CAVABILITYContentsBasiccavingtheoryCavingstresscycles/burstingTypesofcavingCavabilityassessment/DEESAMethodBasiccavingmechanics3partcavingprocessDevelopareabigenoughtocaveCaveinitiationCavepropagationPre-cavingCaveinitiationInitiationmechanismsTaylor(1980)TensilefailureShearfailureCompressionalfailureInitiationmechanics/tensionTensioncontinueTensioncontinueShearfailureCavingInitiationconditionsTaylor(1980)Jointdensity(combinationofflatandsubverticaljoints)MagnitudeandorientationofprinciplestressesHighlateralstressesinstrongrockinhibitcavingLowconfiningstressesallowtensilefailureTheimportantofrockstrengthincreasesasthenumberofjointsdecreaseCompressionalfailureoftherockdecreasesastherockincrease.PropagationCavingzones(Duplancic&Brady1999)CavingstresscycleCavingstressesSLC/BlockcavestresscyclesTimeStressBlockcaveSLCStressdropatpropagationNumberofcyclesCavingstressesRelatedtoareaneededtocausecavingStressincreaseafter50%aboveareaStressatmaximumatarearequiredforcavingUC/PRE-BREAKCRUSHINGAFTERCAVINGAREAHydraulicradiusAreaofundercut/SLCpre-breakPerimeter=HydraulicradiusHydraulicradiusFluidmechanicsOriginsunclearMASSMIN2000pg35to38ShapehasamajorinfluenceoncaveHRisashapefactorRoundorsquareshapegoodforcavingRectangularbadshapeIncavingHRisnormallythereqcavingHRHRisrelatedtorockmassqualityorexperienceCavingstressesDifferentstressregimeIncreasesanddecreasesovertimeStressesdecreaseaftercavepropagationSLCsoftcavedepthcut-off1000mBCsoftdepthcut-off1500mHR>28difficultafter1000mSLCde-stressing2yearcyclesCriticalHR+10%orereservedrawPitsubsidenceDriftdamage,1KDepth,MRMR35-45HR28Rock/strainburstingStressincreasesasundercutisdeveloped.Stressesincreasesfurtherbeforepropagation.PerimeterstressesincreasewithareaundercutandheightofundercutRock/strainburstdamagegreatestbeforepropagationRockburstingrelatedtocavingRockburstingrelatedtomanagementofcavingprocessRockburstcavepronecaves>300-400mHightectonicstressesMountainsMRMR>35DifficultyinpropagatedthecaveRapidratesofadvancesofpre-break/UCEl-Tiente1976RockburstingFracturedzoneexistsaroundthecave50mfromthecavefaceAsthecaveprogatesthiszoneincreasesFracturezoneincreaseduetostressrelaxationDuringthisstagesareasupto500mfromcaveeffectedStrainburstscanoccurinplaceslikecrusher,plats,cribbroomsStrainbursting,ejectionRockburstingBurstsoccurwithcavepropagationHighlevelsofseismisitybeforepropagation.MagofuptoRichter3.6Largecaveshaveupto6largeburstsifnotmanagedSeismiceventsduringpropagationareshearrelatedCommonareasforbursting20to40mfromcaveface/frontStrainburstingandrockejectionatbreakaways/intersectionsupto500mfromcave100mbelowthecaveLargeexcavationswith50mfromorebodyPillarsbetweenconferencingcavefrontsBeforepropagation.RockburstpreventionstrategiesMeshwalls/backsofintersections/largeexcavations500mfromcaveConeboltintersections/breakawaysInstallyieldingsupportwithin40mfrompropagationfacepositionReduceblockcavedrawrates<2000/tons/daybeforepropagationReduceblockcave/SLCpre-breakadvanceratesbelow3000m2/month.Propagatethecavefirst.SLC<45mvertical/m/yrMinetowardsthesolidCavepropagationThecavehasworkedStresseshavereducedBursthazardsarelessSignsSignsofPropagationsSurfacesubsidenceFallofgroundinworkingsRelaxedrockmassCavabilityassessmentDEESAmethodDoyouhaveaproject?ExperientialassessmentEmpiricalassessmentStructuralassessmentAnalyticalornumericalassessmentResultsfromallstagesmustcheckOrebodyhydraulicradiusCriticalhydraulicradiusExperientialCommonsensecheckChecksMRMRadjustmentsIsMRMRstressadjustment1TwotypesofcavesSoftcavesMRMR<45=HR19-25HardcavesMRMR>45=HR35-50EmpiricalassessmentEmpiricalSecondpassMRMR1990correlationData45,45Zone45MRMR,HR45AwayfromCaving/transitionlineStructuraltriggeringTruestructuralnaturenotaccountedforImpactofbackstressesareestimatedChallengeMRMRSystemchallengedTrueman&Mawdley(2003)ICSprojectNorthparkesexperienceDatadidnotcheckoutAdjustmentsquestionedNojustificationaboveMRMR50Depthcapofbetween500-1000m.K<2fora1000mNewsystemproposedbasedonmathewsmethodWhichgraphdoyouuse1989,1994?MathewsgraphMathews/MRMRgraphMRMRStabilitygraphdoeshavelimitationAllempiricalsystemshavelimitationsAsmuchexperienceasempirismsinMRMRmethodMRMRmethodhasworkedsince11yearsMathewsgraphusedMRMRdataforcavinglineMathewsmethoduntestedJrvaluescanleadtomajordifferencesinresultsProbabilitycontoursquestionedMathewsmethodAdvancedcavingknowledgeDefectsintheMRMRsystemLimitationsoftheMRMRsystemMoredataintransitionalzoneIsoprobablisticcontourconceptMathewcavinggraphStructuralcavabilityJointsandstressesImpactsofmajorstructuresImpactsofjointvariabilityMRMR20%HRadjustmentDeterministicanalysts‘J’BlockCHaSMMRMRstructuraladjustmentStructuralcavabilityJointsandstressesMRMR20%HRadjustmentDeterministicanalysts‘J’BlockCHaSMPlanofcavebackStructuralcavabilityNumericalModeleffectsofstressregimesImpactsofcavefrontadvancedirectionSensitivityrunsforstressandmaterialsShapeofundercut/