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UNDERGROUNDMININGMETHODSSummary：Thefirstsectiongivesanoverviewofundergroundminingmethodsandpracticesasusedcommonlyinundergroundmines,includingclassificationofundergroundminingmethodsandbriefexplanationsofthetechniquesofroom-and-pillarmining,sublevelstoping,cut-and-fill,longwallmining,sublevelcaving,blockcaving.Keywords:Miningmethod,undergroundmining,room-and-pillarmining,support,1UndergroundMiningMethods1.1ClassificationofUndergroundMiningMethodsMineralproductioninwhichallextractingoperationsareconductedbeneaththegroundsurfaceistermedundergroundmining.Undergroundminingmethodsareusuallyemployedwhenthedepthofthedepositand/orthewastetooreratio(strippingratio)aretoogreattocommenceasurfaceoperation.Oncetheeconomicfeasibilityhasbeenverified,themostappropriateminingmethodsmustbeselectedaccordingtothenatural/geologicalconditionsandspatial/geometriccharacteristicsofmineraldeposits.Considerationsinclude:1.Spatial/geometriccharacteristicsofthedepositconcerned:theshape,size,thickness,anddepth.2.Strengthofthehangingwall,footwall,andorebody.3.Economicvalueoftheoreandgradedistributionwithinthedeposit.Theselectionofundergroundminingmethodsisprimarilybasedonthegeological/spatialsettingofthedeposit.Candidatemethodscanthereforebechosenandrankedbasedonestimatedoperational/capitalcosts,productionrates,availabilityoflaborsandmaterials/equipments,andenvironmentalconsiderations.Themethodofferingthemostreasonableandoptimizedcombinationofsafety,economics,andminingrecoveryisthenchosen.Reflectingtheimportanceofgroundsupport,undergroundminingmethodsarecategorizedinthreeclassesonthebasisoftheextentofsupportrequired:unsupported,supported,andcaving.Unsupportedmethodsareessentiallynaturallyorself-supportedandrequirenomajorartificialsystemofsupporttocarrysuperincumbentloads,insteadrelyingonthenaturalcompetenceofthewallsoftheopeningsandpillars.Thisdefinitionofunsupportedmethodsdoesnotexcludetheuseofrock/roofboltsorlightstructuralsetsoftimberorsteel,providedthatsuchartificialsupportsdonotsignificantlyaltertheload-carryingabilityofthenaturalstructure.Thefollowingsareconsideredunsupportedmethods:•Room-and-pillarmining•Shrinkagestoping•SublevelstopingOftheunsupportedmethods,room-and-pillarminingisemployedforextractionofflat-dippingandtabulardeposits,whereasshrinkageandsublevelstopingareappliedtoverticalorsteeplyinclinedorebodies.Shrinkagestopinghasinthepastbeenverypopular,particularlyinnon-coalmining.Gravitycanbeutilizedfororetransportationandbrokenorestoredwithinthestopemayfunctionasaworkingplatformandtemporarywallsupports.Itwasquiteattractiveintheperiodbeforemechanizationbecamewidespread,whensmall-scaleoperationsonvein-typedepositsprevailed.However,withrisingcosts,thescarcityofskilledlaborandthetrendtowardmechanization,themethodhasbeenlargelydisplacedbysublevelstopingandcut-and-fill.Sublevelstopingwillthereforebetheonlyunsupportedmethodsexaminedindetailhere.Supportedmethodsrequiresubstantialamountsofartificialsupporttomaintainstabilityinexploitationopenings,aswellassystematicgroundcontrolthroughoutthemine.Supportedmethodsareusedwhenproductionopenings(stopes)arenotsufficientlystabletoremainopenduringoperation,buttheopeningrequiredtobeheldopentopreventcavingorsurfacesubsidence.Inotherwords,thesupportedclassisemployedwhentheothertwocategoriesofmethods,unsupportedandcaving,arenotapplicable.Thesupportedclassofminingmethodsisintendedforapplicationundergroundconditionsrangingincompetencyfrommoderatetoincompetent.Inthedesignofartificialsupportsystemstoprovidevaryingdegreesofcontrolledwallclosureandgroundmovement,anevaluationofload-carryingcapacityofthenaturalrockstructureisaprerequisite.Themostsatisfactoryformsofartificialsupportarebackfilling/stowing,timbers/stulls,andhydraulic/frictionalprops.Therearethreespecificmethodsinthesupportedclass.•Cut-and-fillstoping•Stullstoping•Square-setstopingCut-and-fillandstullstopingareintendedformoderatelycompetentrock,whereassquare-setstopingissuitablefortheleastcompetentrock.SupportedmethodshavedeclinedinusesinceWorldWarII,primarilybecausecut-and-fillstopingistheonlymethodthatlendsitselftomechanization.Stullstopingandsquare-setstopingareinfrequentlyusedandrelativelyunimportanttoday,becauseofexcessivelaborintensityandverylowproductivity,inadditiontoascarcityofskilledworkforcesandavailabletimberresources.Onlycut-and-fillstopingwillbedescribedlaterindetail.Cavingmethodsaredefinedasthoseassociatedwithinduced,controlled,massivecavingoftheorebody,theoverlyingrock,orboth.Theexploitationworkingsincavingmethodsaredesignedtocollapse,withintentionalcavingoftheoreand/orhostrock.Thethreemajorcavingmethodsare:•Longwallmining•Sublevelcaving•BlockcavingLongwallminingisusedinhorizontal,tabulardeposits(mainlycoal),whiletheothershaveapplicationsininclinedorvertical,massivedeposits,almostexclusivelymetallicornonmetallic.Becausetheexploitationopeningsareintentionallydestroyedintheprogressofmining,thecavingclassistrulyunique.Rockmechanicsprinciplesareappliedtoinducecavingratherthantopreventtheoccurrenceofcaving.Moreover,developmentope