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RockBlastingTechnique - I

By:Dr.Ir.SinggihSaptono,MT.Dr.Ir.S.Koesnaryo,M.Sc.

Dr.Ir.BarlianDwinagara,MT.Ir.R.Hariyanto,MT.

HANDOUT

MiningEngineeringDepartment– FacultyofTechnologyMineralUniversitasPembangunanNasionalVeteranYogyakarta

February,2016

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RockDrillingMethodLesson5

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tRockDrilling

• Rockdrilling,inthefieldofblasting,isthefirstoperation carriedoutanditspurposeistoOpenholes,withthe adequategeometryanddistributionwithintherockmasses,wheretheexplosivechargeswillbeplacedalongwiththeirinitiatingdevices.

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tThesystemsofrockdrillingthathavebeendeveloped andclassifiedaccordingtotheirorderofpresentday applicabilityare:

• -Mechanical:Percussion,rotary,rotary-percussion.• - Themzal:Flame,plasma,hotfluid,Freezing.• - Hydraulic:Jet,erosion,cavitation.• - Sonic:Highfrequencyvibration.• - Chemical:microblast,dissolution.• - Electrical:Electricarc,magneticinduction.• - Seismic:Laserray.• - Nuclear:Fusion,fission.

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TypesofDrillingOperationsUsed in RockBreakage

• Manualdrilling.Thisiscarried outwithlightequipment thatishandheldbythedrillers.Itisusedinsmall operationswhere,duetothesize,othermachinerycannotbeusedoritscostisnotjustified.

• Mechanizeddrilling.Thedrillingequipmentis mounteduponrigswithwhichtheOperatorcancontrolall drillingParametersfromacomfortableposition.These structuresorchasis canthemselvesbemountedonwheelsortracksandeitherbeself-propelledortowable.

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tThetypesofwork,insurfaceaswell asinundergroundoperations,canbeclassifiedinthe followingsgroups:

• Benchdrilling.Thisisthebestmethodforrock blastingasafreefaceisavailablefortheprojectionof materialanditallowsworkto besystemized. Itisusedinsurfaceprojectsaswellasinundergroundoperations,usuallywithverticalblastholes,although horizontalholescanbedrilledonoccasion.

• Drillingfordrifting andtunnelling.Aninitialcavity orcutmustbeopenedtowardswhichtherestofthe fragmentedrockfromtheotherchargesisdirected.Blastholedrillingcanbecarriedoutwithhandhelddrills,but thetrendistowardstotalmechanization,usingjumboswithoneorvariousbooms.

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t• Productiondrilling.Thistermisusedinmining operations,fundamentallyunderground,todescribethe laborsoforeextraction.Theequipmentandmethods usedvarywiththeexploitationsystems,havingthecommon factoroflittleavailablespaceinthedriftsforblastholedrilling.

• Drillingforraises.Inmanyundergroundandcivil engineeringprojectsitisnecessarytoOpenraises.Although thereisatendencytoapplytheRaiseBoringmethod,stilltodaythelongblastholemethodisusedas wellasotherspecialdrillingsystemscombinedwith blasting.

• Drillingrockswithoverburden.Thedrillingofrockmasseswhicharecoveredwithbedsofunconsolidatedmaterialscallsforspecialdrillingmethodswithcasing. Thismethodisalsousedinunderwateroperations.

• Rocksupports.Inmanyundergroundoperationsand sometimesinsurfaceonesitisnecessarytosupportthe rocksbymeansofboltingorcementingcables,inwhich drillingisthefirstphase.

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Fieldsof ApplicationforThe DifferentDrillingMethods

• Rotary-percussivemethods.Thesearethemostfrequentlyusedinalltypesofrocks,thetophammer aswell asthedown-the-holehammer.

• Rotarymethods.Thesearesubdividedintotwo groups,dependinguponifthepenetrationiscarried out bycrushing,withtricones orbycutwithdragbits.The firstsystemisusedinmediumtohardrocks,andthe secondinsoftrocks.

