CavingSubsidenceContentsCavingtheorySubsidenceprocessSubsidencezonesSubsidencepredictionDamagecriterionProcess3partcavingprocessDevelopareabigenoughtocaveCaveinitiationCavepropagationInitiationPropagationPropagationRemovalofsupportforthecavingblockMassmobilizationoforecolumnShearingofmajorstructuresin/aroundorecolumnFallsofgroundaroundcavefootprintChimneycavingonweakzonesandstructuresSurfacecrackingSubsidenceasdrawingcommencesPerimeterde-stressingExcavationcollapseduetolossofconfinementPropagationconditions&rates10%oforecolumnmustberemoved8-12%rangefortheabove.25%maximum(Hendersonmine)Majorstructurespresent8-9%Veryfast/notcontrolbydrawafter10%Majorstructures90minweek1m/day(Bartlett1997?)VoiddiffusionnotswellSubsidenceprocess1.Propagatethecavetosurface2.Centresubsidence3.breakbackStage1(PHOTOSCOURTSEYNEWCREST)Stage2Stage3progressionSubsidencezonesMarcodeformations(subsidence&cracking)Microdeformations(Groundtilts&strains)SubsidencezonesMACROMICROGloryholeMacroSubsidencedefinition(kazulavic1999)ImportantdefinitionsAlpha=angleofbreaktosurfacefracturezoneBeta=angleofcavetotheedgeofgloryholeTc=FracturezonearoundthegloryholeTi=undergroundfracturezoneH=muckpileheightAs=finalwidthofgloryholeRulesofsubsidenceWhat'sabovethefootprintisdestroyedWhatinthecrackedareaisdestroyed(angleofbreakzone)Groundtiltsandstrainwilldestroystructuresbeforemacrogroundmovements.Whatneedstobeknownis:-largestfootprintoutlineprojecttosurface-Angleofbreak-Microdeformationalzone-criticaltilts&strainsofstructures/excavationsMacro/angleofbreak/cavedefinitionAngleofcaveisaFunctionof-Rockmassstrength-Muckpilesupport(H)-Depthofore\body-Majorstructures-Rockmass\shearstrength-HoopstressesAngleofbreak=angleofcave+perimeterfracturezone(Tc)AngleofcaveHastheirbeenanopencutOpencutassumeAngleofbreakNoopencutCavebelowopencutSlopedesign=c=0CavebreakangleCavebreakanglemethodsonlyAngleofbreakopencutHainesandTerbruuge1991slopeangledesignRockmassstrengthadjustedforcohesionlossduetocavingAngleofbreak/cavingExperiential(Scope)-45degreesor70degreesangleofbreakEmpirical(Define)-Laubscher1990,1997-Kavularvic1999Structural(adjustment)-modifiesgloryhole-Enlargesgloryholes-Structuralsurvey-Deterministicanalysis(Stacey&Swart2001)Laubscher(empirical-1993)ConditionDepth(m)AdjustedMRMR9070503010Nolateralrestraint10080706050405007060504030Lateralrestraintfromcavedmaterial10090807060505008070605040Laubscher(empirical-1997)Kavularvic-1997Structuraladjustment(Stacey&Swart2001)MICRO/NumericalMAP3D,FLAC2&3D,UDEC,3DECConfirmgloryholepositionModelstresseffectsFracturezoneGroundtilts&strainsaroundholeInfluenceofstructures-FLACStructuresreducegroundstrainsExcavationstresschange(10Mpa?????)Deformations(Stacey&Swart2000)Numerical(Kayetal1991)MicrozonedamagecriterionShafts-SouthAfricancriterionBuildings-UKSubsidenceengineershandbook1975MechanicsandconcreteworkfailfirstFanfoundationsReinforcedcollarscansustainmajordamageFoundationsstrongtowithstandtilts&strainsFoundationsflexibletowithstandgroundmovements.ShaftdamagecriterionTable22Damagecriteriaforshafts(modifiedfromMcKinnon,1989)TypeofdamageCriterionReferenceUnspecifieddamagezi<17MPaWilson(1971)Unspecifieddamage,criterionnotbasedonbackanalysiszi<1x10-3Salamon(1974)zi<1x10-3Wagner(1985)zi<1x10-3Daemen(1972)ti<1x10-3Wagner(1985)Steelworkdamageandincreasedshaftmaintenancezi<0,2x10-3Wilson(1971)zi<-0,4x10-3VanEmmenisandMoreO’Ferrall(1971)zi<0,4x10-3Esterhuizen(1980)Tensilefractureofconcreteliningzi<-0,51x10-3to-0,3x10-3Kratzsch(1983)zi<-0,2x10-3Budavari(1986)Compressivefractureofconcreteliningzi<0,7x10-3JagerandRyder(1999)S