement-reducing elements whilst the raft provides the appropriate overall factor of safety against bearing capacity failure. Compared with a conventional pile group, a piled raft has a relatively small number of widely spaced piles (Figure 52.3). Piled-raft design requires specialist input. (3) Foundations on improved ground: in general, the pur- pose of ground improvement is to increase the strength and stiffness of the ground below a proposed structure, and then shallow structural foundations are constructed on the surface of the improved ground (Figure 52.4). Below the structural foundations, a granular layer (some- times reinforced with geogrids) is often used to transfer loads into the reinforcing elements (Figure 52.4). The mechanism of ground improvement is usually either: (i) Mass reinforcement – usually for clays, silts or made ground. A large number of stiff elements are intro- duced into the compressible layer. (ii) Densifi cation – usually for sands or gravels. A com- paction process forces a rearrangement of the soil particles into a denser state. Reinforcement: techniques such as vibro stone columns or deep soil mixing facilitate the replacement of soft com- pressible materials by stronger materials introduced into the ground via specialist equipment. These stronger elements carry most of the foundation load. However, the remaining soft compressible materials will also carry some of the foun- dation loads, hence the term ‘reinforcement’. It is important to note that the reinforcing elements usually have negligible tensile and bending resistance. Sometimes reinforcing ele- ments such as stone columns are called ‘stone piles’; how- ever, this is quite incorrect and misleading. Foundations built upon improved ground will behave in a quite different manner to piled foundations (Figure 52.5). Densifi cation: soils such as loose sand with a low silt or clay content can be compacted into a denser state. Once den- sifi ed the sand will be a more competent stratum and be able to carry the foundation loads directly. Hence, conventional shallow foundations can be placed on the densifi ed layer. ICE_MGE_Ch52.indd 734 ICE_MGE_Ch52.indd 734 2/10/2012 6:28:22 PM 2/10/2012 6:28:22 PM Foundation types and conceptual design principles ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com 735 Densifi cation may be carried out via a wide range of spe- cialist equipment. The key issue for densifi cation projects is usually the relative density that can be achieved compared with the value which is needed to ensure that foundation settlement is acceptable. The success of ground improvement (both by reinforce- ment or densifi cation) is sensitive to the nature of the soil profi le and the soil macrofabric. For example, densifi cation by vibrocompaction may be straightforward if the sand is homogeneous and has a low silt or clay content. Compaction will be much more diffi cult and often less effective if there are numerous bands of silt or clay in the sand. These soil features can be easily missed by conventional boreholes and sampling at discrete depth intervals. Continuous sampling or profi ling techniques (such as static cone penetration testing, CPTs) are usually very benefi cial when designing ground improvement. Similar considerations can apply to reinforce- ment techniques. Quality control and fi eld testing in order to verify the effectiveness of ground improvement are a signifi - cant component of any ground-improvement project. 52.3 Foundation selection – conceptual design principles 52.3.1 Information requirements and the foundation design process Figure 52.6 outlines the typical information requirements, the design deliverables (reports, etc.) and the project phases that are followed to design and construct a foundation. During the early stages the key questions are: (1) Site geology, hydrogeology and history: what are the geo- logical age and the depositional environment of the main deposits under the site? What subsequent changes may have occurred (e.g. landslides, man’s infl uence)? (2) What will be built?: form of structure, likely construction methods, main site constraints, applied loads, principal constraints (e.g. allowable structural movements)? (3) Engineering knowledge: what existing knowledge do we have? For example, relevant technical literature, good case histories, local customs and experience or expertise. This collation of available data into a desk study report is an important and cost-effective means of managing ground risks on a project. Sole reliance on boreholes in the absence of a proper desk study is potentially very dangerous. The main ground hazards can be identifi ed from the desk study and the key fea- tures of ground behaviour can be assessed. This will inform the design of intrusive ground investigation (refer to Chapters 40 The ground as a hazard, 41 Man-made hazards and obstructions, 43 Preliminary studies and 44 Planning, procurement and manage- ment). It is often the case that designers ‘inherit’ ground inves- tigation reports from previous or adjacent projects and studies. It is very important that the scope, adequacy and reliability of this information are assessed in the context of the current project requirements. If the structure has been relocated, or more oner- ous loading or allowable movement criteria are required, then an additional ground investigation may be needed (perhaps using more sophisticated investigation techniques). Foundation design is an iterative process. Once relevant information has been obtained for the site, the key data should Superstructure column Bearing wall (or multiple colomns) Ground surface Ground surface (a) (b) (c) (d) Pad Strip Raft ‘Compensated’ raft Entire structure Entire structure Void B L B B T D D T Figure 52.1 Types of shallow foundations ICE_MGE_Ch52.indd 735 ICE_MGE_Ch52.indd 735 2/10/2012 6:28:22 PM 2/10/2012 6:28:22 PM Design of foundations 736 www.icemanuals.com ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers Figure 52.2 Deep foundation, conventional pile group Figure 52.3 Hybrid foundation, piled raft Original soil (uncompacted) Shallow foundation, raft or strip foundations Ground mass, densified Ground mass, densified beneath foundations beneath foundations Ground mass, densified beneath foundations Ground mass, Ground mass, reinforced beneath reinforced beneath foundations foundations Ground mass, reinforced beneath foundations Most of foundation load taken by reinforcing elements Lateral confinement by natural ground (?) (a) Ground improvement by densification (b) Ground improvement by reinforcement Some foundation load resisted by natural ground Ground surface Ground surface Geogrid reinforced granular layer (?) Pad/strip foundations Competent soil layer Competent soil layer Figure 52.4 Hybrid foundation – deep ground improvement be summarised on a plan and vertical cross-sections through