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Computermodelingofdynamicgroundmotion dueto explosiveblastingandreview ofsomemodelingproblems

Chamg･HaRyu★

NumericalmodelinglSanapproximatemethod.Thevalidityofthealgorithm usedinthe numericalmethodShouldcarefullybeinve8tigatedbyprovidingwhetherthecalculations performedbythemethodyieldtheresultsthatareacceptable.Anewteclm iquewasdeveloped topredictthedynamicmotionorgroundinducedbyblasting,whichutilizedthefiniteelement analysis,coupledwithnon･parametricsourceidentificationmethod.Theresultsgivethe informationonthefrequencycharacteristicsofgroundmotionaswellasvibrationlevels.For t

hevalidityorthemethod,measuredgroundmotionswerecomparedwithestimatedoneS.Good agreementwasshownbetweenmeasuredgroundmotionandthatcalculatedbythesuggested method.Someproblemsinvolvedinthenumericalmodelingwerealsoidentified.

1.Lntroduction

ExplosiveblastinghasWidelybeenusedinthe rleldsofmining,Civilandconstructionengineering aSatoolofrockexcavation.Whilethepast researchesontheblastingquitedependedonthe empirical,andtrialanderrorb88edmethods,the developmentornumericalandexperimentaltools makesitpossibletotakescientificapproachto higherlevelofblastingtechnique.Thecontrolled blastingLab.,oneortheNationalReさeareh LaboratoriesinKorea,iSaunlqueSPeCiali乞ed groupinexplosiveblastingandhasperformedquite extensiveresearchprojects.Oneoftheinteresting researchesWastOdevelopatechniqueforthe predictionordynami cgroundresponse.Various kindsofnumericaltoolsareavai)ablethesesdays, andeachhasitsownmodelingcapabilityand80me limi tationsindynamicmodeling.

2.Dynamic response of ground induced by bJast loading

Received:May17,2002 A∝epted:October8,2002

*KoreaInstituteofGeoscience&Mineral Resources,Daejon305･350.KORZiA

ProjectManager,ControlledBIastingLab.

TEL:+82‑42‑868･3236 FAX:+821JI2‑861･972I e･mail:cIyu@kigam,re.kr

Aneces姐rypartOftheplannlngOfconstruction blastingoperationsistheestimationofpotential damagetonearbyStruCtureS.Thenoiseandthe vibrationstransmittedthroughthegroundmay alsoaffectthepeoplearoundablastsite.These vibrationsandtheaccompanylngnoiseareoften anannoyancetothepeoplelivingandworkingnear ablastingoperation.Comp18intS8SSOCiatedwith blastinghaveoftenbecomeAtargetOfpublic grleVanCeSinKorea.However,carefulcalculations andplacementoftheexplosivescancontrolthese adverseeffectsofblasting.

2,1Predictiveequation

Theground motioncan bemeasuredas displacement,velocityoraccelerationofaparticle intheground.KoreahasnOnationalStandardyet fortheacceptancelevelofblast･inducedground v

ibration,butpeakparticlevelocitycriteria,which wasSuggestedinSeoulsubwayconstruction,has oftenbeenwidelyused.Itisthecriteriaderlnedby peakparticlevelocityonlyregardlessorthe frequencycontenLPredictionofgroundmotionin particlevelocitymaybemadewithoutdifrlCulty from thetestblasting.Inpracticaluse,peak particlevelocityCanbeplotteda8afunctionor scaleddistanceofwhichconcepti8Scalingthe distancefromablastbyexplosivechargeWeight.

KayakuGz)kkaishi.Vol.63.No.5,2002 ‑217‑

Themostgeneralform usedinKoreBSforthe predictionof酢OundvibrationSiBABfollows:

pw‑K(%^TorK(A)^{‑ ,.,}

whereFPVisthepeakparticlevelocityincmSeC

IorJnm SeC■●,WisthechargeWeightperdelayin kg,Disthedistancefrom ablastsourceinm.