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RockPropertiesThatAffectDrilling

Theprincipalphysicalrockpropertiesthathaveinfluenceuponpenetrationmechanismsand,asaconsequence,on choiceofthedrillingmethodare:

1. Hardness,2. Strength,3. Elasticity,4. Plasticity,5. Abrasiveness,6. Texture,7. Structure,8. Characteristics ofbreakage.

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t1.Hardness• Hardnessisconsideredtobetheresistanceofasurface layertobepenetratedbyanotherbodyofharderconsistency.

• Inrock,itisafunctionofthehardnessandcompositionofitsmineralgrains,theporosity,degreeofhumidity, etc.

• Thehardnessofrocksistheprincipaltypeofresistance thatmustbeovercomeduringdrilling,becauseoncethe bithaspenetrated,therestoftheoperationiseasier.

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t2.Strength

Mechanicalstrengthofarockisthepropertyofopposingdestructionbyanexternalforce,eitherstaticordynamic.Therocksgivemaximumresistancetocompression,normally,asthetensilestrengthisnotmorethan10or 15%ofthecompressivestrength.Thisisduetothefragilityofrocks,tothelargequantityoflocaldefectsandirregularitiesthatexistandtothesmallcohesionbetween theparticlesofwhichtheyareconstituted.

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t3.Elasticity

• Themajorityofrockmineralshaveanelastic-fragile behavior,whichobeystheLawofHooke,andaredestroyedwhenthestrainsexceedthelimitofelasticity.

• Dependinguponthenatureofdeformation,asfunction oftheStressesproducedbystaticcharges,threegroupsof rocksaretakenintoconsideration:1)Theelastic-fragile orthosewhichobeytheLawofHooke,2)Theplastic-fragile, thathaveplasticdeformationbeforedestruction,3)Thehighly-plasticorveryporous,inwhichtheelastic deformationisinsignificant.

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t4.Plasticity

• Theplasticitydependsuponthemineralcomposition oftherocksanddiminisheswithanincreaseinquartz content,feldsparandotherhardminerals.Thehumid claysandsomehomogeneousrockshaveplasticproperties.

• Theplasticityofthestonyrocks(granites,schistoses,crystallines andsandstones)becomesnoticeable especiallyathightemperatures.

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5.Abrasiveness• Abrasivenessisthecapacityoftherockstowearawaythe contactsurfaceofanotherbodythatisharder,inthe rubbingorabrasiveprocessduringmovement.

• Thefactorsthatenhanceabrasivecapacitiesofrocks arethefollowing:a. Thehardnessofthegrainsoftherock.Therocks thatcontainquartzgrains

arehighlyabrasive.b. Theshapeofthegrains.Thosethatareangulararemoreabrasivethanthe

roundones.c. Thesizeofthegrains.d. Theporosityoftherock.Itgivesroughcontact surfaceswithlocalstress

concentrations.e. Theheterogeneity.Polymineral rocks,although theseareequallyhard,are

moreabrasivebecausethey leaveroughsurfaceswithhardgrainsas,forexarnple, quartzgrainsinagranite.

• Thispropertyhasgreatinfluenceuponthelifeofdrill steelandbits.

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t Themeanamounts ofquartzfordifferent typesofrockareindicated

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t6.Texture

• Thetextureofarockreferstothestructureofthegrainsof mineralsthatconstituteit.Thesizeofthegrainsarean indication,aswellastheirshape,porosityetc.Allthese aspectshavesignificativeinfluenceondrillingperformance.

• Whenthegrainshavealenticularshape,asinaschist, drillingismoredifficultthanwhentheyareround,asina sandstone.

• Thetypeofmaterialthatmakesuptherockmatrixand unitesthemineralgrainsalsohasanimportantinfluence.

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7.Structure

•Thestmctural propertiesoftherockmasses,suchas schistosity,beddingplanes,joints,diabases andfaults,as wellastheirdipandstrikeaffecttheallignment ofthe blastholes,thedrillingperformanceandthestabilityof theblasthole walls

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t Propertiesofrocktypesaccordingtoorigin-basedclassification.

