Pressuremeters in Geotechnical Design

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1 Pressuremeters in Geotechnical Design B.G. CLARKE Department of Civil Engineering University of Newcastle upon Tyne BLACK1E ACADEMIC & PROFESSIONAL An Imprint of Chapman & Hall London Glasgow Weinheim New York - Tokyo Melbourne Madras

2 Contents List of symbols xi 1 Introduction Introduction Definition of a pressuremeter The development of the pressuremeter The pressuremeter test The probe The expansion curve Summary 16 2 Pressuremeter probes and testing equipment Introduction Key features of pressuremeters The probe The control unit Prebored pressuremeters The Menard pressuremeter The Oyometer The high-pressure dilatometer Other prebored pressuremeters Self-boring pressuremeters The pressiometre autoforeur The Cambridge self-boring pressuremeter The weak rock self-boring pressuremeter Other self-boring pressuremeters Pushed-in pressuremeters Full displacement or cone pressuremeter The Stressprobe Summary 62 3 Site operations Introduction Installation techniques Introduction Prebored pressuremeters The self-boring pressuremeter The pushed-in pressuremeter Calibrations Introduction Pressure gauges Displacement transducers Total pressure transducers Effective pressure and pore pressure transducers Membrane stiffness Membrane thinning Membrane compression 95

3 Vlll CONTENTS System compression The initial dimension of the probe and readings of the transducers Frequency and relevance of calibrations On-site system checks The test Introduction The Menard method Stress-controlled tests Strain-controlled tests Additional test procedures Testing in ice Summary of test procedures Termination of a test Introduction Maximum pressure capacity Maximum oil capacity Burst membranes Maximum displacement Reduction of data and initial plots Introduction The Menard pressuremeter test and other volume type pressuremeter tests Radial displacement type PBP tests Radial displacement type SBP and PIP pressuremeter tests Summary Analysis of expanding cavities Introduction Distribution of stress and strain Elastic ground Undrained expansion of cylindrical cavity (quick tests in clay) General analysis Linear elastic perfectly plastic soil Non-linear material Drained expansion of a cylindrical cavity (tests in sand) Volume changes General analysis Very dense sands Tests in rock Specific analyses Non-linear stiffness Undrained analysis assuming entire expansion at the limit pressure Coefficient of consolidation Summary 160 Factors affecting the interpretation of pressuremeter tests Introduction Reasons for the use of semi-empirical methods Introduction Effects of installation Effects of the in-situ stress Effects of discontinuities and bands of hard and soft layers Effects of test procedure Effects of test cavity shape Effects of probe type Summary 174

4 CONTENTS 6 Interpretation of pressuremeter tests Introduction Data quality and ground type Introduction Quality of installation Ground type Interpretation of an MPM test: The pressuremeter modulus and modified limit pressure Estimating horizontal stress from a pressuremeter test Introduction Lift-off method Methods based on shear strength Methods based on test procedure Curve fitting methods Correlations The subjectivity of the selection of horizontal stress Modulus Initial modulus Unload/reload modulus Non-linear stiffness profile Undrained shear strength General analysis Elastic perfectly plastic soil Angles of shearing resistance and dilation Limit pressure Consolidation and creep Overconsolidation ratio Summary Design rules and applications Introduction The direct method: the Menard method Shallow foundations The Menard method based on results of SBP tests Axially loaded piles Horizontally loaded piles Ground anchors Other direct design methods for horizontally loaded piles Comparisons between results of pressuremeter and other tests Total horizontal stress Modulus Undrained shear strength Angle of shearing resistance Limit pressure Applications Summary Choice of pressuremeter, specifications and developments Introduction Current state of pressuremeter testing Choosing a pressuremeter A typical specification Costs Future developments 311 Appendix Specifications and quantities 314 A.I Introduction 314 IX

5 X CONTENTS A.2 General 314 A.2.1 The equipment 314 A.2.2 The operator 315 A.3 Probes 315 A.3.1 General 315 A.3.2 Volume displacement type probes 315 A.3.3 Radial displacement type probes 316 A.4 Calibrations 317 A.4.1 Types 317 A.4.2 Total pressure transducer 317 A.4.3 Displacement transducer 318 A.4.4 Pore pressure transducers (if fitted) 318 A.4.5 System compression 318 A.4.6 Membrane stiffness 319 A.4.7 Membrane compression 319 A.4.8 Frequency 320 A.5 Installation 320 A.5.1 Prebored pressuremeters 320 A.5.2 Self-bored pressuremeter 321 A.5.3 Pushed-in pressuremeters 322 A.6 Testing procedure 322 A.6.1 Strain-controlled tests 323 A.6.2 Stress-controlled tests 323 A.6.3 Stress-controlled tests: Menard method 324 A.7 On-site data processing 324 A.7.1 Volume displacement type probes 324 A.7.2 Radial displacement type probes 324 A.8 Interpretation 324 A.9 Information to be submitted 325 A.9.1 Prior to commencing work on site 325 A.9.2 Preliminary results for each test 325 A.9.3 Report data processing and analysis 326 A.9.4 Information to be submitted in the report 326 A.10 Bill of quantities 327 References and bibliography 330 Index 357

DEVELOPMENT OF A ROBUST PUSH-IN PRESSUREMETER

DEVELOPMENT OF A ROBUST PUSH-IN PRESSUREMETER Roger Failmezger, P.E. In-Situ Soil Testing, L.C., Lancaster, Virginia, USA ABSTRACT A push-in pressuremeter was developed using slotted steel casing with