and beyond the site boundaries. Drawn to scale, with levels referenced to an appropriate survey datum, as a minimum, the following features should be drawn: (i) the previous and proposed ground surfaces; (ii) any previous and neighbouring structures and under- ground services; (iii) ground profi le, strata boundaries (including selected ground properties from testing); (iv) groundwater levels; (v) outline of the proposed structure and proposed locations for foundations; (vi) list as bullet points, the key site constraints and hazards. Based on a knowledge of the ground profi le, the type of struc- ture and key site constraints, an experienced engineer should be able to identify appropriate conceptual designs for the foun- dations. Analyses would then be carried out to check that this concept had an acceptable level of stability and that foundation movements were acceptable. If these are not acceptable, then the concept would be modifi ed (say, pile foundations would ICE_MGE_Ch52.indd 736 ICE_MGE_Ch52.indd 736 2/10/2012 6:28:23 PM 2/10/2012 6:28:23 PM

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ICE manual of geotechnical engineering Volume 2 Geotechnical Design, Construction and Verification Edited by John Burland Imperial College London, UK Tim Chapman Arup Geotechnics, UK Hilary Skinner Donaldson Associates Ltd, UK Michael Brown University of Dundee, UK ice | manuals ICE__MGE_Prelims_Vol 2.indd iii ICE__MGE_Prelims_Vol 2.indd iii 2/10/2012 7:06:30 PM 2/10/2012 7:06:30 PM Published by ICE Publishing, 40 Marsh Wall, London E14 9TP, UK www.icevirtuallibrary.com Full details of ICE Publishing sales representatives and distributors can be found at: www.icevirtuallibrary.com/info/printbooksales First published 2012 Future titles in the ICE Manuals series from ICE Publishing ICE manual of structural design ICE manual of project management Currently available in the ICE Manual series from ICE Publishing ICE manual of bridge engineering – second edition. 978-0-7277-3452-5 ICE manual of construction materials – two volume set. 978-0-7277-3597-3 ICE manual of health and safety in construction. 978-0-7277-4056-4 ICE manual of construction law. 978-0-7277-4087-8 ICE manual of highway design and management. 978-0-7277-4111-0 www.icemanuals.com A catalogue record for this book is available from the British Library ISBN: 978-0-7277-5707-4 (volume I) ISBN: 978-0-7277-5709-8 (volume II) ISBN: 978-0-7277-3652-9 (two volume set) © Institution of Civil Engineers 2012 ICE Publishing is a division of Thomas Telford Ltd, a wholly owned subsidiary of the Institution of Civil Engineers (ICE). All rights, including translation, reserved Except as permitted by the Copyright, Designs and Patents Act 1988, no part of this publication may be reproduced, stored in a retrieval system or transmitted in any form or by any means, electronic, mechanical, photocopying or otherwise, without the prior written permission of the Publisher, ICE Publishing, 40 Marsh Wall London E14 9TP, UK. This book is published on the understanding that the authors are solely responsible for the statements made and opinions expressed in it and that its publication does not necessarily imply that such statements and/or opinions are or refl ect the views or opinions of the publishers. While every effort has been made to ensure that the statements made and the opinions expressed in this publication provide a safe and accurate guide, no liability or responsibility can be accepted in this respect by the authors or publishers. The authors and the publisher have made every reasonable effort to locate, contact and acknowledge copyright owners. The publisher wishes to be informed by copyright owners who are not properly identifi ed and acknowledged in this publication so that we may make necessary corrections. Permission to reproduce extracts from British Standards is granted by the British Standard Institution (BSI), www.bsigroup.com. No other use of this material is permitted. British Standards can be obtained from the BSI online shop: http://shop.bsigroup.com. Typeset by Newgen Imaging Sytems Pvt. Ltd., Chennai, India Printed and bound in Great Britain by Bell & Bain Ltd, Glasgow ICE__MGE_Prelims_Vol 2.indd iv ICE__MGE_Prelims_Vol 2.indd iv 1/11/2012 2:29:28 PM 1/11/2012 2:29:28 PM ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com xiii Preface We began to formulate the initial ideas for this Manual as early as 2006. It had become apparent to us that civil and structural engineers not specialising in geotechnics face a daunting knowledge gap when they come up against a geotechnical problem. Most civil engineers leave university with very little grounding in geotechnical engineering. They will have a fair grasp of applied mechanics (mainly aimed at structural engineering). They will have had a basic introduction to geology and they will have studied the elements of soil mechanics and rock mechanics. But a recent graduate usually lacks a coherent understanding of the approach to, and methods of, geotechnical engineering and how these differ from other more widely prac- tised branches of engineering. A survey carried out by ICE Publishing showed that information tends to be obtained from a wide range of sources through word of mouth, the internet and various publications. For the young practitioner this leads to a fragmented approach. Much of the geotechnical material is written by specialists for specialists and its ad hoc application by a general practitioner is often inappropriate and can be extremely dangerous. We felt that it would be of great benefi t to our profession to provide a single fi rst- port-of-call authoritative reference source aimed at informing the less experienced engineer. To our delight this concept was endorsed by the ICE Best Practice Panel and the British Geotechnical Association and has offered a unique opportunity to provide authoritative guidance within a coherent framework of good geotech- nical engineering. This ICE Manual of Geotechnical Engineering has been a labour of love! The contribution of 99 contributors and 10 section editors has made it possible to distil a great deal of experience from the profession into the books you see here. Don’t imagine this will cover everything that a geotechnical engineer will face in their career – but it provides a “starting point” from which to build experience whilst remaining grounded in robust fundamentals. As mentioned previously, the Manual is aimed at people in the early stage of their careers who need a readily accessible source of information when working in new aspects of geotechnical engineering. However it is expected that it also should prove valuable to all geotechnical engineering professionals. The aim has been to produce a manual that addresses the practice of geotechnical engineering in the 21st century including contemporary procurement, process