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Practice and adaptable conditions classification of aquifer-protective mining in longwall coalface for shallow seam with thin bedrock

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Practice and adaptable conditions classification of aquifer-protective mining in longwall coalface for shallow seam with thin bedrockof,and,minin

    Practice and adaptable conditions classification of aquifer-protective mining in longwall coalface for shallow seam with

    thin bedrock

    JoURNALoFCoALSCIENCE&ENGINEERING

    (CHINA)DOIlO.1007s12404010010l1

    PP1——5Vo1.16No.1Mar.2010

    Practiceandadaptableconditionsclassificationofaquiferprotective

    raininginlongwallcoalfaceforshallowseamwiththinbedrock

    MALiqiang1,ZI

    ZHANGDongsheng.zHAOYongfeng

    (1.SchoolofMines,ChinaUniversityofMining&Technology,Xuzhou221116,China;2.StateKeyLaboratoryofCoal

    Resources&MineSafety,Xuzhou221008,China;3.ShendongMiningBranch,ChinaShenhuaEnergyGroupCo.Ltd.,

    Shenmu719315,China)

    

    TheEditorialOfficeofJournalofCoalScienceandEngineering(China)andSpringer-VerlagBerlinHeidelberg2010

    AbstractAsetofadaptableconditionsclassificationofaquiferprotectivemininginthe

    IongwallcoalfaceforshallowcoaIseamswiththinbedrockwasputforwardtodeaJwith theconflictbetweenwaterprotectionandhighefficiencyfortheminingfieldInwestChina. Thisclassicati0nwassuitableforshallowcoafseamswithdifferentthicknessandwas beneficialtothelocalenvironmentalprotection.Usingthe3-UniversaIDistinctElement Code(3DEC)numericaIsoftware,theheightofthefracturedzonesforshallowcoalseams withthinbedrockwascalculatedandanalyzed,andjtspredictingformulawasachieved.

    Meanwhile.accordingtotheIithologyandtheweatheringdegreeoftheshallowcoaIseam thethicknessoftheprotectivelayerwasdeterminedas10mandtheoverlyingwaterbody ofIoosewatebearingsandforshallowcoaIseamswiththinbedrockwasdividedlnto threetypes,namely,weak,mediumandstrong.Basedonthese,thenecessarybedrock thicknessoftheIongwalIcoalfaceforshallowcoaIseamswiththinbedrockwasconfined accordingtothedifferentminingheightandwateryieldnatureoftheoverlyingIoosewa- ter-bearingsand.Combinedwiththepresentminingstatus,asetofnewmethodsof adaptableconditionsclassificationofaquifer-protectiveminingtechnologyIntheIongwall coalfaceforshallowcoalseamswiththinbedrockwasputforward.

    Keywordsthinbedrock,shallowseam,aquifer-protectivemining,fracturedzone,protec

    tirelayer

    Inthesafeandefficientexploitationofcoalre

    sources,maximizingtheprotectionofwaterresource

    intheoverlyingloosewater-bearingsandremainsa

    typicalproblemintheminingprocessofshallowcoal

    seamsbothathomeandabroadooth,l998;Booth,

    1999;Qianeta1.,2003;Booth,2006).TheShendong

    coolfieldinWestChinaischaracterizedbyshallow

    coalseamswiththinbedrock,whichmakesitpossible

    forpreciouswaterintheoverlyingloosewater-bearing

    sandtobelosttoalargeextentduringtheprocessof

    mining.Whatisworse,thisminingfield,locatedinthe

    MaowusuDesert,ishalfarid,sotheinfluenceofwater

    resourcesontheenvironmentissignificant(Wueta1.,

    2002;Fan2005;?eta1..2006).

    Atpresent,theintermittentlongwallmining

    method,thatis.fullymechanizedcontinuousshort

    wallmining,isgenerallyadoptedtoreducewaterloss.

    However,therecoveryrateofcoa1resourceislowby

    Received:25April2009

SupportedbyNationalNaturalScienceFoundationofChina(50904063);the2007Research

    FundoftheStateKeyLaboratoryofCoalResourcesand MineSafety(07KF09);ScientificResearchFoundationofChinaUniversityofMining&am

    p;Technology(2008A003.2005B002).

