Influence of longwall gateroad convergence on the process of mine ventilation network-model tests

InternationalJournalofMiningScienceandTechnology29(2019)585–590ContentslistsavailableatScienceDirect

InternationalJournalofMiningScienceandTechnologyjournalhomepage:www.elsevier.com/locate/ijmstIn?uenceoflongwallgateroadconvergenceontheprocessofmineventilationnetwork-modeltests

AndrzejWalenteka,TomaszJanoszeka,?,Stanis?awPrusekb,AleksanderWranaaabDepartmentofExtractionTechnologies,RockburstandMiningSupport,CentralMiningInstitute,40-166Katowice,PolandCentralMiningInstitute,40-166Katowice,Polandarticleinfoabstract

Hardcoalminesarerequiredtoconstantlyventilatemineworkingstoensurethattheaircompositionisatacertainhumidityandtemperaturelevelthatiscomfortableforundergroundmineworkers,especiallyindeepdeposits.Allundergroundworkings,whicharepartofthemineventilationnetwork,shouldbeventilatedinawaythatallowsmaintainingproperoxygenconcentrationnotlowerthan19%(byvol-ume),andlimitsconcentrationofgasesintheairsuchasmethane,carbonmonoxideorcarbondioxide.Theair?owinthemineventilationnetworkmaybedisturbedduetothenaturalconvergence(deforma-tion)andleadtochangeinitsoriginalcross-section.Reducingthecross-sectionalareaoftheminingexcavationcauseslocalresistancesintheair?owandchangesinaerodynamicpotentials,whichleadstoemergencystatesinthemineventilationnetwork.Thispaperpresentstheresultsofnumericalsimu-lationsofthein?uenceofgateroadconvergenceontheventilationprocessofaselectedpartofthemineventilationnetwork.Thegateroadconvergencewasmodelledwiththe?niteelementsoftwarePHASE2.Thein?uenceofchangesinthecross-sectionalareaofthegateroadontheventilationprocesswascarriedoutusingthecomputational?uiddynamicssoftwareAnsys-Fluent.ó2019PublishedbyElsevierB.V.onbehalfofChinaUniversityofMining&Technology.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).Articlehistory:Received12September2018Receivedinrevisedform10December2018Accepted16January2019Availableonline26June2019Keywords:GeomechanicsConvergenceNumericalmodellingVentilationprocessSupport1.IntroductionThecross-sectionofalongwallgateroadcouldhaveanimpactonthesafetyofthetransportationprocesstothelongwallregionsandensuringtheirventilationcapacity.Theissueofcross-sectionalareaofthelongwallgateroadisinextricablylinkedtothelevelofmethanehazardintheareaofexploitation.Prusekstudiedthechangesofcross-sectionsoflongwallfacesbeforeandbehindthefrontofthelongwallsandcomparedin-situmeasurementswiththeforecastedresultsdeterminedhighusefulnessofthedevelopedforecastingmethodsinordertoreducethemethanehazard[1].Luetal.studiedmethaneanddust?owinundergroundmines,usingacomputational?uiddynamics(CFD)inordertodemonstratethecontinuousminer’sadverseaffectsontheair?owandmethaneanddustconcentrations[2].Theissueoflongwallcross-sectionisassociatedwithlongwallventilationmethodsused[1].Thedom-inantmethodsoflongwallventilationare:(1)‘‘U”alongsolidcoal,about70%oftheexploitedlongwalls,and(2)‘‘Y”or‘‘invertedY”,about25%oftheexploitedlongwalls.Inthelightoftheabove,maintainingappropriatedimensionsofthecross-sectionoflongwallgateroads,inbothmethodsofventi-?Correspondingauthor.E-mailaddress:tjanoszek@gig.eu(T.Janoszek).lationisimportantasitaffectstheconditionsofsafelongwalloperation[3,4].Theissueofmaintainingproperdimensionsofmaingatesaheadofthelongwallfrontwhentheyareventilatedon‘‘U”alongsolidcoalaffectstheventilationcapacity,andthisinturnaffectsthevalueofthecalculatedcriterialmethanebearingcapacity.Oneshouldmentiontheformationofmethanehazardinthecaseofachangeinthecross-sectionofminingexcavationsintheareacoveredbyminingexploitation.Intheproductionregion,thechangeinthecross-sectionofmineworkingslongwall-air-headingsandtheresultingpotentialdifferenceisshapedbythestreamofmethaneemittedfromthegoafalongsolidcoal(Fig.1).BasedonFig.1,itcanbeconcludedthat:(a)reducingthecross-sectionofthegateroadsupplyingairtothelongwallincreasesthevelocityofair?owalongthelongwallworking,whichincreasestheairescapethroughthegoaf;(b)increasingtheradiusR1toR2asaresultoftighteningthelongwallgateroadinthegoafcontributestoextendingthedurationofself-ignition,thusspontaneous?reshaz-ard;(c)increasingtheradiusfromR1toR2increasesthemigrationofmethanedesorbingfromthesurfaceareaofR2tolongwallworking;and(d)increasingtheradiusfromR1toR2reducestheef?ciencyofmethanedrainage.Thereductioninthedimensionsofgateroadsleadstoanincreaseinthedifferenceinaerodynamicpotentialsbetweenthehttps://doi.org/10.1016/j.ijmst.2019.06.0132095-2686/ó2019PublishedbyElsevierB.V.onbehalfofChinaUniversityofMining&Technology.ThisisanopenaccessarticleundertheCCBY-NC-NDlicense(http://creativecommons.org/licenses/by-nc-nd/4.0/).586A.Walenteketal./InternationalJournalofMiningScienceandTechnology29(2019)585–590Fig.1.Schematicofalongwallventilationon‘‘U”goafandtheconvergedgateroads,whichleadstoanincreaseinthe?owrateofthegasmixturewithmethanefromgoaftothelong-wallworkinganddependson:theratioofchanginglongwall-gateroadcross-section;the?owrateofairthroughthelongwall;andtheaerodynamicresistanceatlengthoftheconvergedgateroads.Shookstudiedthein?uenceofconvergenceofroofand?oorinundergroundmineopeningsonreductionoftheeffectivenessofthemineventilationsystem,whichisessentialforthedilutionofmethanegasandairbornerespirabledust[5].Caoetal.studiedthestabilityofdeeproadwaysinanundergroundmine,undertheconditionofextremelyfracturedsurroundingrockstrata,inordertodetermineitseffectongateroadsdeformationandmain-tainthelong-termstabilityoftheroadway[6].Jiangetal.simu-latedtheeffectoffracture-inducedweakeningofrockmassongateroadstability[7].Prusekstudiedtheconvergenceprocessofgateroadsandpresenteddifferentmethodsallowingtheirpredic-tioninordertolimitthechangeofreinforcementofsupportorincreaseinworkingcross-sectionalarea[8,9].Rotkegelstudiedthein?uenceofthegeometryofportalsupportofworkingT-junctionsonitsstressstateinordertoreducegateroadconver-gencetakingintoaccountitsoptimization[10].Rotkegeletal.studiedin?uenceofspeci?cloadsintermsofresistanceparame-ters,convergenceandworkoftheroadwaysupports[11].Takingtheaboveintoaccount,itcanbestatedthatatthestageoflongwallplanning,itisimportanttomakeapredictionoflong-wallgateroadsconvergence,whichwillin?uencethewaysoflong-wallventilationon‘‘U”,‘‘Y”orothersystemdesign.2.NumericalmodelTheobjectofmodelresearchisalongwallinthecoalseamatadepthfrom995to1040mwithaninclinationofabout6°to16°andathicknessofupto2.6m.Intheroofstrata,thereisshalelocallypassingintoasandyshalewithathicknessfrom0.2to1.3m,overwhichthereissandstone.The?oorisformedbyshale,locallysandstone.TheschemeoftheanalysedlongwallpanelisshowninFig.2.Theanalyzedlongwallisventilatedon‘‘U”systembymeansofgateroad‘‘A”withacross-sectionof17.9m2,whichconnectstoalongwallworkingwithacross-sectionof9.2m2.Theairconsumedfromthelongwallworkingisdischargedtotheventilationnetworkoftheminewiththe‘‘B”gateroadwithacross-sectionof14.7m2.At10,50and100mfromthelongwallface,thein?uenceoftheconductedextractionwiththerooffallontheconvergenceofgate-roadswassimulatednumerically.Modellingoftheconvergenceprocessoftheundergroundgate-roadswascarriedoutusingthe?niteelementmethodinthepro-gramPHASE2.Themodellingprocessofthegateroadscross-sectionalareaimpactontheprocessofventilationwassimulatedusingtheComputationalFluidDynamics(CFD)methodwithuseofAnsys-Fluentprogram.Theresultsofthemodeltestsoflongwallgateroadsdeformationhaveanin?uenceontheselectionofpow-eredsupportintermsofensuringtherequiredsupportstabilityintheareaofthelongwallT-junctionsupportaswellasventilationprocess,especiallyinthepresenceofsoft?oorrocks[12,13].Fig.2.Analyzedpartofthemineventilationnetwork.2.1.NumericalsimulationofgateroadsconvergenceThenumericalcalculationsofgateroadAandgateroadBcon-vergenceintheconditionsofthemovinglongwallfacewereper-formedontwonumericalmodelsdesignedintheformofashield70mwideand70mhigh(Fig.3).Theangleofinclinationofthegoaflineinthecomputationalmodelwasadoptedat70°,whiletheheightofthegoafcorrespondsto?vetimesthethicknessoftheseam[8,9,14,15].ThemechanicalpropertiesofthegoafwereadoptedinaccordancewiththepaperandpresentedinTable1[16].ThegateroadAsupportis?P9/V32/4/Atype,whereasgateroadBsupportis?P10/V32/4/Atype,whichinbothcasesarebuiltinaspacingof0.8m.Thesupportgeometrywasinterpretedasabeam,towhichV29pro?leparameterswereassigned[10,17].Inaddition,thefollowingassumptionsweremadeforthepre-sentedmodel:modelledrockmassisanelastic–plasticandisotro-picmedium,nopossibilityofhorizontaldisplacementatthemodelverticalboundaries,nopossibilityofverticaldisplacementatthemodelhorizontalboundaries,?eldstressesresultduetodepthof1000mandtheaveragevolumeweightoftheoverburden,andduetothein?uenceofpreviousextractionlocatedabovetheseam,themodelloaddistributionvaluewasincreasedbyanadditional20%[14].Therockmassisisotropicandelastic-plastic.ThelimitstateconditioncalculatedaccordingtotheHoek-Browncriterionforthefracturedrockmasswasde?nedasEq.(1)[18]:r0?r0tr0ciemr3brcitsTae1Twherer’1andr’3aretheeffectivemaximumandminimumbreak-ingstress,MPa;mb,sandaaretheparametersfortheHoek-Browncriterion;andrcithecompressiveuniaxialstrengthoftherocksam-ple,MPa.Parametersmb,aandsaredeterminedfromthefollowingdependencies[18].??máexpGSIà100??b?mi28à14De2Twheremiistheconstantforintactrockdependingonitstype,determinedonthebasisoftriaxialcompressiontest;GSIthegeolog-icalstrengthindex;andDthecoef?cientofdestructiondependsonthetypeofrocksandthemethodofextraction.Thefundamentalvaluesofrockmassparameters,includingtheHoek-BrowncriterionaresummarizedinTable1.TheassumptionspresentedaboveallowedforthecalculationofgateroadAandBdeformationssubjectedtothein?uenceofoper-atingpressure.Theobtainednumericalmodellingresultsarepre-sentedintheformofdisplacementcontoursoftherockmassA.Walenteketal./InternationalJournalofMiningScienceandTechnology29(2019)585–590587Fig.3.Finiteelementmodel.Table1