Propagationcharacteristicsareinnuencedbyrock properties,geologicaldiscontinuitiesandbla8t designparametersSucha8Chargeweight.distance f

romthesource,blastpattem,and800n.Although thoseeffectsArereflectedtothecoupleofcon8tant8, KAndA,intheequation,itallowsuStOtakevery practicalwayforprediction.

Whilethepeakparticlevelocityhasbeen SuggeSteda8thebestde8Criptortoa88e88the damagepotentialofstructures,velocityitselfi8 notSufficienttoevaluateStructuraldamage withoutconsideringtoleranceOfthe8truCturel川 .

BecausestructuresresponddimerentlytovibrationS ofdifferingfrequencycontent,frequencycontent hasbecomeanincreaslnglyimportantparameter inthemeasurementAndanaly8i80fground v

ibrationsfromblasting.BasedontheanalySi80f extensivetechnicaldata,theformerU.S.Bureau ofMines and Office ofSurface Mining recommendedrevised8afebla8tingvibration criteriaforresidentialstructures,dependingon thepeakparticlevelocityvarylngwithrespecttO thefrequencyS)･ThecriteriaincorporateAn importantelementofreSpOnSeSpectratechnique insomere8PeCtS.TheGermanvibrationstandard, DIN4150,isalsoof8imilarformforseveraltypes ofstructureBG).InordertoasSe88thedamage problem8usingthepeakparticlevelocityassociated w

ithpredominantfrequencies,itisneceSBArytO gettheinformationonthehistoryOfgroundmotion aswellaspeaklevelofvibration.

Onehasageneraltendencythatatclosein distancesfrom a blast,high frequencies

predominatethevibrationrecordAndthatlow frequenciesdofarfromablast.However.wefailed togetthegeneralforrnulaliketheSCaleddistance equationforpredictingthefrequency.Evenifthe basicinformationforprelimi narydesignpurpose isacquiredfromthetestblasting,itmaybequite differentfrom whati8 meaStlred during constructionblastingduetothechangeinblast condition,media,etc.ItiSalmostimpo$8ibleto consideralltheparametersexperimentallyinthe deさignstage.Inthisregard,numericalmodelirlg isaveryt鳩efultooltoasSeSSmostpOSSibilitie8 thatmayoccur.

2.2Numericalrnodeling

Oneofthenewteclm ique8Wasdevelopedby utiliZiingthefiniteelementanAly8iB.COupledwith non‑parametricsourceidentificAtiorLmethod.The basicconceptisasfollows.Therelationshipbetween lnputsourceandresponseinalinearBy8temWhere principlesofsuperpositionareappliedcanbe expressedas:

tqL'aJ=H(L'aJIYJ'aI) (2)

whereL7()'az)andPGaJarecomplexFourierSpectra ofresponSe,Ln(i),AtapointandinputmotionP(i), respectively;H()'al)istransferfunctionderlningthe relationshipbetweeninputandresponse;alis frequency;andJ'i8+^{I.Becau8eequation(2)is}

composedoffrequencydependentthreecomplex function8,OneOfthefunctionscambeeasily determinediftheothertwofunctionsaregiven.

W

h entJ()'aJandH(J'aJaregiven,80urCefunction, PGLu),i8CalculatedaSfollows:

H(･･0,‑芸浩 一 p･･.a,‑% (3, InordertoreduceerrormoreeLricientlyinvolved ine白timatingthefrequencyre8pOn8efunction,a computerprogram calledKIESSIwasusedto determi nethefunction7).Inordertocalculatea transferfunction,HGL27),thegroundiBmodeledas TabJe1Inputdata0fphysicalpropertiesusedforanalysis

Shearwavevelocity Poisson.S Density Damplngra tio (m/see) ratio (dc

c) (%) G.L.0‑.2m 2,100 0.2

4 2.55 2.0 G.L.‑2m 一一4m 2,200

0.25 2.57 2.0 G.L.<‑4m 2,300 0.33

蛋 20m 40m 50m 60m 80 m

≡≡≡≡≡ :iiiiiiiiiiiil

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Fig,1Finiteelementmeshandblastmode.i:1･g

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(a)horizontalgroundmotionat20m (b)verticalgrollndmotiona t60m

