Pressuremeters in Geotechnical Design Pressuremeters in Geotechnical Design B.G. CLARKE Department of Civil Engineering University of Newcastle upon Tyne Taylor &Francis LONDON AND NEW YORK Published by Taylor & Francis 2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN 270 Madison Ave, New York NY 10016 First edition 1995 Transferred to Digital Printing 2007 @ 1995 Taylor & Francis Typeset in 10/12 pt Times by AFS Image Setters Ltd, Glasgow ISBN 0 7514 0041 6 Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences issued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the Glasgow address printed on this page. The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made. A catalogue record for this book is available from the British Library Library of Congress Catalog Card Number: 94-71805 Publisher's Note The publisher has gone to great lengths to ensure the quality of this reprint but points out that some imperfections in the original may be apparent In the 1950s, independent developments of pressuremeters took place in France and Japan which led to the successful use of these probes in ground investigation for foundation design. Design rules were developed from obser- vations of full scale structures which are continually being updated and expanded as greater use is made of pressuremeters. In the 1970s, self-boring pressuremeters were developed in France and the UK to determine ground properties directly, especially in-situ stress, stiffness and strength. This led to significant developments in the analysis and interpretation of pressuremeter tests. The third major technological advance took place in the 1980s with the development of the cone pressuremeter. The principal attraction of the pressuremeter test is that it most closely models an ideal condition in which the ground is positively loaded from the in-situ stress conditions. By observing the deformation with applied pressure, the in-situ stress-strain response of the ground can be obtained. The par- ameters obtained from a pressuremeter test, which include in-situ stress, stiffness and strength, are a function of the probe, the method of installation and the method of testing, as well as the chosen method of analysis and interpretation. The aim of this book is to explain how pressuremeters can be used in geotechnical design. A form of pressuremeter can be used in all ground conditions, from soft clays to hard rocks. The parameters obtained, either directly, theoretically or empirically, represent realistic estimates of ground properties. Detailed descriptions are given of the major developments in pressuremeter technology, highlighting the most common and significant probes. Site operations, including calibrations, installation, testing and data reduction, are described, highlighting national standards. Attention is drawn to the need for careful installation and correct calibrations if the results are to be of value. A brief summary of the theories of cavity expansion, as they apply to pressuremeter tests, is given in order to describe the development and the limitations of the theoretical or empirical methods of interpretation. Design rules and examples of the use of interpreted values of horizontal stress, stiffness and strength are described to show that foundation behaviour can be predicted. This book could not have been written without the considerable efforts of all those involved in pressuremeter testing. I would like to make special mention of a number of people who have had a significant input into my interest in pressuremeter testing. The late Professor Wroth, who pioneered vi PREFACE much of the development in the 1970s and 1980s in the UK, was a source of inspiration and encouragement. His vision led to the formation of research teams at both Cambridge and Oxford, and their work on pressuremeters is continuing throughout the world. M. Gambin and his colleagues of the International Committee on Pressuremeters gave much debate to the inter- national role of pressuremeter testing for design. The recent use of the pressuremeter in the UK could not have taken place without the enthusiasm of J.C.P. Dalton and his colleagues at Cambridge Insitu and the encourage- ment of J. Scarrow and his colleagues at Soil Mechanics Ltd. Finally I would like to thank N. Sugawara, Dr P. Allan and S. Tindale for their help and encouragement. B.G. Clarke Contents List of symbols 1 Introduction 1.1 Introduction 1.2 Definition of a pressuremeter 1.3 The development of the pressuremeter 1.4 The