许疃煤矿1.2Mt-a新井设计-离层分区注浆减沉技术在许疃煤矿应用探讨

本科生毕业设计（论文）题目：许疃煤矿1.2Mt/a新井设计离层分区注浆减沉技术在许疃煤矿应用探讨本科生毕业设计学院：矿业工程专业：采矿工程设计题目：许疃煤矿1.2Mt/a新井设计专题：离层分区注浆减沉技术在许疃煤矿应用探讨毕业论文题目：许疃煤矿1.2Mt/a新井设计毕业论文专题题目：离层分区注浆减沉技术在许疃煤矿应用探讨毕业论文主要内容和要求：根据采矿工程专业毕业设计大纲，本毕业设计分为一般部分、专题部分和翻译部分，具体包括：1、一般部分：许疃煤矿1.2Mt/a新井设计，主要内容包括：矿井概况、矿井工作制度及设计生产能力、井田开拓、首采区设计、采煤方法、矿井通风系统、矿井运输提升等。2、专题部分：离层分区注浆减沉技术在许疃煤矿应用探讨。3、翻译部分：完成近3-5年国外期刊上与采矿或煤矿安全有关的科技论文翻译一篇，要求不少于3000字符。大学毕业论文答辩及综合成绩答辩情况提出问题回答问题答辩委员会评语及建议成绩：答辩委员会主任签字：年月日学院领导小组综合评定成绩：学院领导小组负责人：年月日

摘要本设计包括三个部分：一般部分、专题部分和翻译部分。一般部分为许疃煤矿1.2Mt/a新井设计。许疃煤矿位于安徽省宿州市，地处平原，土地肥沃，农作物生长良好。井田南北走向长6.27~6.47km，东西倾向宽3.11~3.73km，井田面积约19.94km2。井田内主要可采煤层72煤层，倾角6.6~15.5°，平均厚度3m。矿井工业储量为123.56Mt，可采储量为85.74MtMt，设计服务年限54.9a。矿井正常涌水量为1050m3/h，最大涌水量为1660m3/h。矿井相对瓦斯涌出量为22m3/t，最大绝对瓦斯涌出量为64.83m3/min，属高瓦斯矿井。煤层属可能自然发火煤层，煤尘有爆炸危险性。根据矿区及井田地质条件，设计采用立井单水平开拓方式。上山布置带区，断层上盘布置采区，全井田共划分为四个带区，一个两翼采区，一个单翼采区。轨道大巷、胶带机大巷和回风大巷根据服务年限布置在煤层或岩层。本矿井为高瓦斯矿井，设置专用回风井巷，并预掘底板瓦斯抽排巷进行瓦斯卸压抽放，矿井通风方式采用中央并列式。针对涌水量大，大巷均向井底车场微斜自然排水，下山上行开采，后期向采空区排水。首采区带区式准备，工作面设计长度220m，采用综合机械化采煤工艺。矿井年工作日为330d，昼夜净提升时间为18h。矿井采用“四六”制工作制度，三班生产，一班检修。生产班每班完成2个采煤循环。循环进尺为0.8m，日产量为4243.54t。矿井煤炭采用胶带输送机运输，辅助运输采用DLZ110F柴油机单轨吊。主井采用一对12t底卸式箕斗提煤，副井采用多绳摩擦式提升机提升一窄（1.02）一宽（1.67）罐笼。专题部分题目为：离层分区注浆减沉技术在许疃煤矿应用探讨。在绿色开采及科学采矿理念的指导下，结合许疃煤矿覆岩特征及“三下”压煤状况，提出对高采出率下减缓地表下沉技术的探索。运用数值模拟方法对离层区注浆减沉技术在许疃煤矿的使用进行了分析探讨。设计工作面长160m，关键层下岩层可达超充分采动状态；离层区充填体分担了部分覆岩载荷，分区煤柱应力集中明显减小；分区间跳采，因跳采出现的孤岛工作面待两侧离层区充填稳定后仍用离层区充填方法开采，数值模拟结果表明此方法可以有效减缓地表沉陷、提高资源开采率。翻译部分主要讲述了爆破卸压的应用现状，包括地质、岩石性质、开采条件和爆破参数（炮孔布置、孔深、爆破载荷等），讨论了爆破卸压的优势并对其作为解决高采动应力引起冲击矿压的效果进行了评价，英文题目为：DestressBlastinginCoalMining–State-of-the-ArtReview。关键词：许疃煤矿；立井单水平；瓦斯卸压抽放；下山上行开采；单轨吊；F5逆断层；变频对旋式通风机；离层区；数值模拟；爆破卸压 ABSTRACTThisdesignincludesthreeparts:thegeneraldesign,themonographicstudyandthetranslation.Thegeneraldesignisabouta1.2Mt/anewundergroundminedesignofXutuanCoalMine.XutuanCoalMineliesinSuzhouCity,Anhuiprovince，wheresoilisflatandfertile.It’sabout6.27~6.47kmonthestrikeand3.11~3.73kmonthedip,withthe19.94km2totalarea.Themainaquifercoalseamis72coalseamwithanaveragethicknessof3m,andthedipis6.6~15.5°.Theprovedreservesofthiscoalmineare123.56Mtandtheminablereservesare85.74Mt,withaminelifeof54.9years.Thenormalmineinflowis1050m3/handthemaximummineinflowis1660m3/h.Theminerelativegasemissionquantityis22m3/t,andtheabsolutegasemissionquantityis64.83m3/min.Thecoalseamisfeasiblespontaneouscombustioncoalseamandthecoaldusthasexplosionhazard.Basedonthegeologicalconditionofthemine,thisdesignusesaverticalshaftsingle-leveldevelopmentmethod,whichdividedintofourbandsandtwodistricts,andtrackroadway,beltconveyorroadwayandreturnairwayaredifferentondifferentlifetime,arrangedinthefloorrockorcoalseam.Takingintoaccountofthehighgasemission,setupdedicatedroadwayforventilation,andexcavesbottomgasdrainageroadwaytoreliefgaspressure,mineventilationmethoduseCentralabreastventilation.inconnectionofbigwaterinflow,roadwaytiltstotheshaftbottomtofacilitatedrainage,ascendingminingisadoptedinthedistrictdip,takeadvantageofgoaffordrainage.Designedfirstminingdistrictmakesuseofthemethodofthestripdistrictpreparation.Thedesignlengthofworkingfaceis220m,whichusesfullymechanizedminingtechnology.Theworkingdaysinoneyearare330.Everydayittakes18hoursinliftingthecoal.Theoperationmodeinthemineis“four-six”withthreeteamsminingandtheotheroverhauling.Everyminingteammakestwoworkingcycle.Soeverydaythereare6workingcycles.Theadvanceofaworkingcycleis0.8m,andthequantityof4243.54toncoalismakedeveryday.Mainroadwaymakesuseofbeltconveyortotransportcoalresource,andoverheadmonorailtobeassistanttransport.Themainshaftusesadouble12tskipstoliftcoalandtheauxiliaryshaftusestwocage，oneis1.02mandtheotheris1.67m.Themonographicstudyentitled“ApplicationofisolatedsectiongroutingtechnologyforoverburdenbedseparationspaceinXutuancoalmine”.Undertheguidanceofconceptofgreenminingandscientificmining,inconnctionofcharacteristicofXutuan,exploringawaytoreducesubsidencewithahighrecovery.Studidbynumericalsimulation.Thelengthofwokingfaceis160m,rockstatumunderthekeystatumcanbefullmining;intermsofbackfillsharessomestress,coalpillarstresswassignificantlyreduced.skip-miningamoneisolatedsection,islandminingfacewasminedafterstabilityofbothsidesofgob.Thenumericalresultsshowthatthismethodcaneffectivelyreduceminingsubsidence,increasethecoalrecovery.Thetranslatedacademicpaperpresentsastate-of-the-artreviewofdestressblastingincoalmining.Informationsuchasgeology,rockproperties,miningconditionsaswellasblastingparameterssuchasblastholelayout,holelength,explosiveloadingetc.arepresented.Thepaperdiscussesthemainbenefitsofdestressblastingandtheevaluationofitseffectivenessasameasuretoovercomethechallengesofhighmining-inducedstressescausingcoalbumpsandrockbursts.Thetitleis“DestressBlastinginCoalMining–State-of-the-ArtReview”.Keywords:Xutuancoalmine;shaftsingle-leveldevelopment;gasdrainageandreliefgaspressure;ascendingmininginthedistrictdip;overheadmonorail;F5reversefault;rotatingfanwithfrequenceconvision;overburdenbedseparationspace;numericalsimulation;DestressBlasting

目录一般部分1矿区概况与井田地质特征 页英文原文DestressBlastinginCoalMining–State-of-the-ArtReviewPetrKonicek1,*,ManiRamSaharan2,HaniMitri31InstituteofGeonicsAcademyofSciencesoftheCzechRepublic,Studentska1768,70800Ostrava-Poruba,CzechRepublic,2CentralInstituteofMining&FuelResearch(CIMFR),SeminaryHills,Nagpur,India,3McGillUniversity,Montreal,Quebec,CanadaH3A2A7Abstract:Coalmineworkingscontinuetofacethechallengesofcoalbumpsandrockburstscausedbyhighmining-inducedstressesduetohighoverburdenpressuresassociatedwiththeextractionofbrittle,lowstrengthcoalseams.Despiteofthefactthatdestressblastinghasbeenappliedforalmostacentury,itisstillnotapopularchoice.Thispaperpresentsastate-of-the-artreviewofdestressblastingincoalmining.Informationsuchasgeology,rockproperties,miningconditionsaswellasblastingparameterssuchasblastholelayout,holelength,explosiveloadingetc.arepresented.Thepaperdiscussesthemainbenefitsofdestressblastingandtheevaluationofitseffectivenessasameasuretoovercomethechallengesofhighmining-inducedstressescausingcoalbumpsandrockbursts.Keywords:Mining,Coal,DestressBlasting1.IntroductionItiselementarybutimportanttoillustratethatanundergroundexcavationinitiatesaprocessofreequilibrium,whichleadstothegenerationofstressesaroundtheexcavationinamannerthatfreesurfacesbecomeplanesforprincipalstressesandexperienceabi-axialstateofstresscondition.Theexcavationboundariesmayexperiencedamageeffectsduetostressesandtheseeffectsforcoalminescanbedislocationofrockreinforcement,interbedcrossoveroflaminatedroofrockmass,cutterfailure,floorheaveand/orrockburst/coalbump(Fig1).Thesedamagingeffectsarepresentedintheorderoftheirseverityaccordingtothestresslevel,correspondingstrength(uniaxialandpoly-axial)atthepointofconsiderationofthestressloading.Excessofthestresslevelincomparisontothestrengthandtherateatwhichtheexcessisattainedduringthere-equilibriumprocessismanifestedintothedifferentdamagingeffectsasillustratedinFigure1.Afasterrateinobtainingexcessstresseswillresultintorockburst/coalbump.Occurrenceofthisexcessstressoveragreaterareawillincreasetheseverityofthedamagingeffects.Further,partoftheexcavationexperiencesstressconcentrationandanotherexperiencesstressrelaxationduetotheshapeoftheopeningandinsitustressdirections.abcdFig1.(a)RockboltdislocationinanIndiancoalmine;(b)InterbedcrossoverinacoalmineofSouthAfrica[1];(c)CutterrooffailureinanUScoalmine[2];(d)RockburstinaGermancoalmine[3].Pastresearchformeasurementofstresses,understandingofstressesandpredictionofthetimingwhenandtherateatwhichthestresseswillbeinexcessofthestrengthhasbeenamixedsuccess.Theminingprocesshas,inthemeantime,becomefaster,largerandbeingdoneatdeeperlevels.Itisthusnecessarythatprotectivemeasuresbeevolvedtodealwiththedamagingeffectsofexcessivestresses.Figure2illustratesdifferentmethodsevolvedtodealwiththedamagingeffectsofexcessivestressesanddistressblastingisoneoftheoldestandproactivemeasuresamongsttheothermethods[4].Themechanismofdestressblastingisnotwellunderstooddespiteoftheapplicationofdestressblastinginawiderangeofminingconditionsandobjectives.Thepaperpresentsvariousconditionsforwhichdestressblastingisappliedfordeepcoalminesanddiscussesthepossibilitiestofurtherimprovethemethod.Theapplicationofdestressblastingisaimedintothezonesofstressconcentrationinsuchamannerthatthestressconcentrationzoneshiftedinteriortotherockmassthusleavingaprotectivebarrierbetweentheworkforceandthestressconcentrationzone.ThismechanismofdestressblastingisillustratedinFigure3,whichdemonstratethatdestressblastingshiftsstressconcentrationzoneawayfromtheactiveworkingfront.Fig.2.Methodstoreducedamagingeffectsofexcessivestresses[4]Fig.3.Geomechanicseffectsofdestressblasting[5]2.NaturalandminingconditionsHardcoaldepositsaremostlycomplexsedimentarysequencescontainingcoalseams(multiseamdeposits)inUpperPaleozoicage.Rocksbetweencoalseamscompriseshale,mudstones,siltstones,sandstonesandconglomerates.Thicknessofcoalbearingstratarangesfromhundredstothousandsofmeters,whereasthethicknessofcoalseamsvariesfrom1totensofmeters.Thefeaturemostcommonwherecutterrooffailureorfloorheaveoccursisthepresenceofthinlylaminatedroof/floor.Thefeaturemostcommontoseamsinwhichrockburstoccuristhecloseproximitytoastrong,thickandrigidstratum[3].Thesestrataconsistofsandstonesandconglomeratesinmostcoalfieldsandinrarecasestheyconsistofothertypesofgeologicalmaterialsandcanbedefinedascompetentmassiveelasticrock[6].TypicalexamplesofrockburstpronestrataaredescribedinFig4.SummaryofthebasicrockpropertiesofcarboniferousrocksisillustratedthroughTable1[3,7].Itisalsoimportanttounderstandthatcoalbearingstratahaveverydifficultstructuraltectonicpattern[14]withverycomplicatednaturalstressfieldandcombinationofthesecausesstressdamages[7,8,9,10].Fig.4.Typicalpropertiesofcarboniferousrockmasswithcompetentrocklayers(A)LazyColliery(theCzechpartofUSCB);(B)Germany[11];(C)ChinakuriColliery(India)[12]Table1.Rockproperties*RockUCS[MPa]RQD[%]Bedthickness[m](competentrocks)Coal10–30--Mudstones35–65--Siltstones40–15060–905–10Sandstones50–17060–9010–100Conglomerates40–14060–905–20*GeneralizeddatafromCzech,German,Indian,Polish,UkraineandUSACollieries[3,7,11,52]Miningconditionsinfluencetherockmassresponseandstressconcentration.Someoftheseconditionsarelistedbelow.