Fig.2Fouriertransformofvelocityhistory

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0.10 0.2Ti0me(BeC0).30 0.■O EI.50 Fig.3 VelocityhistoryOfvertical

groundmotionat60m, calcuhted

fjaS J)一ul∈J

^ 0.00 0.10 0.20 0.10

Tim8(8eC) ≡≡n^{……L ーeasLlTed巴 ｡5,}

Fiど.4Velocityhistoryofhorizontalgroundmotion8t60

m,

rneastlred

ShowninFig.1whereaxisymmetriC丘miteelements surface.h adissimplifiedt

oactinthehorizontal coupledwithinfiniteelement

holesinthefield.Majorgroundpropertiesarelisted inTablelPI.

2.3Fieldmeasurement

Groundmotionsweremeasuredthrough tesL blastsperformedattheTangJinpowerplant constructionsite.Geophoneswerelocatedat20, 40,50,60,80m from theblastsource,andtime hiStOrieSforvelocityweremeasuredinbothvertical andhorizontaldirections.Estimationoftheblast sourcewascarriedoutusingthemeasured vibrationrecordateachlocationandthetransfer functionwascalculatednumerically.Theresults glVe the information on the frequency characteristicsofgroundmotionaswellas vibrationlevels.Forthevalidityofthemethod, nleaSuredgroundmotionswerecomparedwith

LOB AZB Ad 0.00 AGEI 1.0D

uD

Freq.(rtz) estimatedones.Figure

s2‑4Showtheexamplesor 8electedresu)ts.The

frequencySpectrum Ofthe verticalgroundmot

ionat60m from theblast sourceshowsonlyabou

t5H21differenceinpeak Frequency(母eeFig

ure2b).Goodagreementin generalwasSho

wnbetweenmeasuredground motionandthatCalculated

bythesuggested method

.

2.4NuTheprmerjoblcalprem.howevoblems

er,liesinthecalculated sourcebehaviora8Shown

inFig.5.Itlooksquite differentfrom therealbl

ast80urCe,i.e.ithasno physicalmeaning.S

omecalculationsusingthe FLACShowedgroundre

SpOnSeSdinTerentfromthe measuredoneor80met

imesnumericalinstability whenthepressureorexplosiveloadingcalculated

OJM 1.○○ ZJeO )JP 4bg I.00 ●14 7m

(a)UnstableArchexAmple (b)Limi tingfrictionState(Kn=jointnormal 8tirrne8S.KS≡jointShear8tifrne88)

Fig.7Analy8i80rlimi tingfrictionstateforunsta

blearchmesh bysomeequations8ugge8tedinate

xtbookwas applied888boundaryCOnditionlII･one

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basedanaIy8i8maybehowlo

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ockmfIB8.TheefrectBOr fracturingandenergylo8SA

S^B∝iAtedwithitmust be reflected to theboun

dary COndition8.

ComparisonOftheresultsbetwee

nFieldSCale experimentorexplosivedemolition

ofconcrete columnsandnumericalmodelingusingthe ANSYSb88edonFiniteElernentmethodwas Carriedout.Rea80nableresultw88Obtained

for calculationorcr8Ckgrowthwiththe8i之eOr

the loadingreducedtDaboutonethird.(βeeFi

g.6)The soundunderstandingorvari8ble8Andc

onBtitutive equationderiningdynamicbehaviorwo

uldbe anotDiherkestinctelyseme. nttechniqu

ei8OneOrthepowerful numericaltoolsformodel

ingtherockm86S responseinlaterStageOr

blasting.Majorinput variable8relat.edI.omat.e

rilllchllrnCt.eri8tic8are jointpropertiesand

damplngintheanaly^Si8^.The slgniricAnCeOrjoint8

tirrne88h88notbeenpaid muchattentionin

mostPrevious8Ludie80日he distinctelemen

tmethod.Somenumericalre8ultS calculatedbyaDi

stinctElementcodeb88edon implicitalgorithmShow

edthattheStabilityorarCh tunnelwasindependen

torjointSLirfne88ratio(Bee Fig.7).Butotherresu