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1、InternationalJournalofRockMechanicsandMiningSciencesAnalysisofgeo-structuraldefectsinflexuraltopplingfailureAbbasMajdiandMehdiAminiAbstractThein-siturockstructuralweaknesses,referredtohereinasgeo-structuraldefects,suchasnaturallyinducedmicro-cracks,areextremelyresponsivetotensilestresses.
2、Flexuraltopplingfailureoccursbytensilestresscausedbythemomentduetotheweightoftheinclinedsuperimposedcantilever-likerockcolumns.Hence,geo-structuraldefectsthatmaynaturallyexistinrockcolumnsaremodeledbyaseriesofcracksinmaximumtensilestressplane.Themagnitudeandlocationofthemaximumtensilestre
3、ssinrockcolumnswithpotentialflexuraltopplingfailurearedetermined.Then,theminimumfactorofsafetyforrockcolumnsarecomputedbymeansofprinciplesofsolidandfracturemechanics,independently.Next,anewequationisproposedtodeterminethelengthofcriticalcrackinsuchrockcolumns.Ithasbeenshownthatifthelength
4、ofnaturalcrackissmallerthanthelengthofcriticalcrack,thentheresultbasedonsolidmechanicsapproachismoreappropriate;otherwise,theresultobtainedbasedontheprinciplesoffracturemechanicsismoreacceptable.Subsequently,forstabilizationoftheprescribedrockslopes,somenewanalyticalrelationshipsaresugges
5、tedfordeterminationthelengthanddiameteroftherequiredfullygroutedrockbolts.Finally,forquickdesignofrockslopesagainstflexuraltopplingfailure,agraphicalapproachalongwithsomedesigncurvesarepresentedbywhichanadmissibleinclinationofsuchrockslopesandorlengthofallrequiredfullygroutedrockboltsared
6、etermined.Inaddition,acasestudyhasbeenusedforpracticalverificationoftheproposedapproaches.KeywordsGeo-structuraldefects,In-siturockstructuralweaknesses,Criticalcracklength1.IntroductionRockmassesarenaturalmaterialsformedinthecourseofmillionsofyears.Sinceduringtheirformationandafterwards,t
7、heyhavebeensubjectedtohighvariablepressuresbothverticallyandhorizontally,usually,theyarenotcontinuous,andcontainnumerouscracksandfractures.Theexertedpressures,sometimes,producejointsets.Sincethesepressuressometimesmaynotbesufficientlyhightocreateseparatejointsetsinr