喷射混凝土巷道应力测量仪的性能外文文献翻译中英文翻译.docx

喷射混凝土巷道应力测量仪的性能外文文献翻译中英文翻译.docx

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喷射混凝土巷道应力测量仪的性能外文文献翻译中英文翻译

英文原文

Theperformanceofpressurecellsforsprayedconcretetunnellinings

C.R.I.CLAYTON,J.P.VANDERBERG,G.HEYMANN,A.V.D.BICAandV.S.HOPE

Abstract:

Thepaperexaminesthefactorsthataffecttheperformanceoftangentialcellsembeddedinshotcretetunnellinings.Newdata,derivedfromfieldmonitoring,numericalmodelling,andcalibrationtestscarriedouttosimulatetheembedmentandcrimpingprocesses,arepresented.Thesesuggestthatalthoughwell-designedembeddedtotalpressurecellswillhavecellactionfactorsclosetounity,theycannotbeassumedtoprovidereasonableestimatesofthestresseswithinsprayedconcretelinings,unlesstheinfluencesofinstallationeffects,temperaturechanges,shrinkageandsubsequentcrimpingcanbetakenintoaccount.

Keywords:

fieldinstrumentation;tunnels.

Introduction

Thepressurecellsusedformeasuringthecompressivestressesinshotcretetunnelliningsgenerallyconsistoftwostainlesssteelplateswithathinfluid-filledcavitybetweenthem.Thecavityisconnectedeithertoamembrane-typebypassvalveortoavibrating-wirepressuretransducer.Theuseofotherdirect-stressinstrumentshasbeenreportedintheliterature,althoughinfrequently.Pressurecellsaretypicallyinstalledinoneoftwoorientations:

radial,torecordthestressbetweenthesprayedconcreteandthegroundsurroundingthetunnel;andtangential,torecordthehoopstresswithinthetunnelliningitself.Thispaperconsidersonlytangentialcells.

Despitetheirwidespreaduseinpractice,therehasbeenverylittleresearchreportedintheliteratureontheuseandbehaviourofshotcretepressurecells.Manypractitionersremaindoubtfuloftheabilityofembeddedpressurecellstomeasuretheactualstressesinconcretetunnellinings.Inapreviouspaperreviewinginstrumentationforsprayedconcretelinedtunnelsthepresentauthorsnotedsomeofthepotentialdifficulties,statingthatitwas`extremelyunlikelythatembeddedcellsbeusedformonitoringtheactualstressinatunnellining'.Yet,potentially,pressurecellsareavaluablesourceofinformationthatmightbeusedtoassesswhethertunneldesignassumptionsarejustified,andthispaperthereforereportsthefindingsofourfurtherresearchintothisimportanttopic.

Factorsaffectingthepressuresrecordedbytangentialpressurecellsintunnellinings

Directstressmeasurementwithinanymediumismadedifficultbythemanyfactorsthatcanaffecttheresults.Inthecaseoftangentialpressurecellsembeddedinshotcreteourrecentexperiencesduringtunnelmonitoringsuggestthattheseareasfollows.

Cellproperties

Thecellshouldbeconstructedsothatthestressesintheshotcretearenotsignificantlymodifiedbyitspresence.Sincethecompressibilityofthefluidinthecellislessthanthesurroundingmaterialsitwillunder-read,butthiscanlargelybecompensatedforbymakingthecellwideandthin.Theuseofcellfluidssuchasmercuryoroilwillaffectnotonlythecompressibilityofcellsbutalsotheirtemperaturesensitivity.Changesintemperaturewillexpandthefluidagainstthesurrounding,relativelyrigidcellmetalandsurroundingconcrete,andwillproduceachangeinmeasuredstress.

Installationeffects

Theinadvertentformationofcavitiesaroundthecellduringshotcretingwillleadtoasoftmeasurementsystem,whichwillsubsequentlyunder-read.Incorrectpositioningofthecellwithinthelining,rotatingittowardstheradialdirection,canalsocauseittounder-readsomewhat,becauseradialstressesaretypicallylessthan10%oftangential.Indeedtheactualthicknessoftheliningatthepointofinstallationwillalsoaffecttheinterpretationofthestressmeasurements.

Post-installationfactors

Asnotedabove,temperaturechangescanbeexpectedtoleadtochangesinmeasuredstresses.Shrinkageduringtheearlylifeoftheshotcretewillresultinchangesintherecordedstressthatarenotduetoexternalstresschanges.Crimping,whichisoftenundertakentoensurethatpressurecellsareproperlybeddedwithintheshotcrete,canprovideasignificantoffsettothemeasuredpressures.

Numericalandphysicalexperiments,andresultsfrommonitoring

Numericalmodellingandphysicalsimulationhavebeencarriedouttoassesstheactualperformanceofsomestresscellsusedinpractice,andtoplacetheirperformanceinthecontextofothercelldesigns.