and design standards and procedures. The grouping of chapters has been carefully chosen to facilitate a multi-disciplinary and holistic approach to the solution of construction challenges. A key message is the importance of drawing on “well-winnowed experience” for the smooth and reliable execution of projects. Such experience is best gained by working closely with a suitably experienced design or construction team. It is hoped that this Manual will help in the training and development of the next generation of geotechnical engineers and will act as a useful source of reference to those with more experience. The Editors are grateful to all those contributors and section editors who have generously given so much of their time and knowledge in producing such a comprehensive book. John Burland, Tim Chapman, Hilary Skinner and Michael Brown ICE__MGE_Prelims_Vol 2.indd xiii ICE__MGE_Prelims_Vol 2.indd xiii 2/10/2012 7:06:31 PM 2/10/2012 7:06:31 PM ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com v Contents Volume II Foreword and endorsement xi Preface xiii List of contributors xv SECTION 5: Design of foundations 729 Section Editor: A. S. O’Brien Chapter 51: Introduction to Section 5 731 A. S. O’Brien Chapter 52: Foundation types and conceptual design principles 733 A. S. O’Brien 52.1 Introduction 733 52.2 Foundation types 734 52.3 Foundation selection – conceptual design principles 735 52.4 Allowable foundation movement 747 52.5 Design bearing pressures 752 52.6 Parameter selection – introductory comments 754 52.7 Foundation selection – a brief case history 759 52.8 Overall conclusions 763 52.9 References 763 Chapter 53: Shallow foundations 765 A. S. O’Brien and I. Farooq 53.1 Introduction 765 53.2 Causes of foundation movements 765 53.3 Construction processes and design considerations 768 53.4 Applied bearing pressures, foundation layout and interaction effects 773 53.5 Bearing capacity 774 53.6 Settlement 778 53.7 Information requirements and parameter selection 789 53.8 Case history for a prestigious building on glacial tills 796 53.9 Overall conclusions 799 53.10 References 800 Chapter 54: Single piles 803 A. Bell and C. Robinson 54.1 Introduction 803 54.2 Selection of pile type 803 54.3 Axial load capacity (ultimate limit state) 804 54.4 Factors of safety 814 54.5 Pile settlement 814 54.6 Pile behaviour under lateral load 816 54.7 Pile load testing strategy 818 54.8 Defi nition of pile failure 820 54.9 References 820 Chapter 55: Pile-group design 823 A. S. O’Brien 55.1 Introduction 823 55.2 Pile-group capacity 824 55.3 Pile-to-pile interaction: vertical loading 827 55.4 Pile-to-pile interaction: horizontal loading 834 55.5 Simplifi ed methods of analysis 834 55.6 Differential settlement 841 55.7 Time-dependent settlement 841 55.8 Optimising pile-group confi gurations 841 55.9 Information requirements for design and parameter selection 843 55.10 Ductility, redundancy and factors of safety 846 55.11 Pile-group design responsibility 847 55.12 Case history 847 55.13 Overall conclusions 850 55.14 References 850 Chapter 56: Rafts and piled rafts 853 A. S. O’Brien, J. B. Burland and T. Chapman 56.1 Introduction 853 56.2 Analysis of raft behaviour 854 56.3 Structural design of rafts 860 56.4 Design of a real raft 861 56.5 Piled rafts, conceptual design principles 863 56.6 Raft-enhanced pile groups 868 56.7 Pile-enhanced rafts 879 56.8 A case history of a pile-enhanced raft – the Queen Elizabeth II Conference Centre 883 56.9 Key points 884 56.10 References 885 Chapter 57: Global ground movements and their effects on piles 887 E. Ellis and A. S. O’Brien 57.1 Introduction 887 57.2 Negative skin friction 888 57.3 Heave-induced tension 891 57.4 Piles subject to lateral ground movements 893 57.5 Conclusions 897 57.6 References 897 Chapter 58: Building on fi lls 899 H. D. Skinner 58.1 Introduction 899 58.2 Engineering characteristics of fi ll deposits 899 58.3 Investigation of fi lls 900 58.4 Fill properties 902 58.5 Volume changes in fi lls 904 58.6 Design issues 907 58.7 Construction on engineered fi lls 909 58.8 Summary 910 58.9 References 910 ICE__MGE_Prelims_Vol 2.indd v ICE__MGE_Prelims_Vol 2.indd v 2/10/2012 7:06:30 PM 2/10/2012 7:06:30 PM vi www.icemanuals.com ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers Contents – volume II ice | manuals Chapter 59: Design principles for ground improvement 911 R. Essler 59.1 Introduction 911 59.2 General design principles for ground improvement 912 59.3 Design principles for void fi lling 913 59.4 Design principles for compaction grouting 914 59.5 Design principles for permeation grouting 916 59.6 Design principles for jet grouting 924 59.7 Design principles for vibrocompaction and vibroreplacement 929 59.8 Design principles for dynamic compaction 933 59.9 Design principle for deep soil mixing 934 59.10 References 937 Chapter 60: Foundations subjected to cyclic and dynamic loads 939 M. Srbulov and A. S. O’Brien 60.1 Introduction 939 60.2 Cyclic loading 939 60.3 Earthquake effects 940 60.4 Offshore foundation design 948 60.5 Machine foundations 950 60.6 References 951 SECTION 6: Design of retaining structures 955 Section Editor: A. Gaba Chapter 61: Introduction to Section 6 957 A. Gaba Chapter 62: Types of retaining walls 959 S. Anderson 62.1 Introduction 959 62.2 Gravity walls 959 62.3 Embedded walls 961 62.4 Hybrid walls 966 62.5 Comparison of walls 966 62.6 References 968 Chapter 63: Principles of retaining wall design 969 M. Devriendt 63.1 Introduction 969 63.2 Design concepts 969 63.3 Selection of design parameters 973 63.4 Ground movements and their prediction 977 63.5 Principles of building damage assessment 979 63.6 References 980 Chapter 64: Geotechnical design of retaining walls 981 A. Pickles 64.1 Introduction 981 64.2 Gravity walls 981 64.3 Reinforced soil walls 988 64.4 Embedded walls 988 64.5 References 999 Chapter 65: Geotechnical design of retaining wall support systems 1001 S. Anderson 65.1 Introduction 1001 65.2 Design requirements and performance criteria 1001 65.3 Types of wall support systems 1002 65.4 Props 1003 65.5 Tied systems 1005 65.6 Soil berms 1006 65.7 Other systems of wall support 1008 65.8 References 1009 Chapter 66: Geotechnical design of ground anchors 1011 M. Turner 66.1 Introduction 1011 66.2 Review of design responsibilities 1014 66.3 The design of ground anchors for the support of retaining walls 1015 66.4 Detailed design of ground anchors 1017 66.5 References 1029 Chapter 67: Retaining walls as part of complete underground structure 1031 P. Ingram 67.1 Introduction 1031 67.2 Interfaces with structural design and other disciplines 1031 67.3 Resistance to lateral actions 1033 67.4 Resistance to vertical actions 1034 67.5 Design of bored piles and barrettes to support/resist vertical loading beneath base slab 1036 67.6 References 1037 SECTION 7: Design of earthworks, slopes and pavements 1039 Section Editor: Paul A. Nowak Chapter 68: Introduction to Section 7 1041 P. A. Nowak Chapter 69: Earthworks design principles 1043 P. A. Nowak 69.1 Historical perspective 1043 69.2 Fundamental requirements of earthworks 1043 69.3 Development of analysis methods 1044 69.4 Factors of safety and limit states 1044 69.5 References 1046 Chapter 70: Design of new earthworks 1047 P. A. Nowak 70.1 Failure modes 1047 70.2 Typical design parameters 1050 70.3 Pore pressures and groundwater 1053 70.4 Loadings 1055 70.5 Vegetation 1057 70.6 Embankment construction 1058 70.7 Embankment settlement and foundation treatment 1059 70.8 Instrumentation 1062 70.9 References 1063 Chapter 71: Earthworks asset management and remedial design 1067 B. T. McGinnity and N. Saffari 71.1 Introduction 1067 71.2 Stability and performance 1069 71.3 Earthwork condition appraisal, risk mitigation and control 1073 71.4 Maintenance and remedial works 1075 71.5 References 1085 Chapter 72: Slope stabilisation methods 1087 P. A. Nowak 72.1 Introduction 1087 72.2 Embedded solutions 1087 72.3 Gravity solutions 1088 72.4 Reinforced/nailed solutions 1089 72.5 Slope drainage 1090 72.6 References 1091 Chapter 73: Design of soil reinforced slopes and structures 1093 S. Manceau, C. Macdiarmid and G. Horgan 73.1 Introduction and scope 1093 73.2 Reinforcement types and properties 1093 73.3 General principles of reinforcement action 1094 73.4 General principles of design 1096 ICE__MGE_Prelims_Vol 2.indd vi ICE__MGE_Prelims_Vol 2.indd vi 1/13/2012 11:16:47 AM 1/13/2012 11:16:47 AM ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com vii Contents – volume II ice | manuals Chapter 80: Groundwater control 1173 M. Preene 80.1 Introduction 1173 80.2 Objectives of groundwater control 1173 80.3 Methods of groundwater control 1175 80.4 Groundwater control by exclusion 1175 80.5 Groundwater control by pumping 1176 80.6 Design issues 1185 80.7 Regulatory issues 1188 80.8 References 1189 Chapter 81: Types of bearing piles 1191 S. Wade, R. Handley and J. Martin 81.1 Introduction 1191 81.2 Bored piles 1192 81.3 Driven piles 1206 81.4 Micro-piles 1217 81.5 References 1222 Chapter 82: Piling problems 1225 V. Troughton and J. Hislam 82.1 Introduction 1225 82.2 Bored piles 1226 82.3 Driven piles 1230 82.4 Identifying and resolving problems 1233 82.5 References 1235 Chapter 83: Underpinning 1237 T. Jolley 83.1 Introduction 1237 83.2 Types of underpinning 1237 83.3 Factors infl uencing the choice of underpinning type 1240 83.4 Bearing capacity of underpinning and adjacent footings 1241 83.5 Shoring 1242 83.6 Underpinning in sands and gravel 1243 83.7 Dealing with groundwater 1243 83.8 Underpinning in relation to subsidence settlement 1245 83.9 Safety aspects of underpinning 1245 83.10 Financial aspects 1246 83.11 Conclusion 1246 83.12 References 1246 Chapter 84: Ground improvement 1247 C. J. Serridge and B. Slocombe 84.1 Introduction 1247 84.2 Vibro techniques (vibrocompaction and vibro stone columns) 1247 84.3 Vibro concrete columns 1259 84.4 Dynamic compaction 1261 84.5 References 1268 Chapter 85: Embedded walls 1271 R. Fernie, D. Puller and A. Courts 85.1 Introduction 1271 85.2 Diaphragm walls 1271 85.3 Secant pile walls 1276 85.4 Contiguous pile walls 1280 85.5 Sheet pile walls 1280 85.6 Combi steel walls 1284 85.7 Soldier pile walls (king post or Berlin walling) 1285 85.8 Other wall types 1287 85.9 References 1288 Chapter 86: Soil reinforcement construction 1289 C. Jenner 86.1 Introduction 1289 86.2 Pre-construction 1289 86.3 Construction 1290 86.4 Post-construction 1294 86.5 References 1294 73.5 Reinforced soil walls and abutments 1097 73.6 Reinforced soil slopes 1102 73.7 Basal reinforcement 1104 73.8 References 1106 Chapter 74: Design of soil nails 1109 M. J. Whitbread 74.1 Introduction 1109 74.2 History and development of soil nailing techniques 1109 74.3 Suitability of ground conditions for soil nailing 1109 74.4 Types of soil nails 1110 74.5 Behaviour of soil nails 1110 74.6 Design 1110 74.7 Construction 1112 74.8 Drainage 1113 74.9 Corrosion of soil nails 1113 74.10 Testing soil nails 1113 74.11 Maintenance of soil nailed structures 1113 74.12 References 1113 Chapter 75: Earthworks material specifi cation, compaction and control 1115 P. G. Dumelow 75.1 The earthworks specifi cation 1115 75.2 Compaction 1124 75.3 Compaction plant 1128 75.4 Control of earthworks 1130 75.5 Compliance testing of earthworks 1132 75.6 Managing and controlling specifi c materials 1135 75.7 References 1141 Chapter 76: Issues for pavement design 1143 P. Coney, P. Gilbert and Reviewed by P. Fleming 76.1 Introduction 1143 76.2 Purpose of pavement foundation 1144 76.3 Pavement foundation theory 1145 76.4 Brief recent history of pavement foundation design 1145 76.5 Current design standards 1146 76.6 Sub-grade assessment 1150 76.7 Other design issues 1152 76.8 Construction specifi cation 1153 76.9 Conclusion 1154 76.10 References 1154 SECTION 8: Construction processes 1157 Section Editor: T. P. Suckling Chapter 77: Introduction to Section 8 1159 T. P. Suckling Chapter 78: Procurement and specifi cation 1161 T. P. Suckling 78.1 Introduction 1161 78.2 Procurement 1161 78.3 Specifi cations 1163 78.4 Technical issues 1164 78.5 References 1165 Chapter 79: Sequencing of geotechnical works 1167 M. Pennington and T. P. Suckling 79.1 Introduction 1167 79.2 Design construction sequence 1167 79.3 Site logistics 1168 79.4 Safe construction 1168 79.5 Achieving the technical requirements 1170 79.6 Monitoring 1172 79.7 Managing changes 1172 79.8 Common problems 1172 ICE__MGE_Prelims_Vol 2.indd vii ICE__MGE_Prelims_Vol 2.indd vii 2/10/2012 7:06:30 PM 2/10/2012 7:06:30 PM viii www.icemanuals.com ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers Contents – volume II ice | manuals Chapter 94: Principles of geotechnical monitoring 1363 J. Dunnicliff, W. A. Marr and J. Standing 94.1 Introduction 1363 94.2 Benefi ts of geotechnical monitoring 1363 94.3 Systematic approach to planning monitoring programmes using geotechnical instrumentation 1366 94.4 Example of a systematic approach to planning a monitoring programme: using geotechnical instrumentation for an embankment on soft ground 1370 94.5 General guidelines on execution of monitoring programmes 1372 94.6 Summary 1376 94.7 References 1376 Chapter 95: Types of geotechnical instrumentation and their usage 1379 J. Dunnicliff 95.1 Introduction 1379 95.2 Instruments for monitoring groundwater pressure 1379 95.3 Instruments for monitoring deformation 1384 95.4 Instruments for monitoring load and strain in structural members 1389 95.5 Instruments for monitoring total stress 1392 95.6 General role of instrumentation, and summaries of instruments to be considered for helping to provide answers to various geotechnical questions 1393 95.7 Acknowledgement 1400 95.8 References 1402 Chapter 96: Technical supervision of site works 1405 S. Glover and J. Chew 96.1 