•miningwithinmorethanonecoalseamsseparatedtoeachotherby3mtoabout100m,•extractionthicknessandsizeoftheopenings,•protective/unminedpillarsincoalseams,•partunminedoverlyingseams,•advancerateofmining,•differentadvancedirectioninoverlyingseams,and•improperlysuperimposedmininglayoutsinmulti-seamminingTypicalexampleofcomplicatedmininghistoryispresentedinFig.5,whichwaspublishedbyDvorskyetal.[47].Figure5representstimesequenceofmininginareaof4thminingblockinCSACollieryintheCzechpartoftheUpperSilesianCoalBasin(USCB).TheschemeofmininginthelevelofseamNo.530whichwasminedwithmanyoverlyingseamsindifferentdirections(Fig.5showsonlyfourofthem)isillustrated.Overlyingseamshadmanyunminedpillarsthatwereleftinthecentralpartoftheminingblockduetoatectonicfaultoccurrence.Theminingconditionswerefurthercompoundedduetochangingofminingdirectioninwestandeastpartofminingblock.ThiscomplicatedminingsituationtogetherwithverydifficultnaturalconditionscausedmanyrockburstwhileminingtheseamNo.530[47,15].Fig.5.Schematicmapoftimesequenceofminingofparticularlongwallsinareaof4thminingblock(seamNo530)ofCSACollieryintheCzechpartoftheUSCB;adjustedafter[47].Numerousminingcasestudiesofexcessivedamagesfrominducedstressescanbepresentedfrommanyminingregionsacrosscontinents,suchasAustralia[16],CzechRepublic[,15,17,18,47],Germany[3,11,19,20],Poland[21,22,23,37],USA[24],China[25,26]andIndia[27].3.DestressblastingasproactivemeasureDestressblastingincoalseamsorimmediateroofandfloorrockmasshasbeenadoptedtomanagecutterrooffailure,floorheaveandrockburst/coalbump.Theobjectivehasbeentoshiftexcessiveinducedstressestotheinteriorrockmassandtoprovideaprotectivebarriersurroundingtheexcavation.Threetypicalconditions,forwhichdestressblastinghasbeenadopted,areillustratedinFigure6.Theseusedestressblastingtoavoidcutterrooffailure,floorheaveandrockburst.MajorprincipalstressforthecasesshowninFigure6ishorizontalexceptforthecaseoflongwallminingwheremajorprincipalstressfromverticaldirectionisthecauseofconcern.Thesecasestypicallyusefarthestonethirdlengthoftheboreholechargedwithpermittedexplosive(singlecartridgepermetreofthechargelength)andboreholelengthdesignedsuchthattheexplosivecolumnbeginsatleast3mor1.5timestheexcavationheightfromtheboreholecollar[3].Theconditionunderwhichdestressblastingisrequiredandthelocationofdestressblastingisdeterminedfromdrillingrateandnoiseoftestdrillholes.Theeffectivenessofdistressblastingismeasuredfromchangeinsupportpressureandrateofconvergenceofroof/floorrockmass.Successfulapplicationofdestressblastingundersuchconditionsrequiresthatitshallbepracticedonregularbasisandbeapartofroutineminingcycle.Kexin[25]andXiaetal.