爆破在井巷掘进中的应用.docx

爆破在井巷掘进中的应用.docx

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爆破在井巷掘进中的应用

APPLICATIONOFBLASTINGINDRIVINGTUNNEL

1FRAGMENTATION

Fragmentationisthebreakingofcoal,ore,orrockbyblastingsothatthebulkofthematerialissmallenoughtoload,handleandtransport.Fragmentationwouldbeatitsbestwhenthedebrisisnotsmallerthannecessaryforhandlingandnotsolargeastorequirehandbreakingorsecondaryblasting.

Energymustbesuppliedtorockbydirectorindirectmeanstofragmentthatrockandthetypeofloadingsystem.Fragmentationenergyisconsumedbythemainmechanisms:

（1）creationofnewsurfacearea（fractureenergy）,

（2）friction（plasticity）and（3）elasticwaveenegydispersion.

Theloadingmethoddeterminestherelativeproportionsandtheamountofenergyconsumedinfragmentingagivenrocktype.Unonfinedtensilefailureconsumestheleastenergywithanincreasinga,mountofenergyrequiredastherockismorehighlyconfinedwithinacompressivestressfieldduringfragmentationThewayenergyisappliedbytoolstocauserockormineralfragmentationisimportantindeterminingfragmentationefficiency.Tobestdesignfragmentationtoolsandoptimizefragmentationsystemsitwouldbedesirabletoknowhowrockpropertiesinfluencebreakage.

Thestrengthofrockisinfluencedbytheenvironmentalconditionsimposedontherock.Thoseofmostimportanceinrockare

（1）confiningpressure,

（2）porefluidpressure,（3）temperatureand（4）rateofloadapplication.Increaseinconfiningpressure,aswithincreasingdepthbeneaththearth'ssurfaceorundertheactionofafragmentationtool,causesanincreaseinrockstrength.Apparentrockstrengthdecreasesasporcfluidpressureincreases,sinceitdecreasestheeffectofconfiningpressure.Althoughchemicaleffectsofporefluidsinfluencerockstrength,theygenerallyaresmallcomparedtotheconfiningpressureeffect,exceptforasmallminorityofrocktypes.Increaseinrocktemperaturecausesadecreaseinrockstrength.Thiseffectisverysmallbecauseofthesmallambienttemperaturechangesfoundduringmining.Anincreaseinrateofloadapplicationcausesanapparentincreaseinrockstrength.

Rockexhibitsdirectionalpropertiesthatinfluencethewayitbreaks.Theseareembodiedintheconceptofrockfabric,whichconnotesthestructureorconfigurationoftheaggregatecomponentsaswellasthephysicalormechanicalpropertymanifestations.Rockfabricontonlyrelatestothepreferredorientationofmineralconstituentsandtheirplanesofweakness,butalsototheconfigurationofdiscontinuities,microcracksandpores.Jointsandbeddingplaneshavegreatinfluenceonfragmentationatfieldscale.

Physicalpropertiesofrock（density,indentation,hardness,abrasivehardnessandporosity,）arefrequentlyusedinconjunctionwithmechanicalpropertiestodevelopbetterempiricalestimationsofrockfragmentation.

2BLASTHOLECHARGINGMETHODS

Drillholechargingcanbecarriedoutindifferentwaysdependingonwhethertheexplosiveusedisincartridgesorintheformofloosematerial.Theoldestchargingmethodimpliestheuseofatampingrodandthissystemisstillusedtoaverygreatextent.Duringthelast20years,compressedairchargershavebeenusedandthesemachinesprovidebothgoodcapacityandalsoanimprovedlevelofchargeconcentrationsothatthedrillholesareutilizedtoahigherdegree.Duringthelastfewyearssemi-automaticchargershavebeentakenintouse,primarilyinundergroundwork.Compressedairchargersforblastingpowderintheformofloosematerialhavealsocomeintouseonalargescale.Asfarasslurryblastingisconcerned,specialpumpingmethodshavebeendevelopedthroughwhichchargingcapacityinthecaseoflargediameterdrillholesispracticallygood.

Atampingrodmustbemadeofwoodorplastic.Itmustnotbetoothickinrelationtothedrillholediametersincethiscancrushanddamagefuseorelectricdetonatorcablesduringchargingwork.Ifagooddegreeofpackingistobeobtainedduringchargingwithatampingrodthenonlyonecartridgeatatimeshouldbechargedandtamped.Thedetonatormustbecorrectlyfedintothedrillholeduringchargingwork.

CompressedairchargershavebeeninuseisSwedenforabout20years.Thefirsttypeconsistedofaluminumpipesconnectedtogetherandthecartridgeswereblownintotheholewithanairpressureof42poundspersquareinch.sincethattimethechargingtubehasbeenreplacedbyanti-statictreatedplastichoseofaspecialdesign.Achargerincludesafoot-operatedvalve,reductionvavlewithairhose,breech,connectingtubeandcharginghose.

Thesemi-automaticchargerpermitsthecontinuousinsertionofexplosivecartridgeatthesamerateastheyarechargedintheholebythehose.Insteadofavalvebeingused,thecartridgespassthroughanairlockbetweentwoflaps.Theairpressureinthecharginghoseisretainedwhilecartridgesarepressureinthecharginghoseisretainedwhilecartridgesarebeinsinserted.Thesemi-automaticchargerpermitsconsiderablyhigherchargingcapacitythanthenormaltypeofcharger.

