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Propagationcharacteristicsofblast-inducedshockwavesinajointedrockmassY.K.Wua,*,H.Haoa,Y.X.Zhoub&K.ChongbaNanyangTechnologicalUniversity,SingaporebLandsandEstatesOrganisation,MinistryofDefence,Singapore(Received5May1998)Thepropagationcharacteristicsofblast-inducedshockwavesinajointedrockmasshavebeenmonitoredandstudied.Accelerometersweresetuponarocksurfacealongthreelines,at08,458and908withrespecttotheorientationofthepredominantjointstrikes.Cylindricalchargesweredetonatedinachargehole,andgroundaccelerationsinbothverticalandradialdirectionsatvariouspointsontherocksurfacewererecorded.Resultsshowthatrockjointshavesignificanteffectsonthepropagationcharacteristicsofblast-inducedshockwaves.Theamplitudeandprincipalfrequencyofshockwavesattenuatewiththeincreaseofdistancefromthechargecentre,andtheincreaseofincidentanglebetweenthejointstrikeandthewavepropagationpath.Themeasureddatawerecomparedwiththeempiricalequationsofshockwaveattenuationproposedbyotherauthors.Themechanismofrockjointeffect,theattenuationofshockwavesinrelationtothepropagationdistance,thechargeweightandtheincidentangle,arediscussedinthispaper.q1998ElsevierScienceLtd.AllrightsreservedKeywords:incidentangle,shockwaves,principalfrequency.1INTRODUCTIONDrillingandblastingarethemostwidelyadoptedexcava-tiontechniquesforundergroundminingandcivilengineer-ing.Rockblastingresultsingroundshockandvibrationwhichmaycausedamagetothesurroundingstructuressuchasbuildings,bridges,damsandtunnels,etc.,therefore,blast-inducedgroundshocksandtheirpropagationinrockmasshavebeendrawingmoreandmoreattention.1Theresearchisparticularlysignificantforundergroundblastsinurbanareas,inordertoreducetheinducedvibrationtoanacceptablelevel.Rockmassisusuallybrokenupbyjointsintorockele-ments,whicharecontinuousandmayberegardedaselasticbodies.Thepropertiesofrockmassaredeterminedbythepropertiesoftherockelementsandthejoints,aswellasbythegeometryofthesystem.Thetermjointcoversalldis-continuitiessuchasjoints,faults,beddingplanesorothersurfacesofweakness.Theexistenceofrockjointsnotonlysignificantlyaffectsthepropertiesofrockmass,butalsotheirseismicresponse,whichiscloselyconnectedtoproblemsingeophysics,earthquakeengineering,miningengineering,petroleumengineering,hydrogeologyandwastedisposal.2Manyeffortshavebeenmadetostudytheeffectsofrockjointsonwavepropagationtheoreticallyandexperimentally.Forinstance,BlairandSpathis3measuredtheattenuationofexplosion-generatedpulseinrockmass.King4measuredtheamplitudesandtraveltimesofhigh-frequencyseismicwavespropagatedparallelandperpendiculartocolumnarjointsinbasalt,andnotedlowerparticlevelocitiesandgreaterhigh-frequencyattenuationinthedirectionperpen-diculartothejointsthaninthedirectionparalleltothem.RobertandStump5studiedtheeffectofgeologicalinhomo-geneityonnear-fieldgroundmotion.Theirobservationsug-gestedthatscatteringbygeologicalinhomogeneityisresponsibleforthefrequency-dependentspatialvariabilityingroundmotion.YuandTelford6investigatedtheeffectofjointwidthandwavefrequency,andconcludedthatwavepropagationacrossjointsisfrequencydependent.Effortshavealsobeenspentontheoreticalstudyofjointeffectsonwavepropagationinrockmass.Therearetwoapproachesinthetheoreticalstudy.Oneistoexaminetheeffectsofasinglejoint,7,8andtheotheristoinvestigatethecomprehensiveeffectsofjointsbyusingequivalentmaterialproperties.9TheapplicationofthesetwoapproachesisSoilDynamicsandEarthquakeEngineering17(1998)407–412q1998ElsevierScienceLtd.AllrightsreservedPrintedinGreatBritain0267-7261/98/$-seefrontmatterPII:S0267-7261(98)00030-X407*Correspondingauthordependentonthesizeofjointsincomparisonwiththewavelength.10Thefirstmethodisusuallyadoptedtoasinglejointcharacterisedbyalargesize,whereasthesecondisusedwhenfracturesaredenseandsmallinsizecomparedwiththeshockwavelength.Incomparisonwiththeeffectsofrockjointsonthemechanicalpropertiesofrockmass,however,lessatten-tionhasbeenpaidtotheireffectsonwavepropagation.2Therearefewerreportsonfieldteststudyofrockjointeffectonshockwavepropagation.Inthepresentstudy,blast-inducedgroundmotionswererecordedonarocksurfaceatdifferentdistancesfromtheexplosioncentre,andindifferentorientationswithrespecttothepredomi-nantstrikeofjoints.Inthispaper,theresultsoffieldmeasurementarepresentedandanalysed,andthemechan-ismofrockjointeffectsonwavepropagationarediscussed.2MEASUREMENTCONFIGURATIONANDINSTRUMENTATIONThefieldlayout,asshowninFig.1,consistsofachargeboreholeof11mindepthandsevenmeasuringpointsontherocksurface.Themeasuringpoints,labelledRS1–RS5,weresetupalongameasuringlinewhichisparalleltothepredominantjointstrike,toexamineshockwavepropaga-tionandattenuationinrockmass.Themeasuringpointsare2.5,5,10,25and50mfromthechargeborehole,withthecorrespondingabsolutedistancesof8.8,9.8,13.1,26.4and50.7mfromtheexplosioncentre,respectively.Toexaminetheorientationeffectsofrockjoints,twoextrameasuringpoints,labelledRS6andRS7,werearrangedsurroundingtheexplosioncentreatadistanceof50m.Theyare458and908withrespecttothestrikeofpredominantjointsets,respectively.Ateachpoint,twopiecesofENDEVCOpiezoelectricaccelerometerswere
本文标题:Propagation-characteristics-of-blast-induced-shock
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