[26]describeapplicationofdestressblastingtocontrolfloorheavefordeepcoalminesinChina.ThedestressblastinginvolveapatternandobjectiveconsistentTable2–parametersofboreholepatternfordestressblastinginthetestgallery[25]LayoutBoreholeChargingTestsectionpatternRowspacing,mToespacing,mColumnspacing,mSpacing,mDepth,mOrient-ationCharging,mMudstemming,m12row,3holeinflowerpattern4.7┴towallLeft1.6Left3.1Right1.9Right3.822deephole,1shallowholeDeephole4.2Deephole1.5Deephole2.7Shallowhole3.2Shallowhole0.7Shallowhole2.532row3holeinflowerpattern4.10.9-1.83.2-2.342linerow4.30.4-1.23.9-3.1withtheFigure6(b).DetailsofthepatternreportedbyKexin[25]isgiveninTable2.Thedestressblastingprogramreportedtobeasuccessinthemine.(a)Systemofdestressblastingtolimitcutterrooffailure(b)Systemofdestressblastingtolimitfloorheave(c)SystemofdestressblastingtolimitrockburstingatedrivingandlongwallminingFig.6.DestressblastingasproactivemeasurefordifferentobjectivesDestresscoalblastingissimilarlyusedtoalleviaterockburstsproblemsinPolishandCzechCollieriesbutalsoinGermancollieriesinthepast[18,19,28,29,30,31,32,33].Atypicaldestressblastingpracticeset-upisshowninfig.6(c)[29].Lengthofboreholesusedfordestressblastingdependsonsizeofprotectiveareawhichiscreatedaheadofafaceandthisisafunctionofthicknessofcoalseam,sizeofpillars,miningdepthandlocked-instressesinimmediateroofrocks(principlesarepresentedinFigure3).InPolishcollieries,lengthofboreholesisusuallyupto10m,diameterofboreholesdonotexceed80mm(usually42mm).Generallywecanquotethatsmallcharges(max.2.5kgsafetyexplosiveperborehole)areusedforboreholesindicatingexcessivestressstate.However,consumptionofblastingmaterialon1moflongwalladvanceisreportedabout80kg[28].Combinedsystemisfrequentlyusedindriving–destressblastingandcutblastingtogetherwherelengthofboreholesandexplosivechargearesmaller[28],lengthofboreholesfrom1.2to2.4mandexplosivechargeisfrom300gto1200gperborehole.Maximumwaitingtimeafterdestressblastingincoalseamis30minutes.InCzechCollieriesthelengthofboreholeislarger(upto20m),diameterofboreholes(42mm)andspacingofboreholes(max.5mindrivingofroadways,max.15minlogwallface)arestrictlygiven.Explosivechargeislarger(from2.5to7.5kgperborehole,i.e.50%–60%lengthofborehole).Maximumweightofexplosivechargeis180kgperdestressblastingstage.Combinationofdistressblastingincoalseamsanddestressdrillingaresometimesused[45];indrivingdestressboreholesinthefaceanddestressblastinginsidesofgates;inminingdestressboreholesfromgatewaysandtherestofthelongwallface–destressblasting.TypicalexampleofdestressblastinginCzechcollieriesispresentedinFigure6(c).InGermancollieries,destressdrilling(orslotting)ispreferredoverdestressblastinginmostcases.Rockburstphenomenaareobservedincoalseamsonly,anddestressdrillingisbelievedtobemoreeffective[46].ItisnoteworthythatthethicknessofcoalseamsinGermancollieriesgenerallydoesnotexceed3.5m.Generally,coaldepositsarefoundinmulti-seamseparatedfromeachotherby3m(termedascontiguousseams)tofewtensofmetersandtheyworkedinsequencefromtoptobottomexceptcontiguousseams.Oftenenough,partoftheupperseamisnotmineableandisletbehind.Miningoftheseambelowtheunminedportionoftheupperseammayposestrainburstinghazards.Suchasituationdemandstheapplicationofdestressblastingpriortotheminingofthelowerseam[e.g.2,35,47].Figure7.Simplifiedmodelofdestressblastingapplication[36]ApplicationofdestressblastingundersuchconditionshasbeeninpracticeinCzech[36,45,47,48]andPoland[22,23,28]andistermed"preconditioning"asdestressblastingispracticedmuchearlierthanmining.ThesimplifiedconceptualmodelofdestressblastingapplicationaspreconditioningisshowninFigure7[36].Thus,twomaintypesofrockburstsaredistinguishedaccordingtotheiroriginandmechanism.Theyare:rockburstinitiatedinthecoalseamoritsvicinityandrockburstinitiatedoutsidethecoalseam,mostlyinhighlycompetentroof.Toprotectagainstrockburstsinthecoalseam,activemeasuresareappliedinthevicinityofmineworkings,whereastoeliminateunfavourablestressconditionsoutsidethecoalseamitisnecessarytoapplypassiveprotectionofpotentiallyendangeredmineworkings.Wecangenerallydescribethepreconditioningsystemasasystemoflongholeswhicharedrilledinadjacentrocksofcoalseams.Preconditioningisdesignedaccordingtothefollowingspecifications[36].•Boreholesdrilledusuallyfromthegates.•Boreholesdiameter75–105mm.•Inclinationofboreholesupto+30°.•Spacingofboreholes5–12m.•Pneumaticchargingofexplosivesintoboreholes(incartridges).•Useofrockexplosives.•Simultaneousblastingwithoutdelay.•Blastingofexplosivesatadistanceof30mto100mfromthelongwallfaceintheregionofexpectedstressconcentration.Maximumwaitingtimeafterdestressblastinginadjacentrocksdependsonthedilutionofblast-inducedfumesinthemineandregisteredseismicactivity.Waitingtimeisfrom45to60minutes.Destressblastinginadjacentrocksofhardcoalseamsisnotthemostcommonlyusedsystemofcoalrockburstprevention.DestressblastingasarockburstcontroltechniquecomesfromdeepSouthAfricanoremines.Wecangenerallydescribemaingoalsofdestressblastingas:•Softeningofthecompetentrocklayersandreducingtheireffectivemodulusofelasticity,•Stressrelease.UsingsystemintheCzechCollieries,whichexampleispresentedbelow,isauniqueEuropeansystemindifficultstressconditionsinrockmasswecandescribeitwidely.Thesystemofdestressblastinghasbeenusedfor30yearsandwithincreasingminingdepths,ithasgainedimportance[36].AnexampleofdestressblastingaspreconditioningispresentedinFig.8whichhasbeenappliedinCSAcollieryoftheCzechRepublic[17].Theproperdestressblastingdrillholesweredrilledupwardsfrom(+20o)to(+28o)fromcoalseamlevelNo530locatedwithindepthrangeof860mupto890mbelowEarthsurface.Thelengthsofholesvariedfrom30mto80m.Inviewofdesignedparametersandthedestressblastingtasktheboreholediametersof75mmand93mmwereselected.Perpendiculardistancebetweenthedrillholesof(1)and(2)was10mupto15mandbetweenthedrillholesof(3)was10matmaximum.Thedrillholebottomsweresituatedatadistanceofabout30mabovetoppartofcoalseamNo530.Fordrillholestheplasticexplosiveinchargesaswellaspneumaticsandstemmingwereapplied.Thelengthsofparticularchargesvariedfrom15mupto50mandthelengthsofsandstemmingfrom15mupto30m.Allchargesineachstageweresimultaneouslyfiredwithoutusingdelays.Weightofparticularchargesvariedaccordingtoapplieddiameterandlengthofdrillholefrom60kgupto400kgperhole.Inparticularstagesthegroupsof2–6drillholeswithtotalchargesof552kgupto1440kgwereblasted.27stagesofdestressblastingwererealizedduringtheextractionoflongwallNo14735,i.e.fromNovember2003untilJune2004.Atotalamountof27,960kgexplosiveswasblastedin120drillholes.Inallstagesagreaterseismicenergywasreleasedthanitwouldcorrespondtoworkingperformedbyexplosiveatspecificphysical-mechanicalconditions.SimilarsystemofdestressblastingisusedinPolishcollieries[23,28,37],lengthofboreholesisintherangeof12to60mbutweightofexplosivechargeissmaller