Rockmassparametersadoptedinnumericalmodelling.TypeofrockCoalClayslateSandstoneGoafYoung’smodulusE(MPa)145621395803400Poisson’sratio0.300.250.210.40CompressivestrengthRc(MPa)10.726.057.02.0Parametermb0.71191.0092.5140.500Parameters0.00080.00300.00600.0001aroundtheanalysedgateroadsatadistanceof100,50,10mfromthelongwallfaceandatthelongwallface(Figs.4and5).Inaddi-tion,Table2reportsthepredictedvaluesofverticalandhorizontaldeformations.Thecross-sectionalareaofthegateroadsintheabove-mentioneddistancesfromthelongwallfaceweredetermined.AnalysingtheresultsofconvergencepredictionforgateroadAandgateroadBsummarizedinTable2,itcanbeconcludedthatthehighestvaluesofverticalconvergenceintheareaofT-junctionare1460and1235mm,whilethehorizontalconvergenceamountsto900and1005mm,respectively.Both,inthegateroadAandBthephenomenonof?oordeformationdominateswhichcon-stitutesover80%ofthevalueofverticalconvergence.Onthebasisoftheobtainedvaluesofpredictedvaluesofgateroadsconver-gence,theircross-sectionformedasaresultofrockmassdeforma-tionwasdetermined.InthecaseofthegateroadAis9.2m2,whileforgateroadBis7.7m2.Referringthepredictedvaluestotheinitialvaluesofgateroads,areductioninthecross-sectionbyapproxi-mately48%wasobtained.2.2.NumericalsimulationoftheventilationprocessThesimulationoftheair?owprocessinthemineventilationnetwork,basedontheCFDmethod,requiresde?ningthegeometryofmineworkingsnetworkintheformofaspatialmodel.Knowl-edgeofparameterssuchasthelengthofgateroadsandtheshapesoftheircross-sectionsisimportant.Itisoptimaltousedrawingsofgateroadscross-sectioninCADformatusingappropriatecomputerprograms.Itisimportanttocarryoutpreliminarysimulationsbeforeproceedingtothepropercourseofcalculations,whichwillenabletoevaluatethecorrectnessofthedevelopednetworkofexcavations.ItisrecommendedtocarryoutcalculationsforFig.4.ConvergenceofgateroadAatfourdifferentdistances.Fig.5.ConvergenceofgateroadBatfourdifferentdistances.