A Guide to Field Instrumentation in Geotechnics: Principles, Installation and Reading

232 Pages·2011·59.077 MB·English

by  Richard Bassett

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Geotechnical instrumentation is used worldwide, particularly in urban areas, for recording the n

physical responses of soils and structures to natural phenomena and new civil engineering works. i
n
It enables engineers to assess the performance and impact of many sizable projects. The output

is also used for recording and controlling remedial works and for assessing safety. G
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This book provides easily accessible guidance on a broad range of instrumentation, dealing with
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the conceptual philosophy behind the use of instruments, and presenting systematic coverage of e
their practical use. It discusses the use of displacement-dominated systems and load- or stress- c
h
based systems, and outlines their limitations and their relative advantages and disadvantages. A Guide to Field
n
The relevant theoretical soil mechanics background is presented in some detail and provides
i
c
a simplified model against which the data can be assessed. The book also includes the basic
s
concepts behind advanced electronic techniques, such as laser scanning in surveying and fibre-
optics, with up-to-date coverage of the rapidly changing communication and data recovery
systems. Instrumentation
It is written for senior designers, consulting engineers and major contractors who need a R
comprehensive introduction to the general purpose, availability and analysis of field instruments ic
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before details of their own project can be progressed. It also serves as a textbook for any specialist a
r
geotechnical MSc or professional seminar courses in which instrumentation forms a major part. d in Geotechnics