(accordingtolengthofboreholes40–150kg).Spacingofboreholesislarger(20–40m).Sometimesthegoalistocreatefracturesaroundtheblastedholes.DirectionalfracturingtechniquehasbeendevelopedinPoland[49,50].Thistechniqueisbasedontheconceptofhydraulicfracturingbuthasadjustmentfordestressblasting.Theobjectiveistocreatefracturesperpendiculartoboreholeaxis.MaximumwaitingtimeafterdestressblastingismuchlongerthaninCzechcollieries(uptoseveralhours).Fig.8.SchemeandsituationofdestressblastinginareaoflongwallNo14735inseamNo530atCSAColliery[17]4.EvaluationofeffectivenessProperlydesignedandrealizeddestressrockblasting(locationandspacingofboreholes,diameterofboreholes,lengthofcharge,numberoffiredboreholes,totalexplosivescharge,etc.)shallreducethestrengthanddeformationpropertiesofrockmassandthusshifthighstressconcentrationfartherinteriorintotherockmass.Evaluationofeffectivenessofdestressblastingisthusattemptedusingdifferentapproaches.Wewilltakeherealibertyofdescribingtheeffectivenessevaluationapproachasbeingdonefornon-coalminestooinordertodevelopabetterapproachforcoalmineapplications.Effectivenessfordestressblastingforthecaseofcutterfailureismeasuredfromvisualobservation.Incaseoffloorheave,theeffectivenessofdestressblastingismeasuredintermsofdecreaseinrockmassdeformationanddeformationrate.Kexinetal[25]andXiaetal.[26]describedecreaseinrockmassdeformationaftersuccessfulapplicationofdestressblastinginaChinesecoalmine.Figure9illustrateslongtermmeasurementofsidewallsandfloormovementcharacteristicsbeforeandafterdestressblastingintheChinesecoalmine.Variousattemptshavebeenmadetoascertaineffectivenessofdestressblastingasappliedtoalleviaterockburstproblemsandsomeofthemaredescribedbelow.Fig.9.Convergencemonitoringinacoalmineroadway[25]Changeinstressparametersbeforeandafterdestressblasting[35,38,39]andmodulusparameters[40,41]hasbeenmonitoredbothincoalandnon-coalminesasitisbelievedthattheobjectiveofdistressblastingistoreducethecriticalstressparametersandinducereductioninmodulusvaluessothattherockmassshallnotcarrycriticalstresslevel.Fig.10representsmeasurementofstresschangeduetodistressblastingintabulargolddepositsinSouthAfrica.Suchmeasurementsaretroubledwithinexplicableresults.Attemptshavealsobeenmadetocharacterizetheeffectivenessofdestressblastingbythecalculationofseismicenergyreleasedconcurrenttodestressblastingapplicationasitisconceivedthatreleaseofhigherenergythencontainedbytheexplosivesisamanifestationofreleaseofstrainenergystoredintherockmass[36,42].Theproblem,however,withtheapplicationofthismethodologyisthatmajorityofrockburstsareconcurrenttotheblasting,irrespectiveofroutineblastingordestressblasting.Stressreleaseisevaluatedusingcalculatedseismiceffect–SE[51,42].ItisbasedonstatisticalinterpretationofthedataofSEdistribution[42].Thedegreeofstressreleaseduetodestressblastingcanbedivided,onthebasisofSEcalculation,intoinsignificant,good,verygood,extremelygoodandexcellent(seeTable3).TheSEofdestressrockblastingistheratioofseismicenergyreleasedintherockmasswhenblastingtotheconsideredenergyoftheparticulardetonatedcharge:(1)whereESeis=seismicenergyinJ;Q=weightofexplosivechargeinkg;andK=2.1(forthenaturalconditionsofrockmassintheCzechpartoftheUSCB).ThereleasedseismicenergyintherockmassESeisisevaluatedfromseismicmonitoring.