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

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

《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》由会员分享，可在线阅读，更多相关《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（11页珍藏版）》请在冰豆网上搜索。

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