Explosivesintheformoftheformofloosematerial,usuallyammoniumnitrateexplosives（ANFO）,requirespecialchargers.Twotypescanbedifferentiated:

pressrurevesselmachinesandejectorunits.PressurevesselmachinesareparticularlysuitableforcrystallineAnexplosiveswithgoodchargingcapacity.Ejectorunitsareoperatebyanejectorsuckingupexplosivefromacontainerthroughacharginghose.Theexplosiveisthenblownthroughthecharginghoseintothedrillhole.Thereare,alsocombinedpressureejectormachines.ThecharginghoseusedforANFOchargingoperationsmustconductelectricityandhavearesistanceofatleast1KΏ/mandmax.30KΏ/M.

NitroNobelhasdevelopedaspecialpumpingprocedurewhichconsistsofatankervehiclewhichisusedtopumpexplosivedirectlythedrillholes.Thechargingcapacityisveryhighinthecaseoflargediameterdrillholes.

3CONTROLLEDBLASTINGTECHNIQUTES

Controlledblastingisusedtoreduceoverbreakandminimizefracturingoftherockattheboundaryofanexcavation.Thefourbasiccontrolledblastingtechniquesare:

linedrilling,presplitting,cushionblastingandsmoothblasting.

Linedrilling,theearliestcontrolledblastingtechnique,involvesdrillingarowofcloselyspacedholesalongthefinalexcavationline,providingaplaneofweaknesstowhichtobreak.Linedrillholes,2or4diametersapartandcontainnoexplosive.Theblastholesadjacenttothelinedrillholesnormallyareloadedlighterandareoncloserspacingthantheotherblastholes.Themaximumdepthforlinedrillingisabout30ft.Linedrillinginvolvesnoblastinginthefinalrowofholes,andthusminimizesdamagetothefinalwall.

Presplitting,sometimescalledpreshearing,involvesasinglerowofboreholes,usually2to4in.indiameter,drilledalongthefinalexcavationataspacingof6to12boreholediameters.Dynamitecartridges1to1.5in.insizeon1to2ft.centersusuallyarestring-loaddeondetonatingcord,althoughspecialsmall-diametercartridgeswithspecialcouplersareavailablefortotalcolumnloading.Inunconsolidatedformations,closerspacingswithlighterpowderloadsarerequired.Thebottom2to3ft.ofboreholeusuallyisloadedsomewhatheavierthantheremainder.Stemmingbetweenandaroundtheindividualchargesisoptional.Thetop2to3ft.ofboreholeisnotloaded,butisstemmed.Thedepththatcanbupresplitislimitedbyholealignment,with50ft.beingaboutmaximum.Thepresplitholesarefiredbeforebeforetheadjacentprimaryholestoprovideafractureplanetowhichtheprimaryblastcanbreak.Inpresplittingitisdifficulttodeterminetheresultsuntiltheadjacentprimaryblastisshot.Forthisreason,presplittingtoofarinadvanceisnotrecommended.Presplittingseldomisdoneunderground.

Cushionblastinginvolvesdrillingarowof2–to6-in.diameterboreholesalongthefinalexcavationline,loadingwithalightwell-distributedcharge,completelystemmedandfiringafterthemainexcavationisremovedratherthanbefore,asinpresplitting.Theburdenontheholesisslightlylargerthanthespacing.Wedgesmaybeusedtoabutthechargestotheexcavationsideoftheboreholeandminimizedamagetothefinalwall.Eeplosiveloadingissimilartothatinpresplitting.Cushionblastinghasbeendonetodepthsnear100ft.inasingleliftwiththelarger-diameterboreholesbecausealignmentismoreeasilyretained.Cushionblastingseldomisdoneunderground.

Smoothblastingistheundergroundcounterpartofcushionblasting.Attheperimeterofthetunnelordrift,closelyspacedholeswithaburden-to-spacingrationear1.5:

1areloadedwithlightwell-distributedcharges.Smoothblastingdiffersfromcushionblastinginthat

（1）exceptatthecollar,thechargesarenotstemmedand

（2）theperimeterholesarefiredonthelastdelayinthesameroundastheprimaryblast.Totalcolumnloadingismostcommon,althoughspacersmaybeused.Theholesarestemmedtopreventthechargesfrombeingpulledoutbythedetonationofthepreviousdelayedholes.Smoothblastingreducesoverbreakinadriftandalsoprovidesamorecompetentbackrequiringlesssupport.Itinvolvesmoreperimeterholesthandoesnormalblasting.

Combinationsofcontrolledblastingtechniquesareused.Inunconsolidatedrock,linedrillingsometimesisdesirablebetweenpresplitorcushionboreholes.Cornerssometimesarepresplitwhencushionblastingisused.

4TUNNELBLASTING

Themostcommonmethedofdrivingaminingtunnelisacyclicoperationinthreesequences:

（1）Drillingshotholes;chargingthemwithexplosivesandblasting.

（2）Removingtheresultingmuckpile.

（3）Insertingthetunnellining