Introduction 1405 96.2 Reasons for supervision of geotechnical works 1406 96.3 Preparing for a site role 1408 96.4 Managing the site works 1410 96.5 Health and safety responsibilities 1414 96.6 Supervision of site investigation works 1414 96.7 Supervision of piling works 1416 96.8 Supervision of earthworks 1417 96.9 References 1418 Chapter 97: Pile integrity testing 1419 S. French and M. Turner 97.1 Introduction 1419 97.2 The history and development of non-destructive pile testing 1420 97.3 A Review of defects in piles in the context of NDT 1421 97.4 Low-strain integrity testing 1422 97.5 Cross-hole sonic logging 1437 97.6 Parallel seismic testing 1442 97.7 High-strain integrity testing 1442 97.8 The reliability of pile integrity testing 1443 97.9 Selection of a suitable test method 1448 97.10 References 1448 Chapter 98: Pile capacity testing 1451 M. Brown 98.1 An introduction to pile testing 1451 98.2 Static pile testing 1452 98.3 Bi-directional pile testing 1458 98.4 High strain dynamic pile testing 1460 98.5 Rapid load testing 1463 98.6 Pile testing safety 1467 98.7 Simple overview of pile testing methods 1467 98.8 Acknowledgements 1468 98.9 References 1468 Chapter 99: Materials and material testing for foundations 1471 S. Pennington 99.1 Introduction 1471 99.2 Eurocodes 1471 99.3 Materials 1471 99.4 Verifi cation 1472 99.5 Concrete 1472 Chapter 87: Rock stabilisation 1295 R. Nicholson 87.1 Introduction 1295 87.2 Management solutions 1296 87.3 Engineered solutions 1297 87.4 Maintenance requirements 1301 87.5 References 1302 Chapter 88: Soil nailing construction 1303 P. Ball and M. R. Gavins 88.1 Introduction 1303 88.2 Planning 1303 88.3 Slope/site preparation 1305 88.4 Drilling 1306 88.5 Placing the soil nail reinforcement 1306 88.6 Grouting 1307 88.7 Completion/fi nishing 1307 88.8 Slope facing 1308 88.9 Drainage 1310 88.10 Testing 1311 88.11 References 1312 Chapter 89: Ground anchors construction 1313 J. Judge 89.1 Introduction 1313 89.2 Applications of ground anchors 1313 89.3 Types of ground anchors 1314 89.4 Ground anchor tendons 1315 89.5 Construction methods in various ground types 1316 89.6 Ground anchor testing and maintenance 1320 89.7 References 1321 Chapter 90: Geotechnical grouting and soil mixing 1323 A. L. Bell 90.1 Introduction and background 1323 90.2 Permeation grouting in soils 1324 90.3 Soilfracture and compensation grouting 1327 90.4 Compaction grouting 1328 90.5 Jet grouting 1330 90.6 Soil mixing 1333 90.7 Verifi cation for grouting and soil mixing 1338 90.8 References 1340 Chapter 91: Modular foundations and retaining walls 1343 C. Wren 91.1 Introduction 1343 91.2 Modular foundations 1344 91.3 Off-site manufactured solutions – the rationale 1344 91.4 Pre-cast concrete systems 1345 91.5 Modular retaining structures 1349 91.6 References 1349 SECTION 9: Construction verifi cation 1351 Section Editor: M. Brown and M. Devriendt Chapter 92: Introduction to Section 9 1353 M. Devriendt and M. Brown Chapter 93: Quality assurance 1355 D. Corke and T. P. Suckling 93.1 Introduction 1355 93.2 Quality management systems 1355 93.3 Geotechnical specifi cations 1355 93.4 Role of the resident engineer 1356 93.5 Self-certifi cation 1356 93.6 Finding non-conformances 1357 93.7 Forensic investigations 1359 93.8 Conclusions 1360 93.9 References 1361 ICE__MGE_Prelims_Vol 2.indd viii ICE__MGE_Prelims_Vol 2.indd viii 1/13/2012 11:16:47 AM 1/13/2012 11:16:47 AM ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com ix Contents – volume II ice | manuals 100.4 Implementation of planned modifi cations during construction 1497 100.5 ‘Best way out’ approach in OM 1499 100.6 Concluding remarks 1500 100.7 References 1500 Chapter 101: Close-out reports 1503 R. Lindsay and M. Kemp 101.1 Introduction 1503 101.2 Reasons for writing close-out reports 1503 101.3 Contents of close-out report 1505 101.4 Reporting on quality issues 1506 101.5 Reporting on health and safety issues 1506 101.6 Documentation systems and preserving data 1507 101.7 Summary 1507 101.8 References 1507 Index to volumes I and II 1509 99.6 Steel and cast iron 1475 99.7 Timber 1477 99.8 Geosynthetics 1478 99.9 The ground 1479 99.10 Aggregates 1481 99.11 Grout 1482 99.12 Drilling muds 1483 99.13 Miscellaneous materials 1484 99.14 Re-use of foundations 1485 99.15 References 1486 Chapter 100: Observational method 1489 D. Patel 100.1 Introduction 1489 100.2 Fundamentals of OM implementation and pros and cons of its use 1491 100.3 OM concepts and design 1492 ICE__MGE_Prelims_Vol 2.indd ix ICE__MGE_Prelims_Vol 2.indd ix 2/10/2012 7:06:30 PM 2/10/2012 7:06:30 PM Section 5: Design of foundations Section editor: Anthony S. O'Brien ICE_MGE_Ch51.indd 729 ICE_MGE_Ch51.indd 729 1/13/2012 10:33:21 AM 1/13/2012 10:33:21 AM ice | manuals ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com 731 doi: 10.1680/moge.57098.0731 Figure 51.1 outlines the layout and contents of Section 5 Design of foundations. Foundation design is usually divided into two broad cat- egories: shallow and deep, and these categories are also used here. In modern foundation engineering it is helpful to con- sider a third category: hybrid. Hybrid foundations have their own unique features, although their design usually requires an assessment of both shallow and deep foundation behaviour. Examples of hybrid foundations include deep ground improve- ment and piled rafts. The fi nal set of topics, special issues, include building on fi lls, the infl uence of global ground movements on deep foundations, and foundations subject to cyclic and dynamic loading, including earthquakes. In common with other sections of this manual, this section is intended to provide guidance to practising engineers. Given the enormous breadth of the subject and the vast range of ground conditions and structures which a foundation designer may encounter, this section cannot, within the available space, be completely comprehensive. The intent is to outline: the f ■ undamental principles of good design practice; the key mechanisms of ground and ground–structure interaction ■ behaviour which need to be considered; Chapter 51 Introduction to Section 5 Anthony S. O’Brien Mott MacDonald, Croydon, UK Figure 51.1 Layout of chapters in Section 5 Design of foundations Related topics Context and fundamental ground behaviour Sections 1, 2 and 3 Related topics Site investigation Section 4 Construction processes and verification Sections 8 and 9 Foundation types and conceptual design principles Selecting the appropriate foundation type Chapter 52 Shallow foundations Chapter 53 Deep foundations Special issues Hybrid foundations Global ground movements and effects on piles Chapter 57 Building on fills Chapter 58 Pile groups Single piles Chapter 54 Chapter 55 Rafts and piled rafts Chapter 56 Chapter 59 Design principles for ground improvement Rafts Strip and pad footings Chapter 60 Foundations subject to cyclic and