采煤专业外文翻译土压力理论在薄煤层回填支柱设计中的应用Word文件下载.docx
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采煤专业外文翻译土压力理论在薄煤层回填支柱设计中的应用Word文件下载.docx
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1.Introduction
TheSelf-AdvancingMinerhasbeendesignedtoextractcoalfromseamslessthan90centimetersthick.TheSAMallowsforextractionofthefullseamheightwhileminimizingwasterock,andutilizesremoteoperationthatallowstheminertoadvanceupto180m(600ft)intotheseam.However,thecoalseamsaresothinthattherecoveryratesofthisminingmethodwillbefairlylowandwilldecreaserapidlywiththedepthofmining.Inordertoincreasetherecoveryfromthin-seammines,pillarsmustbedesignedassmallaspossiblewithoutcompromisingthestabilityofthemine.Backfillcanprovidethesupportnecessarytomaintaintheintegrityoftheundergroundworkingswhileallowingforincreasedextraction.
Theplacingofbackfillundergroundhaspredominantlybeenapracticeemployedincut-and-fillmines(Thomas,1979).Backfillmaterialisintroducedundergroundintopreviouslyminedstopestoprovideaworkingplatformandlocalizedsupport,reducingthevolumeofopenspacewhichcouldpotentiallybefilledbyacollapseofthesurroundingpillars(Barretetal.,1978).Thepresenceoffillinanopeningpreventslarge-scalemovementsandcollapseofopeningsmerelybyoccupyingvoidsleftbymining(Aitchisonetal.1973).Therefore,theplacementoffillinopenspacesundergroundtendstopreventtheunraveling/spallingofthesurroundingrockmassintothemined-outspace,effectivelyincreasingthestrength,orloadbearingcapacity,ofthesurroundingrockmass.Thistypeofsupportmechanismnotonlyhelpsprovidesupporttopillarsandwalls,butalsohelpstopreventcavingandrooffalls,minimizesurfacesubsidence,andenhancepillarrecovery(Coates,1981).
Althoughthesupportcapabilityofbackfilliswellknownitstillremainsfairlydifficulttoquantify.Modelsandequationsforthedeterminationofbackfillsupporthavebeenproposed(Cai,1983;
Guang-XuandMao-Yuan,1983)andpillar-backfillsystemshavebeenmodeledusinglaboratoryset-upsinordertocorrelatetheactualsupportbehavioroffillwithproposedmodels(YamaguchiandYamatomi,1989;
BlightandClarke,1983;
SwanandBoard,1989;
Aitchisonetal.,1973).Butingeneralthesemodelsandlabtestsaredependentonlocalexperienceandempiricallyderivedrelationshipsbetweenbackfillsupport,materialproperties,andminegeometry.SincetheSAMisstillindevelopmentthereisaneedforasimpleandreliablemethodofestimatingthemagnitudeofsupportprovidedbybackfillbasedonexistingknowledge.Itisproposedthatclassicalearthpressuretheorycanbeusedtoestimatethelateralearthpressureappliedbybackfill.Theanticipatedbehaviorandresponseoffilltodeformationsofthesurroundingpillarsandroofareanalyzedhere.Thesupportingeffectofbackfillisincorporatedintotheoriginalpillardesign(unsupported)sothatnewpillarwidthscanbecalculatedandtheincreaseinrecoverycanbedetermined.
2.Thethin-seamcoalmine
Athin-seamcoalmine,employingtheSAMtechnology,canbethoughtofasan‘underground’highwallmine.Figure1depictsthesimplifiedpanelgeometrycreatedbythedevelopmentofentriesandcross-cuts,andthesystemofpillarsleftbehindafterpanelextraction.Itisprobablethatthe
cutsandcross-cutswillbeangledatapproximately60soastodecreasetheturningradiusofminingequipment,butthiswillnoteffectpillardesign.Thelengthofeachpanelis1200m(4000ft).Thewidthofeachpanelvarieswithdepthinordertoaccommodateabarrierpillarthatrunsthroughthecenterofeachpanel.However,thepanelwidthwillbeatleastGreaterthantwicethedistancerequiredforoneSAMcut,inthiscase300m(1000ft).Uponextractionofthepanels,thebarrierpillarandaseriesofpillarsleftbetweencutsremainineverypanel.Largebarrierpillarsarealsoleftattheendsofthepanelstoprotectthecross-cuts.
Figure2isacross-sectionalviewofthecuttingface.Thefaceevokesthehighwallminecomparison;
thecoalseamrunsthroughthemiddleofthepanelandaportionofthepanel‘material’isleftaboveandbeloweachcut.Thecutwidthis3m(10ft)andthecutheightisequivalenttotheseamheight(lessthan90cm(36in)).ItisintendedthatastheSAMretreatsfromeachcut,backfillwillbeeitherhydraulicallyorpneumaticallyplacedinthemined-outvoid.