1 MPa = 1 MN/m2= 10 kg/cm2 = 142.2 psi

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tClassificationoftherockmasses

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t RotaryPercussiveDrillingTophammer.Inthesedrills,twoofthebasicactions,rotationandpercussion,areproducedoutsidetheblasthole,andaretransmittedbytheshankadaptorandthe drill steeltothednll bit.Thehamrnerscanbedriven hydraulicallyorpneumatically.

Downtheholehammer.Thepercussionisdelivered directlytothedrillbit,whereastherotationisperformedoutsidethehole.Thepistonisdrivenpneumatically,whiletherotationcanbehydraulicorpneumatic.

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RockBlastingTechniqu

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tThemainadvantagesofrotarypercussivedrilling are:

• Itcanbeappliedtoanytypeofrock,fromsofttohard.

•Widerangeofdiameters;•Versatileequipment, itadaptswelltodifferentoperations andisveryMobile;

•OnlyrequiresoneOperator;•Easy,quickmaintenance,and•Thecapitalcostisnothigh

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tRotarypercussiondrillingisbaseduponthe

combination ofthefollowing:

• Percussion.Theimpactsproducedbyrepeated blowsofthepistongenerateshockwavesthataretransmitted tothebitthroughthedrillsteel(intopharnmer)or directlyuponit(downthehole).

• Rotation.Withthismovement, thebitisturnedso thattheimpactsareproducedontherockindifferent positions.

• Feed,orthrustload.Inordertomaintainthecontact ofthednll bitwiththerock,athrustloadorfeedforceis appliedtothedrillsiring.

• Flushing.Flushing removesthedrillcuttingsfrom theblasthole.

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t• Percussionoutputpowerinpercussivedrillingisproducedbytherock drill’simpactenergyandfrequency.

• Pneumaticdrillinghasatypical impactfrequencyofbetween1,600- 3,400hitsperminute;hydraulicdrilling,2,000- 4,500hitsper minute.

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PercussionDrillRigs

Percussiondrillcanbeair– orhydraulic– operatedandaregenerallylimitedtoholediameterof5inchesorless.

Percussiondrillusebuttonorcross(X-typedrillbitsinwhichthecuttingtoolismadeofhardtungstencarbide.Wingangleandbuttonconfigurationsaredesignedtoaccommodatesofttohardformationsandcomeinavarietyofconfigurations.

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t• DTHhammers,withthepistoninthehole,tendtodrillstraighterholesatgreaterdepthascomparedtoOTHdrifters.Theair-drivenpistonhammercausesthebittorapidlyimpacttherockwhilethebitisslowlyturned.DTHhammersareefficientinhard-rocktypes.Withthehammerinthehole,drill-pipevibrationsareeliminated

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t Steeltoothbitselection

• Softformationbits,TheTypeS,regularcirculationsteeltoothbitisdesigned foroptimumperformanceinformationsoflowcompressivestrength,suchassoftsandrock,calcite,shaleand clay.Theseformationsquiteoftencontainabrasivematerials suchassharpsandandmaybeinterspersedwith layersofmediumandhardformations.

• Mediumformationbits,TheTypeMandregularcirculationsteeltoothrackbits aredesignedforabrasiveandnon-abrasivemediumformations. Notethatthisdesigndiffersfromthe“softer” typesprincipallyintheprogressivestrengtheningof theteethandchangeinbitgeometrytoprovidemore chipping-crushingaction.Thesebitshavemoreclosely spacedteethwithalargeincludedangleandmoregage surfacetoresistthewearinharderandmoreabrasiveformations.

• Hardformationbits,TypeH,regularcirculationsteeltoothrockbitsaredesigned todrillhardformationswhichcontainamounts ofabrasivematerials.

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H Series

M Series

S Series

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t Whentochangeabit

• AttheendofaTriconebitslifethecuttingstructurebecomesineffectiveeitherthroughbreakageorwear, resultinginreducedpenetrationrate.

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RockDrillingEquipment

• IntegralDrillSteel

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Blasthole Patterns

Bench Blast Pattern in Quarry / Open Pit

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tBlastholes /Initiationpatternsforshotsfiredtoanopenface

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t UNDERGROUNDBLASTING

Pyramidordiamondcut(afterICI)Wedgecut(afterICI)

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Burncut(afterICI)

Fancut

Dragcut