dynamic loads ICE_MGE_Ch51.indd 731 ICE_MGE_Ch51.indd 731 2/10/2012 6:23:10 PM 2/10/2012 6:23:10 PM Design of foundations 732 www.icemanuals.com ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers commonly used design methods; ■ the need to integrate a range of specialist disciplines at different ■ stages of the design process; and to provide: references for detailed study; ■ some brief case histories which highlight key issues. ■ A quote from Terzaghi (1936) is particularly pertinent: Whoever expects from soil mechanics a set of simple, hard and fast rules for settlement computations will be deeply dis- appointed…The nature of the problem strictly precludes such rules. Hence, it is essential for the foundation designer to think care- fully about the likely deformation and failure mechanisms which may occur both during and after construction; then compile a checklist of questions which need to be considered and answered. There have been enormous developments in founda- tion engineering during the last few decades. Despite these developments, failures still regularly occur and there are also numerous examples of grossly overconservative design and poor construction practice. There are several commercial and technical factors that can cause these problems. Technically, it is important to: (i) Recognise that foundation engineering is a ‘process’, and that success depends on a series of interlinked activities during both design and construction. (ii) Have a coherent approach to ground risk management; the ‘geotechnical triangle’ is a valuable framework in this context. An understanding of the site’s history and its groundwater regime are critically important. (iii) Have good communication across different design/con- struction teams. (iv) Develop a good understanding of ground–structure interac- tion. It is vitally important for geotechnical and structural engineers to have early two-way discussions, so that the overall behaviour of the proposed works are understood. In particular, the best opportunity for economic founda- tion design is to set realistic (rather than arbitrary and usu- ally overconservative) limits on foundation movement. (v) Have a good awareness of relevant case histories of past foundation performance, and to carefully assess the rel- evant parameters for assessing stability – and in particu- lar, foundation deformation. Sophisticated analysis is not a substitute for a proper selection of design parameters, based on well designed and supervised ground investigations. Chapter 9 Foundation design decisions provides an introduc- tion to these themes, and these are developed in more detail throughout Section 5. Although it is a simplifi cation, it is fair to state that routine ground investigation and analysis methods can lead to: (i) overconservative design of foundations in heavily over- consolidated soils, such as stiff clays; (ii) unsafe foundation design in normally and lightly overcon- solidated soils, such as soft clays. Modern developments in ground investigation and geotechni- cal analysis can avoid these problems, although these modern techniques are still under-used across the civil engineering industry. The chapters in Section 5 highlight some of the devel- opments which are mature enough to be used more routinely. It is hoped that Section 5 will stimulate an improvement in foundation design practice. ICE_MGE_Ch51.indd 732 ICE_MGE_Ch51.indd 732 2/10/2012 6:23:10 PM 2/10/2012 6:23:10 PM ice | manuals ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com 733 doi: 10.1680/moge.57098.0733 CONTENTS 52.1 Introduction 733 52.2 Foundation types 734 52.3 Foundation selection – conceptual design principles 735 52.4 Allowable foundation movement 747 52.5 Design bearing pressures 752 52.6 Parameter selection, introductory comments 754 52.7 Foundation selection – a brief case history 759 52.8 Overall conclusions 763 52.9 References 763 52.1 Introduction This chapter outlines the types of foundation that are com- monly used, together with the key factors which need to be considered before selecting a particular foundation type. Foundation engineering requires a working knowledge of: geotechnical engineering; ■ construction methods; ■ ground-structure interaction. ■ Professor Peck (1962) outlined the three areas of knowledge that are needed in geotechnical engineering: (i) a knowledge of precedents, i.e. a knowledge of case histories; (ii) a working knowledge of geology; (iii) familiarity with soil mechanics. In the vast majority of cases, a foundation design is developed on the basis of an appreciation of the site geology, the nature of the proposed structure and any particular site constraints. The role of analysis is then to check that a proposed foundation design will be acceptable. Although analysis is important it is just one part of the overall design process. Many young civil engineers will have some knowledge of (iii), but it is important that they endeavour to develop their knowledge of (i) and (ii) above. A knowledge of geology (and hydrogeology) is critically important, since it enables many of the risks associated with foundation engineering at a particular site to be assessed. Simplifying assumptions have to be made before any analysis can be carried out (this includes sophisti- cated computer modelling). The site geology and hydrogeol- ogy have to be considered and understood, as early as possible in the project. Discussions should be held with an experienced geologist. Relevant technical literature and, particularly, local case histories should be reviewed. Once this has been done then the appropriateness, or not, of certain assumptions inher- ent in a particular method of calculation can be judged, and the likely errors associated with the predictions from calculations can be assessed. A knowledge of case histories is probably the most important of the three attributes, since this enables the engineer to have an understanding of: (i) what has worked, or not, in the past; (ii) the consequences of particular construction activities on subsequent performance; (iii) past performance, against which the reliability of differ- ent methods of analysis can be compared; (iv) when a proposed activity is going beyond what has been attempted before – this will then require a special effort and expert advice in order to safely develop the design. A foundation is a structural member and supports a superstruc- ture. So an awareness of the sources and nature of structural loads, the structure’s tolerance of foundation movements, and an understanding of ground–structure interaction is also needed. Finally, the foundations must be built economically and safely. Hence, a designer needs to have an appreciation of construc- tion methods and equipment, in order to develop a design that is practical to build. This list of attributes, which a foundation designer needs to possess, is