pressuremeter test 1.4.1 The probe 1.4.2 The expansion curve 1.5 Summary 2 Pressuremeter probes and testing equipment 2.1 Introduction 2.2 Key features of pressuremeters 2.2.1 The probe 2.2.2 The control unit 2.3 Prebored pressuremeters 2.3.1 The Menard pressuremeter 2.3.2 The Oyometer 2.3.3 The high-pressure dilatometer 2.3.4 Other prebored pressuremeters 2.4 Self-boring pressuremeters 2.4.1 The pressiomitre alctoforeur 2.4.2 The Cambridge self-boring pressuremeter 2.4.3 The weak rock self-boring pressuremeter 2.4.4 Other self-boring pressuremeters 2.5 Pushed-in pressuremeters 2.5.1 Full displacement or cone pressuremeter 2.5.2 The Stressprobe 2.6 Summary 3 Site operations 3.1 Introduction 3.2 Installation techniques 3.2.1 Introduction 3.2.2 Prebored pressuremeters 3.2.3 The self-boring pressuremeter 3.2.4 The pushed-in pressuremeter 3.3 Calibrations 3.3.1 Introduction 3.3.2 Pressure gauges 3.3.3 Displacement transducers 3.3.4 Total pressure transducers 3.3.5 Effective pressure and pore pressure transducers 3.3.6 Membrane stiffness 3.3.7 Membrane thinning 3.3.8 Membrane compression .. . Vlll CONTENTS 3.3.9 System compression 3.3.10 The initial dimension of the probe and readings of the transducers 3.3.1 1 Frequency and relevance of calibrations 3.4 On-site system checks 3.5 The test 3.5.1 Introduction 3.5.2 The Menard method 3.5.3 Stress-controlled tests 3.5.4 Strain-controlled tests 3.5.5 Additional test procedures 3.5.6 Testing in ice 3.5.7 Summary of test procedures 3.6 Termination of a test 3.6.1 Introduction 3.6.2 Maximum pressure capacity 3.6.3 Maximum oil capacity 3.6.4 Burst membranes 3.6.5 Maximum displacement 3.7 Reduction of data and initial plots 3.7.1 Introduction 3.7.2 The Menard pressuremeter test and other volume type pressuremeter tests 3.7.3 Radial displacement type PBP tests 3.7.4 Radial displacement type SBP and PIP pressuremeter tests 3.8 Summary 4 Analysis of expanding cavities 4.1 Introduction 4.2 Distribution of stress and strain 4.3 Elastic ground 4.4 Undrained expansion of cylindrical cavity (quick tests in clay) 4.4.1 General analysis 4.4.2 Linear elastic perfectly plastic soil 4.4.3 Non-linear material 4.5 Drained expansion of a cylindrical cavity (tests in sand) 4.5.1 Volume changes 4.5.2 General analysis 4.5.3 Very dense sands 4.6 Tests in rock 4.7 Specific analyses 4.7.1 Non-linear stiffness 4.7.2 Undrained analysis assuming entire expansion at the limit pressure 4.7.3 Coefficient of consolidation 4.8 Summary 5 Factors affecting the interpretation of pressuremeter tests 5.1 Introduction 5.2 Reasons for the use of semi-empirical methods 5.2.1 Introduction 5.2.2 Effects of installation 5.2.3 Effects of the in-situ stress 5.2.4 Effects of discontinuities and bands of hard and soft layers 5.2.5 Effects of test procedure 5.2.6 Effects of test cavity shape 5.2.7 Effects of probe type 5.3 Summary CONTENTS 6 Interpretation of pressuremeter tests 6.1 Introduction 6.2 Data quality and ground type 6.2.1 Introduction 6.2.2 Quality of installation 6.2.3 Ground type 6.3 Interpretation of an MPM test: The pressuremeter modulus and modified limit pressure 6.4 Estimating horizontal stress from a pressuremeter test 6.4.1 Introduction 6.4.2 Lift-off method 6.4.3 Methods based on shear strength 6.4.4 Methods based on test procedure 6.4.5 Curve fitting methods 6.4.6 Correlations 6.4.7 The subjectivity of the selection of horizontal stress 6.5 Modulus 6.5.1 Initial modulus 6.5.2 Unload/reload modulus 6.5.3 Non-linear stiffness profile 6.6 Undrained shear strength 6.6.1 General analysis 6.6.2 Elastic perfectly plastic soil 6.7 Angles of shearing resistance and dilation 6.8 Limit pressure 6.9 Consolidation and creep 6.10 Overconsolidation ratio 6.11 Summary 7 Design rules and applications 7.1 Introduction 7.2 The direct method: the Menard method 7.2.1 Shallow foundations 7.2.2 The Menard method based on results of SBP tests 7.2.3 Axially loaded piles 7.2.4 Horizontally loaded piles 7.2.5 Ground anchors 7.3 Other direct design methods for horizontally loaded piles 7.4 Comparisons between results of pressuremeter and other tests 7.4.1 Total horizontal stress 7.4.2 Modulus 7.4.3 Undrained shear strength 7.4.4 Angle of shearing resistance 7.4.5 Limit pressure 7.5 Applications 7.6 Summary 8 Choice of pressuremeter, specifications and developments 8.1 Introduction 8.2 Current state of pressuremeter testing 8.3 Choosing a pressuremeter 8.4 A typical specification 8.5 Costs 8.6 Future developments Appendix Specifications and quantities A.l Introduction