Numericalmodellingtoassesstheeffectsofcellfluid

ToexaminetheeffectofcellfluidoncellperformancetwoidealisedcircularcellsembeddedinablockofconcreteweremodelledunderaxisymmetricconditionsusingthefiniteelementpackageLUSAS.ThegeometryofthecellsandthematerialpropertiesmodelledareshowninFig.1.The160mmdiametercellissomewhatlargerthanmanyofthecellscurrentlyinuse,whereasthe80mmcellissmaller,andwasconsideredbytheauthorstobelikelytohaveanexcessiveT/Dratio.Inthefirstnumericalexperimenttheeffectofthebulkmodulusofthecellfluidwasinvestigated,byapplyingaconstantexternalaxialstressandvaryingthecellcavitypressure.Thebulkmodulusequivalenttoeachcellactionfactorwascalculatedbyintegratingthedisplacementsalongthesurfaceofthecellcavity.Fig.2showstheconsiderableinfluenceofbulkmodulusoncellactionfactor,butitalsoshowsthatwhenreasonablecellgeometriesareusedcellactionfactorsremaintolerablyclosetounitywhenoilissubstitutedformercury.

Fig.1.Geometryofcellsandpropertiesofmaterialsusedduringnumericalmodelling:

（a）idealisedpressurecell;（b）geometrymodelled;（c）materialproperties

Fig.2.Effectofbulkmodulusofcellfluidoncellactionfactor

Physicalsimulation

Calibrationtestswereconductedtoevaluatetheperformanceofthevibrating-wiremercury-filledpressurecells,inthreephases:

（a）Duringthefirstphasethemanufacturer'scalibrationofthepressurecellswascheckedbyconductinganairpressurecalibrationonallthecellsused.Thiswasdoneina1mdiameterchamber,inthelaboratory.

（b）Thesecondphaseoftheexperimentalworkwasconductedtoinvestigatewhethertangentialcellsinstalledunderidealandcontrolledconditionscouldproducereliableresults.Thiswasdonebyinstallingtwopressurecellsinaprecastconcreteslab,constructedinthelaboratory.

（c）Thefinalphaseoftheexperimentalworkwasdesignedtoinvestigatetheperformanceofthetangentialcellsunder'workingconditions',aswellastoinvestigatewaysofinstallingthecellstoimprovetheirperformance.Thiswasdonebyinstallingtangentialpressurecellsinshotcreteslabs,formedinatunnelunderworkingconditions.

Thecellsusedfortheexperimentalworkweremercury-filledvibrating-wirecellssuppliedbyGeokon,andwithafull-scalerangeof20MPa（Fig.3）.Allthepressuremeasurementswerecalculatedusingthetemperaturecorrectionsuppliedbythemanufacturer.

Fig.3.Vibrating-wiremercury-filledconcretestresscell

Thesecondphaseofthecalibrationtestingwascarriedouttoinvestigatetheperformanceofthetangentialpressurecellsunderidealandcontrolledconditions.Forthisexperimenttwocellswereembeddedina25MPaready-mixconcreteslab,1.0mhigh,1.0mwideand0.3mthick.Thetwocellsweretiedtoacageconstructedfromreinforcingbarmeshes,whichwereidenticaltothoseinuseintheHeathrowTerminal4stationtunnels.Theexperimentalset-upisshowninFig.4,exceptthatinthefirstsetofexperimentstwobarecellswereused.Onebarecellandoneprecastcellwereusedinasubsequentexperiment,describedlaterinthispaper.

Fig.4.Layoutofcellsembeddedinconcretepanel

Duringthecuringperiodtheslabtemperatureincreasedtoabout32°C,andafterwardsdecreasedslowlyoverseveraldays.Monitoringwascarriedoutuntilthecelltemperaturesreachedequilibriumwiththelaboratoryenvironment（Fig.5）.

Fig.5.Temperaturesmeasuredaftercastingcellsinready-mixedconcrete

Ateachloadincrementthecellreadingswereobservedtostabiliserapidly:

creepeffectswerenotapparent.Thevalueofcellactionfactorwassubsequentlycalculatedfrompressurecellreadingsandaverageappliedverticalstresses.

Thefinalphaseoftheexperimentalworkconsistedoftheevaluationofthetangentialpressurecellsinstalledunder`workingconditions'.Thiswasdonebyplacingtwopressurecellsineachoftwoslabs,similartotheabovebutconstructedusingshotcreteinatunnelatHeathrowTerminal4.Becausetheresultsoftheexperimentonthecellsinstalledintheconcreteslabshowedthatunderidealconditionsthecellsseemtoperformsatisfactorily,itwasarguedthatfailureunderworkingconditionsmightresultfrominstallationeffects.Amajordifficultywiththeinstallationoftangentialpressurecellsisensuringthatnovoidsareformedin`shadowzones'aroundthecellduringshotcreting.Itwasthereforedecidedtoprecastoneofthecellsineachofthetwoslabsinataperedconcreteblock,designedtopreventtheformationofshadowzones（Fig.6）.

Fig.6.Detailofcellcastinprecastconcrete

Discussion

Theoreticalconsiderationssuggestthatawell-designedembeddedcell,withhighstiffnessandalowaspectratio（T/D）,shouldhaveacellactionfactorclosetounity.Ourexperimentsoncommerciallyavailablecellssupportthisview.Theabilityofacelltomeasuretheappliedpressurecorrectlyisdependentuponadditionalfactors,however.Offsetsduetotemperature,crimpingandshrinkagemustbeproperlytakenintoaccount.Thequalityofcellinstallationmustbeassessed.

Althoughmanufacturersroutinelysupplytemperaturecorrecti