自然崩落法(FREE-CAVING) -BLOCK CAVING Geotechnical培训

(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-Extractavoidtoallowcavingto occurTheundercutsizetoinitiatecavingisrelatedtotherockmassqualityandhydraulicradiusAweakerorebodyrequiresasmallerhydraulicradiusHydraulicradiusofbetween8mand35mnormallyrequiredUndercuttingaimsAIM2-Initiatecavingwithminimum damagetorockmassAimrelatestostresscontrolStressmagnitudesincreaseasundercutsizeincreasesStresscontrolrelatestothepercentageofcavinghydraulicradiusextractedUndercuttingaimsAIM3-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/stressregime narrowundercuts–high stressesSkilllevelofcrews mostcriticalaspectTechnology 3rdworldcountriesRequireblock productionmethodtonnageUndercutheights stressdamage–low

tons–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/monthUndercutdrawcontrolTopreventtheoverorunderdrawofblasted

groundincreasedstressesduetoremnantpillarscausedbychokeblastconditionscrushingoftunnelsinthecountryrockduetohighdrawratesfromdrawpointsslowratesofadvance,cavedground

floodingundercutlevel

drawpointmouthsmuckpilestackingduetounderdrawUndercutdrawcontrolUndercutdrawTrytodrawswellonlyDonotdrawmorethan100%ofringtonnageDrawacrosstheundercutshouldbe40-70%ringtonnageExtractionleveldesignDrawiskingInteractivelayoutsStress/fragmentationcut-offforuseSoftcavesheavysupportHardcaveslimitedsupportExtractionlayoutsExperientialNorthAmericaSouthAfrica/ZimbabweChileMRMRBinsforinteractionExtractionlevellayoutTypesDesignaspectsDrawbell/pointspacing -

MRMR -ICSMRMRprogram -PFC -Sandbins/physicaltests -experience

DRIVES/CAMMELBACKS/BREAKAWAYS

-spans -pillars -experience -NumericalmodelingSupport -MRMR -Experience -Modeling -DeterministicDrawlayouts1.5IFAIMDrawbellinteractionExperience5recentcavesDrifts4.2mX4.2mDriftspacing28-34m(30m)Drawpointspacing14-18m(16m)Offset-herringbone-r