3.Applicationofearthpressuretheory
Theideathatthebackfillsupportmechanismdescribedintheprevioussectioncanbequantifiedusingprinciplestakenfromsoilmechanicsisnotnew.Abroadunderstandingoffillbehaviorhasalwaysbeendependentonknowledgeofearthpressures.However,earthpressuretheoriesandconceptshavenotgenerallybeenconsideredadequateinproperlyquantifyingthemagnitudeoffillsupportinundergroundmines.Limitedunderstandingaboutthetransferofloadsfromthesurroundingrocktothefillandfrictionaleffects,alongwithminegeometry,havemadeitdifficulttoapplytheconceptsofearthpressuretheorytobackfillsupport(Thomas,1979).
WhatmakesthecaseoftheSAMoperatinginathin-seamcoalminedifferentistheconceptof‘designedfailure’ofthepillarssothatdeformationscapableofmobilizingthepassiveresistanceofthebackfillwilloccur.Fromcivilengineeringdesignofretainingwallsithasbeenshownthatthemovementrequiredtoreachmaximumpassiveearthpressurewithininaloosesandysoilis4%ofthewallheight(CloughandDuncan,1971).Thedenserthesoil,thelessmovementrequired.Applyingthisguidelinetothethin-seamcoalmine;
forapillarheightof90cmlateraldeformationofthepillarmustbeatleast3.6cmforaloose,sandybackfilltoreachmaximumpassiveearthpressureconditions.Theinitialstagesofpillarfailuremaynot
producemovementsthatlarge,butovertimecreepdeformationwillalmostcertainlyproducemovementslargeenoughtoinitiatefullpassiverestraintwithinthebackfill.
Verticalloadingofthebackfillbytheimmediatefracturedroofstratacaneasilybeincorporatedintoearthpressuretheory.Theweightofthecavedmateriallyingonthefillisequivalenttoasurchargeload.Overtime,bulkingofthecavedmaterialresultsinaverticalloadequaltotheoverburdenpressure.
Frictionbetweenthepillarandfillwillhaveanimportanteffectonthemagnitudeofthepassivepressureappliedbythefill.Itisexpectedthatthefrictionbetweenaspallingcoalpillarandgranularfillmaterialwillbequitehigh.However,frictionaleffectscanbeaccountedforinearthpressuretheory.
4Usefulnessofbackfilledpillardesignusingearthpressuretheory
TheincorporationofRankine’smethodorLog-spiralanalysisintostandardpillardesignhasitslimitations.IntermsofcivilengineeringapplicationsthefunctionalityOfeachofthosemethodshasbeenverifiedthroughexperienceandeachisusedinthedesignofstructures.Sincenoprecedentexistsforearthpressuretheorybeingappliedtothedesignofbackfilledpillarstheusefulnessoftheapproachcannotbecorroborated.Furthermore,theSelf-AdvancingMinertechnologyisnotcurrentlyinusenorareanythincoalseamsbeingextractedinasimilarmanner.
Thepurposeofdevisingamethodofbackfilledpillardesignusingearthpressuretheoryistoseewhatconditionsmaybenecessaryforbackfillingtobepracticaloreconomical.Figure7isaplotofrecoveryrateversusminingdepthbasedonthepaneldimensionsandpillarwidthsofFigure6.Thistypeofplotcanbedevelopedforanysetofthefollowingconditions:
1.Post-peakstrengthofthecoalpillar
2.Frictionangleofcoal
3.Backfilldensity
4.Frictionangleofbackfill
5.Cohesionofbackfill
6.Magnitudeofroofloading
7.Miningdimensions(cutwidth,length,andseamheight).
Thustheimportanceofanyvariablecanbedeterminedintermsofstabilityandoverallrecovery,andaconceptofwhattypeofbackfillmaybenecessarytoachieveacertainrateofrecoverycanbeformulated.Inturn,amoredetailedeconomicanalysiscanbecarriedoutintermsofthecostofbackfillingrequiredtoproduceanadditionaltonofcoal(HumeandSearle,1998;
Donovan,1997;
DonovanandKarfakis,2001).
5Conclusion
Thereislittledoubtthatbackfillhastheabilitytoprovidesupporttosurroundingpillars.However,quantifyingthemagnitudeofthatsupporthasproventobequitedifficult.Earthpressuretheory,commonlyusedinthedesignofcivilengineeringstructures,mayprovideapreliminarytoolforestimatingtheamountofsupportthatbackfillcanprovide.Theadditionalstrengththatbackfillprovidestosurroundingpillarsisimpartedasahorizontalpressurealongthesidesofthepillars.Thisbehaviorofthefillinresponsetolateraldeformationofthepillarsissimilartothatofearth-retainingstructures.Rankine’smethodandthelog-spiralmethodfordeterminingpassiveearthpressurecoefficientscanbeusedtodeterminethemagnitudeoffillsupport.
Theextentofroofcaving,andsubsequentsurchargeloadingofthebackfill,isthemostimportantfactorintermsofthemagnitudeoflateralsupportprovidedbythebackfill.pillarsizesdecreaseandrecoveryincreases.However,thefracturingoftheimmediateroof,anditstime-dependency,isreliantuponlocalgeologicandminingconditions.Thusitisdifficulttopredictandquantifytheextentofroofcaving.Theproposedmethodofbackfilledpillardesignbasedonearthpressuretheorywillremainlimiteduntilamorerigorousmethodforassur-ingroofcaving,anddeterminingthemagnitudeofverticalloading,isdeveloped.
Thepassiveresistanceprovidedbythebackfill,anddeterm
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