    Email:horsema175@163com

    OUIl1ll()r(')liScience&}1]cl'ingfChhm1

    thismeans.Onthebasisofarationa1choiceofthe poweredsupport,theShendongminingfieldisalways tryingtorealizeaquifer-protectiveminingbyadopting themethodofrapidadvancing,combinedwithsec

    tionalmeasures(reducingthesectionalminingheight orfilling).However,alltheseadoptedmethodsarenot systematic.sotheeffectisnotsatisfactoryandsafe productioncannotbeassured(Ye,2003;Wang,2005). Therefore.inthispaper,thepredictiveformulaofthe heightoffracturedzonesaswellastheprotective layerforshallowcoalseamswiththinbedrockwere studiedanddetermined,andtheoverlyingwaterbody ofloosewater-bearingsandwasclassified.Basedon these.thenecessarybedrockthicknessofthelongwal1 coalfacewithdifferentminingheightsforshallowcoal seamswiththinbedrockwasconfined.Combinedwith thepresentminingstatus,flsetofnewmethodsof adaptableconditionsclassificationofaquifer-prot

    ectiveminingforshallowcoalseamswiththinbed. rockwasputforward.

    1i)etenruinationot'fracturedZOlleheight Atpresent,thegenerallyadoptedformulaforthe fracturedzoneheightofalongwallcoalfaceisasfol

    lOWS:

=

    100M/(aM+b)orHe=cM+d,

    where,HEistheheightoffracturedzone,m;isthe miningheight,m;a,b,c,darethecorrespondingpa

    rameters.

    However,theaboveformulaisnotapplicableto shallowcoalseamswiththinbedrock.Accordingto thecomprehensiveconsiderationofthestructuralfea

    turesoftheShendongminingfieldaswellasthein

    fiuenceofhardandsoftcoalstrataonthegrowthof thefracturedzone,theheightofthefracturedzone withdifferentminingheightsforshallowcoalseams withthinbedrockwasanalyzedandcalculatedby usingtheFluid.Mechanicalfunctionofthe3DEC numerica1software.combinedwiththeexperiential datageneralizedfromtheshallowcoa1seammining (Huang,2002;HouandZhang,2005;Maeta1.,2005; Maeta1..2006).Table1showspartiaIcalculation results.

    Table1Heightoffracturedzonecorrespondingto differentminingheights

    Basedontheaboveresults,theformulaofthe heightoffracturedzonesfortheShendongminefield wasachieved:

    =

    10.70+12.64.f11

    Inaddition,theheightofthecavingzonemight becalculatedwithreferencetothe"Standardsofpillar setting&miningunderthesurfaceconstruction.water body,railwayandthemainshafts&entries".Forthe

    sakeofsafety,itshouldberegardedasstrongcover andtheformulais:

    H=100M/(2.1J)l16).(2)

    2Determinationot.theplotectixelayer

    thickness

    Toassurethatwaterinrushdoesnotoccurinthe coalfaceistheprimarytargetofaquifer-protective mining.Theprotectivelayerliesrightabovethefrac. turedzone,whichcanpreventwaterrushingfromthe overlyingwaterbodyofloosewater-beatingsandto thecoalfacethroughthefracturedzone.Thegenerally adoptedminingheightfortheshallowcoalseamisbig, sotheminingheightisusuallydeterminedfrom3.5m tO5.5m.Ifawater-proofcoalpillarissetasstipulated inthe"Standardsofpillarsetting&miningunderthe surfaceconstruction,waterbody,railwayandthemain shafls&entries".theprotectivelayerisabout17.5m to27.5m.fivetimesthethicknessofthemining height,whichisobviouslysohighforthethinbedrock thattherecoveryrateofthecoalresourcewillbere

    stricted.

