Model for energy-based evaluation of blast waves t

Modelforenergy-basedevaluationofblastwavestoassesssafetyofstructuresS.K.MANDAL*{,M.M.SINGH{,N.K.BHAGAT{andS.DASGUPTA{{CentralMiningResearchInstitute,Dhanbad,India{Director,TechnicalEducationofWestBengal,IndiaDemandforsafeandundamagedperipheryrockwallsinminingandcivilconstructionprojectshasencouragedblastingengineerstostudythedetailsofcontrolledblastingparameters.Variousresearchershaveproposedrecommen-dationsforoptimizingblastdesignandsafemagnitudeofvibration.However,theserecommendationsrequireimprovements.Themagnitudeofavibrationcanbecharacterizedbyreflectionofstratacondition,explosivepropertiesandtheblastpatternimplemented.Itisthusproposedthat,inordertodevelopasafeblastpatterntoachieveundamagedperipheryrockwall,thecharacteristicsofwavesignaturesandtheenergytransferredtotherockmediumshouldbeanalysed.Thispaperanalysesthecharacteristicsofvibrationwavesforvariouschargediameters(25to269mm).Tostudythecharacteristicsofwavesignatures,waveanalysissoftwarewasusedtoanalysevariousparametersofwavesignatures,e.g.durationofvibration,magnitudeofpeak,numberofpeaks,acceleration/decelerationofpeak,energytransmittedtotheinsiturockintermsoftotalenergyandenergyofpeakhold.Itwasobservedthatforsmall-diameterchargedholes,thedurationofvibrationwasshortandthemagnitudeofvibrationattenuatedatafasterrate.Useofalongdelaybetweenrowsandajumpedlongdelaybetweenbufferandperipheryrowfurtherdampenedthemagnificationofvibrationamplitudeanddurationofvibrationforeachdelay.Themagnitudeoftransmittedenergy(totalandpeakhold)waslessforsmall-diameterchargedholesandvariedwithlinearchargeconcentrationandvolumeofrockperholetobeblasted.Forlarge-diameterblastholes,vibrationsignatureshadmorepeaksandoflongerduration,indicatingahighmagnitudeofstrainandpoorstrainrate.Consideringthequantumofenergytransmittedbyvariouschargediameters,thispaperdemonstratesthatlarge-diameterchargedholesproduceahighmagnitudeofstrainwithpoorstrainrateandshouldbeavoidedforcontrolledundamagedperimeterblasting.Forpre-splitblastingwithevenasmallquantityofexplosive,themagnitudeoftransmittedenergywasgreaterthanforsmoothblastingandshouldthusbeavoidedwheresmoothblastingcanbeimplemented.*Correspondingauthor.Email:[e-mail]fMining,ReclamationandEnvironmentVol.21,No.2,June2007,111–125InternationalJournalofMining,ReclamationandEnvironmentISSN1748-0930print/ISSN1748-0949online2007Taylor&Francis:10.1080/17480930601119077Keywords:Wavesignatures;Waveenergy;Durationofvibration;Accelerationanddecelerationofpeak;Numberofpeaks1.IntroductionRestrictedleaseholdland,sprawlingdwellingsaroundminingprojectsandever-increasingdemandforpreciseexcavationworkforbothminingandcivilconstructionprojectshaverevealedtheimportanceofundamagedperipheryrockwallsduringexcavation.Inmining,overbreakordamageofinsiturockendangersstructuralsafetyandaffectstheperformanceofconsecutiveblasts.Similarly,incivilconstructionprojects,overbreakordamageincursextracostsintermsofadditionalmuckingandapplicationofextraconcreteand/orsupport,leadingtoextensionsinprojectcompletiontime.Thedrillandblastmethodiscurrentlythemostacceptableexcavationmethodbecauseitisinexpensiveandcompatiblewithsuddenrequiredchangesinprofileorexcavationsequence.Advancementsinthedevelopmentofdrillingtechnologyhaveledtothecreationoffasterlarge-diameterhigh-capacitydrillmachines,theintroductionofvariedexplosiveparametersinexplosivetechnologyandoptimizationofcost-effectiveblastpatterns.Theadvantageofthedrillandblastmethodhasalsopromptedexcavationengineerstoreview,studyanddevelopoptimizedblastpatternsforsafeandundamagedperipheryrockwalls.Theauthorsbelievethatsincethesafemagnitudeofvibrationatonesitecannotbetrueforothersites,andvibrationcharacteristicsandmagnitudesreflectstrataconditionandblastparametersimplementedatthesite,thesameshouldbestudiedtojustifytheeffectivenessofundamagedperipheralrockmass.Consideringblastpatternsfordifferentchargediameters(25–269mm),thispaperanalysesthecharacteristicsofwavesignaturesfordifferentchargediameters.Consideringfullycoupledcharge,wavesignatureshavebeenanalysedintermsofwavelength,attenuationcharacteristics,andamplitudeanddurationofpeakmagnitude.Themagnitudeofacceleration/decelerationofpeakhold,numberofpeaksandenergytransmittedtotherockmediumintermsoftotalenergyandpeakholdenergywereanalysedusingsoftware.Acomparativestudyofwavesignatureparameterswasusedtoevaluatedifferencesinthecharacteristicsofvibrationsignaturesbetweenpre-splitandsmoothblasting,andtoassesstheirsuitabilityandapplicability.2.LiteraturereviewFactorsaffectingdamage,whethercontrollableoruncontrollable,shouldbejudiciouslystudiedinordertoachievesmoothandundamagedrockwalls.Theuncontrollableparametersofrockmasscomprisepetro-graphicstrataconditionsandgeo-technicalstrengthpropertiesofrock.Thecontrollableparametersareblastpattern,initiationsequence,powderfactor,explosivecharacteristicsanddistributionofexplosivewithintheblasthole.Blastingdamageofperipheryrockwallscannotbeavoidedbutcanbeminimizedtoareasonableextentbytheimplementationofasu