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1、InternationalJournalofRockMechanics&MiningSciences39(2002)367–380Damageinarockcorecausedbyinducedtensilestressanditsrelationtodifferentialstraincurveanalysis1K.Sakaguchi*,W.Iino,K.MatsukiDepartmentofGeoscienceandTechnology,GraduateSchoolofEngineering,TohokuUniv
2、ersity,01Aramaki-Aza-Aoba,Aoba-ku,Sendai980-8579,JapanAccepted8April2002AbstractAfiniteelementanalysiswascarriedouttoanalyzethedistributionoftensilestresswithinandbelowalongHQcorestubfor77insitustressconditions.Themaximumtensilestressexperiencedbythecorealongthe
3、axisduringboringunderinsitustresswasaccumulatedinanequal-areastereonetforacentralpartofthecross-section.Themaximumtensilestressaccumulatedforacentralareaoflessthanabout60%ofthetotalcross-sectionalareawasconcentratedinacertaindirection,whichwasnearlythesamedirec
4、tionastheminimumprincipalstressforallofthestressconditions,exceptthoseinwhichtheminimumprincipalstress(s3)wasequaltotheintermediateprincipalstress(s2).Whens2¼s3;thedirectionofthecumulativemaximumtensilestresslayapproximatelyintheplaneofs2¼s3;whichisperpendicula
5、rtothemaximumprincipalstress.Basedontheassumptionthatapenny-shapedcrackisproducednormaltothemaximumtensilestressinproportiontothemagnitudeofsuchstress,thecrackdensityinthecorewasanalyzedbycalculatingstrainunderhydrostaticpressureasindifferentialstraincurveanaly
6、sis(DSCA).Themaximumprincipalcrackdensityinthecentralpartofthecorewasmuchgreaterthantheintermediateandminimumprincipalcrackdensities,excludingspecialcasesinwhichs2¼s3:Thedirectionofthemaximumcrackdensitywassimilartothatoftheaccumulatedmaximumtensilestress.Thus,
7、thedirectionofthemaximumcrackdensityobtainedbyDSCApredictsthedirectionoftheminimumprincipalstressratherthanthatofthemaximumprincipalstress,ifthedistributionofpre-existingmicrocracksbeforestressreliefisisotropicandifadditionalmicrocracksareproducedonlybytensiles
8、tressduringboringunderinsitustress.Toverifythis,crackparametersweremeasuredbyDSCAfortwocoresofquartz-diorite,whichweretakenbyovercoringwhenthehemispherical-endedboreholetech