    Atthesametime,underproperconditions,if thereexistsaclayblanketwiththeminimalthickness ofmorethan3mto5mbetweenthefracturedzone andthewater-bearingsand.thewaterlOSSoftheover. 1yingwater-bearingsandcanbeeffectivelyprevented, whichhasbeenprovedboththeoreticallyandpracti. cally.Astootherwater-proofIayers.suchasmudstone. weatheredrockandsoon,theirthicknesscanbecal

    culatedaccordingtothecorrespondingwater-proof

abilitywiththatoftheabovementionedclayblanket

    (Xu.2005).AbovethebedrockoftheShendongcoal fieldisabeltofweathering.whosemainIithologyis mudstone,siltmudstoneandsiltstone.Basedonthe lithologyanditsweatheringdegreeforshallowcoal seams.combinedwiththeoreticalresearchandindus

    trialtest,itiSconcludedthatthewater_proongability oftheupperbedrockwiththethicknessof4mto10m isidenticalwiththatoftheclayblanketwithathick. nessof3mto5m.Therefore.theprotectivelayerof thelongwal1coalfaceforshallowcoalseamswiththin bedrockcouldbedeterminedas10m.

    \.c'taclicc({udaphlblcc(mdhkmsljl~catiot:(Lli~i.-r-ptcccminh1g_}] 3Theclassificationolloosenwaterbearing sand

    Theregenerallyexistsloosewater-bearingsand abovethetopbedrocksofshallowcoalseamsinthe Shendongcoalfield.Accordingtotheexperiencesof miningunderloosewater-bearingsandindomestic coa1mines.theoverlyingwaterbodyofloosewater- bearingsandforshallowcoalseamswiththinbedrock wasdividedintothreetypes.asshownjnTable2.Itis advisabletoadoptcorrespondingaquifer-protective miningmethodsaccordingtodifferentwaterbodies andcertainminingconditions.

    Table2Classificationofloosewater-bearinglayer 4.Fhenecessarybedrockthicknessoflong

    aIIcoalfacc

    4.1Principlesofbedrockthicknessdetermination

    f11Strongwateryieldnatureoftheloosensand. Whenthewateryieldnatureoftheloosesandis strong,thebedrockmustbethickenoughforadopt

    inglongwallminingmethod.Thatis.thethicknessof thebedrockmustbemorethantheheightofthe fracturedzoneplusthatoftheprotectivelayer.In addition,othermethodssuchasfilling,restrictionof thethickness.aswellasshortwallorstripminingcan alsobeadopted.

    f21Mediumwateryieldnatureoftheloosesand. Itisfoundthatinthecoalfacethedynamicpres

    sureoftheroofismaximalduringthefirstcaveofthe mainroof,sothecoverisdestroyedmaximallytoo andthefractureattheplacewherethecutholeandthe mainroofcavefirstis15%higherthanthatatthe normalextractionprocess.Therefore.whenthewater yieldnatureismedium,theminingmethodsuchas sectionalminingheightreduction.sectionalfillingor sectiona1groutingmaybeusedtoassurethatafter twiceorthreetimesperiodiccavesthestratafractures changefrompre..coalfacetopost..coalfacefromthecut holetotheplacewherethecoalfacecavefirst.Then theminingheightcanbeincreasedgraduallyandfill

    ingorgroutingcanbecanceledbyandby.Therele

    vantincreasedminingheightmaybedeterminedac

    cordingtothefirstcavedistanceandperiodiccave distanceofthecoalface.Thefillingheightshouldbe identicalwiththereducedminingheighttoassurethat thebedrockisthickerthantheflowingfracturezone

andtheprotectivelayer.Afterthefirstcaveandsev

    eralperiodiccavesofthecoalface,thepressureonthe mainroofandthedestructionofthecoverarenotthat greatandthefracturedzoneisl5%lowerthanthatof thecuthole.Basedontheindustrialtestandphysical simulation.itisfoundthatthefracturedzonewill closegraduallybehindthecoalfaceandthenthede

    stroyedcovercanstillbewaterproof.

    f31Wleakwateryieldnatureoftheloosesand. Theloosewater-bearingsandoftheShendong coalfieldvariesgreatly,sothesidestreamsarenot undergoodconditions.Tominemaximally,thefrac. turedzonemaybeallowedtoentertheloosesand whenitswateryieldnatureisweak.whichistherain

    ingmethodofsettingsandproofcoalpillars.Byal

    lowingtheminorfracturedzoneintothewaterbearing sand,thisminingmethodcanensurecomparatively successfulsand.proofresultandwaterprotectionel'- fectbecauseoftheintactbedrockandtheweakwater yieldnature.Thefracturedzonewil1graduallyclose andthegroundwaterlevelwillrecoverbyandbybe

    hindthecoalface.