rather intimidating. The author has not yet come across the god-like creature who possesses a perfect knowledge of all these topics. Therefore, fi rst and foremost, the foundation designer must be prepared to ask questions and discuss these with other design and construction specialists (e.g. geologists, structural and material engineers, specialist sub-contractors, etc.). Good foundation design is usually the result of a multi- disciplinary team effort, where two-way communications across the team occur regularly and frequently. Chapter 52 Foundation types and conceptual design principles Anthony S. O’Brien Mott MacDonald, Croydon, UK The main types of foundation include: shallow foundations (pad, strip, raft); deep foundations (piles, caissons, barettes) and hybrid foundations (deep ground improvement, piled rafts). Foundation engineering requires a broad range of skills, from an appreciation of geology and hydrogeology to structural engineering. The performance of foundations is dependent not only on how they are designed, but also on how they are constructed. The overall design process needs to be well managed, to ensure that there are good communications between different design teams and between design and construction. To provide a framework for selecting the most appropriate type of foundation, a useful mnemonic is ‘the 5 S’s’: S – Soil; S – Structure; S – Site; S – Safety; S – Sustainability The magnitude of allowable foundation movement is a key factor in determining the type, size and cost of foundations, and this chapter provides guidance on routine limits. Parameter selection is a common pitfall, and the critical information requirements are described. ICE_MGE_Ch52.indd 733 ICE_MGE_Ch52.indd 733 2/10/2012 6:28:22 PM 2/10/2012 6:28:22 PM Design of foundations 734 www.icemanuals.com ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers 52.2 Foundation types There are two generic types of foundation: shallow and deep. Foundations developed on improved ground can be considered to be a hybrid of both shallow and deep foundations, although ground improvement design requires additional considerations. The advantages and disadvantages of different foundation types are outlined in Table 52.1. (1) Shallow foundations: these typically comprise pad, strip or raft foundations; refer to Figure 52.1. Pad foundations, Figure 52.1(a), may be square, circular or rectangular. A pad foundation usually only supports one or two col- umns. Strip foundations (Figure 52.1(b)) are commonly used to provide support to a load-bearing wall or for sev- eral closely spaced columns. The length of a strip foun- dation is much greater than its width. A raft foundation (Figure 52.1(c)) could support the entire structure or a substantial part of it. A ‘compensated’ raft (also known as a ‘buoyant’ raft) is a special type of raft. It includes a void, thereby reducing the ‘net’ increase in bearing pressure (section 52.5) on the ground below the foundation. This will increase the factor of safety against bearing capacity failure and reduce foundation settlement, compared with a conventional raft. The structural form of shallow founda- tions can vary, but pad and strip foundations could com- prise either mass concrete or reinforced concrete, whereas raft foundations usually comprise reinforced concrete. The soil resistance to the loads applied by the structure are predominantly developed by the near-surface soil below the base of the foundation. Shallow foundations are usu- ally constructed using simple excavation plant and general labour. Tomlinson et al. (1987) gives useful advice on rou- tine foundation design for low-rise buildings. (2) Deep foundations: for the majority of routine structures, deep foundations comprise piles; refer to Figure 52.2. There are numerous different types of pile, discussed in Chapter 54 Single piles although piles are usually classifi ed as either driven or bored. Pile construction is a specialist activity and should only be carried out by contractors who have the appropriate equipment and experience. The layout of pile foundations can vary substantially from a single pile below a load-bearing column, to a large number of piles in a group supporting the entire structure, via a pile cap (which transfers load from the structure directly into the piles). For a conventionally designed pile group, it is assumed that the piles carry the entire load. Deep foundations also include barettes, shafts or cais- sons, which tend to be bespoke foundations for special circumstances. Caissons, barettes and shafts typically have a large diameter or cross-sectional area relative to their depth in comparison with conventional piles. Barettes are rectangular in plan, and are installed using diaphragm-wall construction techniques. Both shafts and caissons are circular in plan; however, they are usually constructed by different methods. Shafts could be hand- dug or excavated using back-actors, with excavation sup- port installed top-down, using pre-cast concrete rings or cast-in situ concrete lining. Caissons are usually jacked or sunk into place using combinations of kentledge, excava- tion and perimeter lubrication (using bentonite). For both piled foundations and deep shafts the load transfer to the ground is via shear along the vertical sides of the shaft or pile and by end-bearing resistance. Piled rafts are a hybrid type of foundation with the struc- tural load being transferred to the soil via the raft (as for a shallow foundation) and the piles (as for a deep foundation). The principal difference between a piled raft and a conven- tional pile group is that the piles are designed to mobilise most of their ultimate load-bearing resistance and act as settlement-reducing elements whilst the raft provides the appropriate overall factor of safety against bearing capacity failure. Compared with a conventional pile group, a piled raft has a relatively small number of widely spaced piles (Figure 52.3). Piled-raft design requires specialist input. (3) Foundations on improved ground: in general, the pur- pose of ground improvement is to increase the strength and stiffness of the ground below a proposed structure, and then shallow structural foundations are constructed on the surface of the improved ground (Figure 52.4). Below the structural foundations, a granular layer (some- times reinforced with geogrids) is often used to transfer loads into the reinforcing elements (Figure 52.4). The mechanism of ground improvement is usually either: (i) Mass reinforcement – usually for clays, silts or made ground. A large number of stiff elements are intro- duced into the compressible layer. (ii) Densifi cation – usually for sands or gravels. A com- paction process forces a rearrangement of the soil particles into a denser state. Reinforcement: techniques such as vibro stone columns or deep soil mixing facilitate