B
Richard Bassett is former head of Geotechnics at University College, London. He has extensive a
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industry experience as lead consultant to the itmsoil group. s
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GeoTeCHnICaL enGIneerInG Principles, installation and reading
Cover image: © Savvy & Victor
www.sponpress.com Richard Bassett
A Guide to Field Instrumentation
in Geotechnics
Geotechnical instrumentation is used worldwide, particularly in urban areas, for
recordingthephysicalresponsesofsoilsandstructurestonaturalphenomenaandnew
civilengineeringworks.Itenablesengineerstoassesstheperformanceandimpactof
manysizableprojects.Theoutputisalsousedforrecordingandcontrollingremedial
worksandforassessingsafety.
Thisbookprovideseasilyaccessibleguidanceonabroadrangeofinstrumentation,
dealingwiththeconceptualphilosophybehindtheuseofinstruments,andpresenting
systematic coverage of their practical use. It discusses the use of displacement-
dominated systems and load- or stress-based systems, and outlines their limitations
andtheirrelativeadvantagesanddisadvantages.Therelevanttheoreticalsoilmechan-
ics background is presented in some detail and provides a simplified model against
which the data can be assessed. The book also includes the basic concepts behind
advanced electronic techniques, such as laser scanning in surveying and fibre-optics,
with up-to-date coverage of the rapidly changing communication and data recovery
systems.
It is written for senior designers, consulting engineers and major contractors who
needacomprehensiveintroductiontothegeneralpurpose,availabilityandanalysisof
field instruments before details of their own project can be progressed. It also serves
as a textbook for any specialist geotechnical MSc or professional seminar courses in
whichinstrumentationformsamajorpart.
RichardBassettisformerheadofGeotechnicsatUniversityCollege,London.Hehas
extensiveindustryexperienceasleadconsultanttotheitmsoilgroup.
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[17:4522/11/20115681-bassett-frontmatter.tex] JobNo:5681 Bassett:AGuidetoFieldInstrumentationinGeotechnics Page:ii 1–xviii
A Guide to Field
Instrumentation in Geotechnics
Principles, installation and reading
Richard Bassett
[17:4522/11/20115681-bassett-frontmatter.tex] JobNo:5681 Bassett:AGuidetoFieldInstrumentationinGeotechnics Page:iii 1–xviii
CRC Press
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Contents
Listoffiguresandtables ix
Foreword xvii
Acknowledgements xviii
Introduction 1
1 Thegeneralphilosophyofgeotechnicalinstrumentation 2
Philosophy 2
Levelsofinstrumentation 3
Ratesofchange 3
Typesofmonitoring 3
2 Basicsoilmechanicsandporepressures 6
Soilsasasimplifiedmodel 6
Porepressuremeasuringinstruments 14
Typesofpiezometer 14
Removablepiezometers 20
Usingthesimplifiedmodeltointerpretporewaterpressure
responses 20
Cuttings 26
Embankments 28
Tunnels 30
3 Displacementsandglobaldeformations 37
General 37
Strainsanddeformations 38
Verticaldisplacementswithinstructuresandsoils 38
Hydraulics 39
Piezometersettlementcells 40
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vi Contents
Displacementofstructures 43
Incorrectuseofelectrolevelbeamsystems 46
Horizontaldisplacementsinstructures 51
Verticaldisplacementsinsoilsbymechanicalmeans 51
Micrometersettlementmeasurements(therod
extensometer) 53
Magneticplatesandreedswitchsensors(themagnetic
extensometer) 55
Deformationsinsoilsusinginclinometersandhydrostatic
profilegauges 57
Inclinometers:thetechnician 60
Inclinationandthereadingunit 61
Theinclinometerbody 62
Minimisinginstrumentzeroandsmallcasingerrors 66
Fundamentalsofinclinometerinstallation 68
Thereferencecasing 69
Theborehole 71
Theinstallation 73
Installationprocedure 74
Theoreticalconceptsbehindboreholegrouting 74
Subsequentsoildisplacement 76
In-placeinclinometers 78
Horizontalprofilegaugesusinganinclinometerprobeor
IPIunits 80
Interpretation 80
Datareduction 82
Advancedusesofcombinedhorizontalandvertical
displacements 88
TheMohrcircleofstrain 89
4 Vibratingwireinstrumentsandlocalisedmeasurementofstrains 100
Basicmechanicsofvibratingwireinstrumentsandlinearstrain
measurement 100
Realdesignconsiderations 101
Loadcellsandembeddedstraingaugesusingthereactionbeam
asthestraincontrol 106
Loadandstresses 109
Analysisofstressestoprovidefullstressanalysis 109
Theinterpretationofvibratingwireinstruments 110
Assessmentandinterpretationofvibratingwiredata 110
Strains 111
Datainterpretation 113
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Contents vii
Porepressurechange 116
Interpretingothervibratingwireinstruments,loadcells
andcrackmeters 117
Cracksanddamagemeasurement 117
Crackmonitoringinstruments 121
5 Surveytechniques 126
Totalstationmonitoring 126
Useofautomatictotalstations 126
Prisms 133
Mountingsystems 137
Limitationsintunnels 137
Advancedopticalsystems 140
6 Specialistinstruments 144
TheBassettconvergencesystem 144
Thegeometricprinciplesofabar/camunit 144
Geometryofthebeam/camsystem 147
TheBCSfieldtrial,systemconfiguration 152
Datacaptureandprocessing 154
Measurements 154
Temperaturechanges 157
Traintransiteffects 157
Theinfluenceoftheexcavationofanewadjacent
tunnel 158
Conclusions 159
Fibre-opticsystems 160
7 Instrumentsystemsfortunnellingprojects 167
Initialassessment(experience) 167
Tunnellingandinstrumentation 168
Preliminarypredictions 168
Numericalassessment 177
Instrumentation 183
Fieldinstrumentationlayouts(ideal) 185
Convergence 185
Structuresanddeformations 187
Globalsettlementatgroundlevel 187
Datapresentation 194
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viii Contents
8 Datalogging,recoveryandpresentation 201
Basics 201
Radioconnection 203
Meshnetworks 205
WiFiandIPaddresssensors 205
Internet-baseddatapresentationandundergroundconstruction
informationmanagementsystems(UCIMS) 206
9 Conclusions 209
Notes 211
References 212
Index 213
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Figures and tables
2.1 Diagramoftheconceptofvoidratio 7
2.2 Idealisedcolumnofsoilexperiencingone-dimensionalconsolidation 7
2.3 Normalconsolidationforaclaysoilona1+e/normalstressplot 8
2.4 Normalconsolidationforaclaysoilona1+e/log normal
e
stressplot 8
2.5 Unloading(swelling)curvesona1+e/normalstressplot 9
2.6 Equilibriumstressesonarectangularelement 10
2.7 ‘Mohrcircleofstress’atfailure 10
2.8 ‘Mohrcircleofstress’foradrainedmaterialwithcementingor
cohesion 11
2.9 Deformationintheprincipalstressdirections 11
2.10 Idealisedgraincontact 13
2.11 Stateboundaryrelationshipsforaclayonanelasticunloadingline 13
2.12 ThesimplifiedellipseformassumedintheRoscoe–Burlandversion
intheCRISPprogram 15
2.13 Setofstateboundarysurfaces 15
2.14 Isometricviewofthestateboundarysurfaceons(cid:2),t,1+eaxes 15
2.15 Simplifiedporepressuremeasuringunit 16
2.16 Flushablemodificationtoapiezometer 16
2.17 Schematicdiagramofapneumaticpiezometer 17
2.18 Deformationofadiaphragm 17
2.19 Arrangementofadiaphragm 18
2.20 SimplifiedfullWheatstonebridgecircuit 18
2.21 Suctiongauge(afterImperialCollege,London) 19
2.22 TheBATpiezometersystem(courtesyProfoundBV) 19
2.23 Undrainedsurface(1+e=constant) 21
2.24 Detailedwallsection 22
2.25 LocationsofinitialtotalstressforAtoE 22
2.26 Magnifiedrotationofthewallduetoexcavation 23
2.27 TotalstresspathsAtoE 23
2.28 StresspathsforelementA 23
2.29 StresspathsforelementsBandC 24
2.30 Changesinporewaterpressure(pwp)/depthofexcavation 25
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