    4.2Necessarybedrockthicknessforlongwallcoa- Ifacemining

    Torealizeaquifer-protectivemining,theneces

    sarybedrockthicknessofthelongwallcoalfacewim difrerentminingheightisconfinedaccordingtothe correspondingdifferentwateryieldnatureoftheloose water-bearingsand.asshownin11able3.

    5Adaptableconditionsclassificationofaq-

uiferprotectivemining

    Giventhegeologicalminingconditionsofthe Shendongcoalfield.itswaterbodyprotectedandthe presentminingstatus,asetofnewmethodsofadapt

    ableconditionsclassificationofaquifer-protective miningtechnologywasputforwardaccordingtothe differentbedrockthickness.asshowninTable4. f11Whentheheightofthebedrockismorethan 95m,thenormallongwallminingmethodcanbe adopted.Thepresentmaximalminingheightoffully mechanizedminingequipmentis5.5m.andthe maximalheightofthefracturedzoneshouldbe71m accordingtoFormula(1),plustheprotectivelayer thicknessOf20m.theheightofthewaterproofbed

    rockiscalculatedtobe91m.theintegerbeing95. Therefore,the95mbedrockcanrealizethecomplete miningof5.5mcoalseamforonce.

    0[111]~11(,l,LL]lJIc1]cc&ll1'1ccring((hina) Table3Thenecessarythicknessofbedrockcorrespondingdifferentminingheightofrealizin

    gaquifer-protectivemining

    m

    Table4Classificationofaquifer-protectiveminingtechnologyoflongwallcoalfaceforshall

    owseamswiththinbedrock

    r2,WhentheheightofthebedrockiSlessthan 35m.forprotectingwaterresource,itshouldnotbe minedatthemoment.

    r31WhentheheightofthebedrockiSinthe50

    100mrange,longwallminingcanbeused,bychoos

    ingtheappropriateheightaccordingto11able2.When thelooselayerofthemiddleaquifercanbetakenlO

    callytoreduceminingheight,partialfilling,partial groutingandothermeasurescanbeused.However, whentheminingheightiSsmal1.shortwallmining

    shouldbeadopted.Shortwallminingandstripmining preventtherooffromfalling,butrestrictsthedevel

    opmentofwaterchannelstoachievethepurposeof waterprotection.ThekeyiStodeterminethereason. ablecollapseheight.

    6IndUSII'ialtest

    6.1Thegeologicalminingconditions

    ThecoalseamiS1withtheaveragethicknessof about5.8mandthetiltingangleofthecoalseamisl

    5..whichiSminedinthe51201coalfaceofthe ShangwanCoalMine.XishaDitchgoesthroughthe groundofthecoalfaceTheoverlyingbedrockthick

    ness0fthe1coalisbout45mto60mandthethick

    nessoftheloosewater-bearingsandiSabout10m. whosewateryieldnatureismedium.

    Threepeepholesandonewater1evelobservation holeweresetinthisarea.NeartheNO.2peephole,the thicknessoftheloosesandiS7.70m.andthatofthe bedrockiS48.75m.NeartheNo.3peephole.the \1.\liqiangctl1Iracticcandadaptableconditionsclassilicalionofaqtfiler

    protecti\t2minin~in

    thicknessoftheloosesandis7.70m.andthatofthe bedrockis47.95m.

    6.2Possibilityofaquifer-protectivemining Thebedrockatthetopoftheareatakesintoac. countthenearly5mofweatheredrock,thusthepro

    tectivelayerthicknessshouldbesetat10m.Evenso.

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