the replacement of soft com- pressible materials by stronger materials introduced into the ground via specialist equipment. These stronger elements carry most of the foundation load. However, the remaining soft compressible materials will also carry some of the foun- dation loads, hence the term ‘reinforcement’. It is important to note that the reinforcing elements usually have negligible tensile and bending resistance. Sometimes reinforcing ele- ments such as stone columns are called ‘stone piles’; how- ever, this is quite incorrect and misleading. Foundations built upon improved ground will behave in a quite different manner to piled foundations (Figure 52.5). Densifi cation: soils such as loose sand with a low silt or clay content can be compacted into a denser state. Once den- sifi ed the sand will be a more competent stratum and be able to carry the foundation loads directly. Hence, conventional shallow foundations can be placed on the densifi ed layer. ICE_MGE_Ch52.indd 734 ICE_MGE_Ch52.indd 734 2/10/2012 6:28:22 PM 2/10/2012 6:28:22 PM Foundation types and conceptual design principles ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers www.icemanuals.com 735 Densifi cation may be carried out via a wide range of spe- cialist equipment. The key issue for densifi cation projects is usually the relative density that can be achieved compared with the value which is needed to ensure that foundation settlement is acceptable. The success of ground improvement (both by reinforce- ment or densifi cation) is sensitive to the nature of the soil profi le and the soil macrofabric. For example, densifi cation by vibrocompaction may be straightforward if the sand is homogeneous and has a low silt or clay content. Compaction will be much more diffi cult and often less effective if there are numerous bands of silt or clay in the sand. These soil features can be easily missed by conventional boreholes and sampling at discrete depth intervals. Continuous sampling or profi ling techniques (such as static cone penetration testing, CPTs) are usually very benefi cial when designing ground improvement. Similar considerations can apply to reinforce- ment techniques. Quality control and fi eld testing in order to verify the effectiveness of ground improvement are a signifi - cant component of any ground-improvement project. 52.3 Foundation selection – conceptual design principles 52.3.1 Information requirements and the foundation design process Figure 52.6 outlines the typical information requirements, the design deliverables (reports, etc.) and the project phases that are followed to design and construct a foundation. During the early stages the key questions are: (1) Site geology, hydrogeology and history: what are the geo- logical age and the depositional environment of the main deposits under the site? What subsequent changes may have occurred (e.g. landslides, man’s infl uence)? (2) What will be built?: form of structure, likely construction methods, main site constraints, applied loads, principal constraints (e.g. allowable structural movements)? (3) Engineering knowledge: what existing knowledge do we have? For example, relevant technical literature, good case histories, local customs and experience or expertise. This collation of available data into a desk study report is an important and cost-effective means of managing ground risks on a project. Sole reliance on boreholes in the absence of a proper desk study is potentially very dangerous. The main ground hazards can be identifi ed from the desk study and the key fea- tures of ground behaviour can be assessed. This will inform the design of intrusive ground investigation (refer to Chapters 40 The ground as a hazard, 41 Man-made hazards and obstructions, 43 Preliminary studies and 44 Planning, procurement and manage- ment). It is often the case that designers ‘inherit’ ground inves- tigation reports from previous or adjacent projects and studies. It is very important that the scope, adequacy and reliability of this information are assessed in the context of the current project requirements. If the structure has been relocated, or more oner- ous loading or allowable movement criteria are required, then an additional ground investigation may be needed (perhaps using more sophisticated investigation techniques). Foundation design is an iterative process. Once relevant information has been obtained for the site, the key data should Superstructure column Bearing wall (or multiple colomns) Ground surface Ground surface (a) (b) (c) (d) Pad Strip Raft ‘Compensated’ raft Entire structure Entire structure Void B L B B T D D T Figure 52.1 Types of shallow foundations ICE_MGE_Ch52.indd 735 ICE_MGE_Ch52.indd 735 2/10/2012 6:28:22 PM 2/10/2012 6:28:22 PM Design of foundations 736 www.icemanuals.com ICE Manual of Geotechnical Engineering © 2012 Institution of Civil Engineers Figure 52.2 Deep foundation, conventional pile group Figure 52.3 Hybrid foundation, piled raft Original soil (uncompacted) Shallow foundation, raft or strip foundations Ground mass, densified Ground mass, densified beneath foundations beneath foundations Ground mass, densified beneath foundations Ground mass, Ground mass, reinforced beneath reinforced beneath foundations foundations Ground mass, reinforced beneath foundations Most of foundation load taken by reinforcing elements Lateral confinement by natural ground (?) (a) Ground improvement by densification (b) Ground improvement by reinforcement Some foundation load resisted by natural ground Ground surface Ground surface Geogrid reinforced granular layer (?) Pad/strip foundations Competent soil layer Competent soil layer Figure 52.4 Hybrid foundation – deep ground improvement be summarised on a plan and vertical cross-sections through and beyond the site boundaries. Drawn to scale, with levels referenced to an appropriate survey datum, as a minimum, the following features should be drawn: (i) the previous and proposed ground surfaces; (ii) any previous and neighbouring structures and under- ground services; (iii) ground profi le, strata boundaries (including selected ground properties from testing); (iv) groundwater levels; (v) outline of the proposed structure and proposed locations for foundations; (vi) list as bullet points, the key site constraints and hazards. Based on a knowledge of the ground profi le, the type of struc- ture and key site constraints, an experienced engineer should be able to identify appropriate conceptual designs for the foun- dations. Analyses would then be carried out to check that this concept had an acceptable level of stability and that foundation movements were acceptable. If these are not acceptable, then the concept would be modifi ed (say, pile foundations would ICE_MGE_Ch52.indd 736 ICE_MGE_Ch52.indd 736 2/10/2012 6:28:23 PM 2/10/2012 6:28:23 PM

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