PPT 自然崩落法（全英文）10

(FREE-CAVING)-BLOCKCAVINGGeotechnicalContentsTypesofcavesUndercutdesignExtractionleveldesignBCgeotechissues2CAVETYPESHARDCAVES(MRMR>45,1000mdepthKratio1-2)CavestallFragmentationRock/strainburstingSOFTCAVES(MRMR<45,1000mdepth,Kratio1-2)Excavationlevel&UCstressinduceddamageUndercutcrushingStrain/rockburstingwhenMRMR>35RULESStrategicdesignControlgeotechnicalriskswithUCSupportistacticalissueMainissues-undercutdesign-extractionleveldesign-drawcontrolUndercuttingStressandburstprotectionmethodDowehaveafragmentationproblem?Dowehaveastressproblem?Weneedtoknow:StartpositionUndercutretreatdirectionCriticalHRStrategyGeometry“undercuttingisprobablyoneofthemostimportantofalltheactivitiesinvolved.Therefore,thecorrectdesignandmanagementoftheundercutiscriticaltothesuccessoftheblockcave.”BlockcaveundercuttingUndercuttingAimsUndercutStrategiesManagementConfigurationControlDrawControlPrePostAdvancedExtractionmethodFanFlatInclinedLags/LeadsBlastDrawAIM1-ExtractavoidtoallowcavingtooccurTheundercutsizetoinitiatecavingisrelatedtotherockmassqualityandhydraulicradiusAweakerorebodyrequiresasmallerhydraulicradiusHydraulicradiusofbetween8mand35mnormallyrequiredUndercuttingaimsAIM2-InitiatecavingwithminimumdamagetorockmassAimrelatestostresscontrolStressmagnitudesincreaseasundercutsizeincreasesStresscontrolrelatestothepercentageofcavinghydraulicradiusextractedUndercuttingaimsAIM3-AdvanceHRtoreducestressesRequiresundercuttoadvancefromweakertostrongergroundPropagationofcaverequires8-12%drawofblockreserveFulldestressingnormally25-30%ofblocktonnageisdrawnTunnelsmaybesubjectedtoundercutabutmentstresseslongerUndercuttingaimsUndercutextentStressconditionRemarks25%ofHRLowLimiteddamage50%ofHRBecomingaconcernOnsetofcriticaldamage75-110%ofHRMaximumSeveredamageSupercaves(MRMR>45):Stresslevelbecomesaconcernforextraction>75%ofHRUndercuttingAimsUndercutStrategiesManagementConfigurationControlDrawControlPrePostAdvancedExtractionmethodFanFlatInclinedLags/LeadsBlastDrawUndercuttingstrategiesPreundercuttingReducedstresses,productiondelays,compactionremnantsPostundercuttingFasterproduction,stressinduceddamage>60%extractionratio-severedrawhorizondamage,500moperationlimitAdvancedundercuttingLimiteddrawhorizondamage<60%criticaldrawhorizonextractionlimitStrategiesUndercutdevelopedbeforedrawhorizonAdvantageReducedstressdamagePREUNDERCUTTINGStrategiesDrawhorizonfulldevelopedthenundercutAdvantageBlockbroughtintoproductionquickerDisadvantagesDrawhorizonstressinduceddamages,driftrepair,productiondelaysPOSTUNDERCUTTING(conventional)StrategiesDrawhorizondamagerelatestostressmagnitudeanddrawhorizonextractionStressmagnitude2-3timeshigherthanthepre-undercutlevelsSeveredamageoccursat60%drawhorizonextractionCollapseoccursat80%drawhorizonextractionLimitingoperationaldepth±500mPOSTUNDERCUTTING(conventional)StrategiesLimitedamountofdevelopmentondrawhorizonbeforeundercuttingDriftsbeforeundercut,crosscutsanddrawbellsafterundercutKeepdrawhorizonextraction<60%(Butcher1999)ADVANCEUNDERCUTTINGStrategiesAdvantagesdrawhorizondamageisreducedthecaveisbroughtintoproductionquickerthanwithapre-undercuttingstrategyaseparatelevelisstillrequiredforundercuttingthisstrategyisslowerthanpostundercuttingDisadvantagesSomedrawhorizonSlowerthanpostundercuttingADVANCEUNDERCUTTINGUndercuttingaimsAIMS––Whatarewetryingtodo?ExtractavoidtoallowcavingtooccurInitiatecavingwithminimumstressdamagePropagatethecavetoreduceundercutabutmentstressesUndercuttingAimsUndercutStrategiesManagementConfigurationControlDrawControlPrePostAdvancedExtractionmethodFanFlatInclinedLags/LeadsBlastDrawExtractionmethodsCONSIDERATIONSDepth/stressregimenarrowundercuts–highstressesSkilllevelofcrewsmostcriticalaspectTechnology3rdworldcountriesRequireblockproductionmethodtonnageUndercutheightsstressdamage–lowtons–highExtractionmethodsBlockcavefanundercutwithoutseparatelevelExtractionmethodsConceptualPlanofflatundercutshowingpossibleproblemareasExtractionmethodsInclinedundercutpotentialproblemareasUndercuttingAimsUndercutStrategiesManagementConfigurationControlDrawControlPrePostAdvancedExtractionmethodFanFlatInclinedLags/LeadsBlastDrawUndercutmanagement“Managementisprobablyoneofthemostneglectedaspectsofblockcaveimplementation;withundercuttingproblemsbeingduetopoormanagementratherthandesign”UndercutmanagementLagcontrolUndercutfrontlagdistance(caveline)UndercutfrontstressconditionDamage<5mIdealMinimum8mModerateModerate10-12mHighSevere>12mVeryhighUndercutfrontcrushingSupercaves–12-18mlagstoleratedto75%HR<12mlagsfrom75%HRUndercutmanagementLagcontrolUndercutstage

(%ofrequiredHR)TolerablefacelagdistanceConfigurationreviewperiod0-25%5-8m7-14days25-50%5-8m7-14days50-75%5m7days75-100%2-5mDailyUndercutmanagementRateofadvancesAdvanceasrapidlyaspossibletoHRwithoutincurringproblemsReducerateofadvancefromHRCavetons>undercuttons-preventarchinducedabutmentcrushingRateofadvance±2300m2/monthUndercutdrawcontrolTopreventtheoverorunderdrawofblastedgroundincreasedstressesduetoremnantpillarscausedbychokeblastconditionscrushingoftunnelsinthecountryrockduetohighdrawratesfromdrawpointsslowratesofadvance,cavedgroundfloodingundercutleveldrawpointmouthsmuckpilestackingduetounderdrawUndercutdrawcontrolUndercutdrawTrytodrawswellonlyDonotdrawmorethan100%ofringtonnageDrawacrosstheundercutshouldbe40-70%ringtonnageExtractionleveldesignDrawiskingInteractivelayoutsStress/fragmentationcut-offforuseSoftcavesheavysupportHardcaveslimitedsupportExtractionlayoutsExperientialNorthAmericaSouthAfrica/ZimbabweChileMRMRBinsforinteractionExtractionlevellayoutTypesDesignaspectsDrawbell/pointspacing-MRMR-ICSMRMRprogram-PFC-Sandbins/physicaltests-experienceDRIVES/CAMMELBACKS/BREAKAWAYS-spans-pillars-experience-NumericalmodelingSupport-MRMR-Experience-Modeling-DeterministicDrawlayouts1.5IFAIMDrawbellinteractionExperience5recentcavesDrifts4.2mX4.2mDriftspacing28-34m(30m)Drawpointspacing14-18m(16m)Offset-herringbone-reduced