Main Characteristics and Technical Countermeasures for Blast Cutting of Frozen Earth in the Area.docx
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MainCharacteristicsandTechnicalCountermeasuresforBlastCuttingofFrozenEarthintheArea
MainCharacteristicsandTechnicalCountermeasuresforBlastCuttingofFrozenEarthinthePlateauArea
Abstract:
Basedontheblastexperimentresultsachievedin1974-1977onthefrozenearthinFenghuoMountainandQingshuiriverinKekexiliareaofQingghai-Tibetplateau,thispaperdescribestheimportanceofentironmentprotectionduringtheblastingoffrozenearthintheplateau.Accordingtothegeologicalandclimatecharacteristic,itputsforwardthetechnicalcountermeasuresfortheblastdrill,protectionofblastequipmentfromwater,freezeandthunder,introducestheblastdesignandthecuttingofrailwaycutandthefoundationpitofthebridgeandculvertonfrozenearth.Italsopointsoutthatwhentheprincipleofholdingthefrozenisfollowed,theblastingshouldbedoneincoldseason,whilefortheprincipleofthawing,warmseasonismoreapplicable,buttheblastshouldmeetthetechnicalrequirementoffastconstructionfortheblastcuttingengineering.
Keywords:
Xining-LhasarailwayFrozenearthofplateauareaBlastequipmentBlasttechnology
1.Forewords
ChinesegovernmenthaslaunchedtheconstructionofXining-Lhasarailway.StartingfromGolumd,QinghaiprovinceintheeastandendinginLhasa,Tibetinthewest,thelinehasatotallengthof1118km.550kmofthelinehavetobebuiltonthefrozenearthoftheplateau.TheblasttechnologyforfrozenearthoftheplateauisthekeytechnicalissuefacedbytheconstructionteamofXining-Lhasaline.Asearlyasin1974-1977,theMinistryofRailwayshadsetupexperimentengineeringprojectinFenghuoMountain(withaltitudeof4500m)andQingshuiriver(4700m)inKekexiliareaofQingghai-Tibetplateauforscientificexperimentaimedatrailwayconstructiononthefrozenearthoftheplateau.Theexperimentscovertheblast-holedrillforbuildingtherailwaycutandthefastblastcuttingforthefoundationpitofthebridgeandculvert.Basedontheachievementsoftheaboveexperimentsandincombinationwiththedevelopmentoftheblastequipmentandthetechnologyinthelasttwodecades,thepaperdescribesthemaincharacteristicsandtechnicalcountermeasuresoftheblastcuttinginthefrozenearthareaoftheplateau.
2.Generaldescriptionsoftheexperimentoftheblastcuttinginfrozenearthareaoftheplateau
In1975andMay-September,1976,thefollowingexperimentshadbeencarriedoutonthefrozenearthinFenghuoMountainandQingshuiriverinKekexiliarea.
(1)Drillexperimentforthefrozenearth.Theexperimentistoexaminethedrillingspeedandperformanceofthefollowingdrillsforthefrozenearth:
type71-05smalldrill,theXJ-100handdrillforgeologicalpurpose,theDPP-100motorcardrill,theDG-1drillforpostinstallingcarandthetwistdrillmadebytheAcademy.
(2)Theexperimentonsuchcharacteristicsaswater-proof,freeze-resistance,burstandsafetyofthePoly-2slurryexplosiveandtherelatedblastingdevices(ammoniumnitrate,detonatorandexplosivetrain,etc.).Theresultshavebeenappliedinthefield.
(3)Theexperimentontheprimarydataofthefrozenearthblasting.Itincludesthestandardblastingconeandtheblastingexplosive-holechambering.Italsocoverthetestandmeasurementofthelayoutoftheexplosivecartridges,therelationshipbetweenthedrillholespace,rankspaceandholedepth,aswellasthedestroyandcompressionradiusoftheblasting.
(4)Theexperimentonblast-holedrillinganddeepexplosive-holechamberingforthe40mlongrailway-cutintheFenghuoMountaintestfield.Thedepthoftherailway-cutis5~7mandwidthoftheearthsurfacecuttingis15~20m.Thetrackshoulder(withslopeof1:
1.5)isprotectedwithretainingwallandallkindsofheatinsulationmaterialsrespectively.Thefoundationbaseofthecutistreatedbyfinegrainsoiltakingfromtheworksite.Theeffectivecapacityoftheexplosionis1820m3withloadingamountof1108kg.
(5)TheexperimentfortwofoundationpitsofthebridgeandculvertintheQingshuirivertestfield.(Thepitshaverespectivelythebuilt-upconcretepre-castingandthecoldconcretepouringfoundationbase,thecuttingcapacityis100m3and140m3inrespective).Thefoundationpitwasformedonthesamedaytheblastingwascompleted.ThecuttingwasfulfilledbytypeW46grab.
Inaddition,primaryexperimentforblastdrillingonthefrozenearthwascarriedoutinthesamefieldbyusingthreedifferenttypesoftenpoly-energybomb(50%and50%TNT)..
Fortheexperimentfield,thenaturalmountainslopeis5~10o,theoriginalearthsurfacegreenswardcoverageis80~90%andthethicknessofthegreensward0.15~0.20m.About1.55mdepthofearthisyearsfrozensavagenessupperlimit,1.55~2.0mearthissoilcontainedicelayer,withbulkicecontainingof80~90%.Theframeworkisofamaranthsandyclayanddebris.2.0~2.8mofearthisicesaturatedlayer,withbulkicecontainingof60~70%.5.3~7.0mearthislessormoreicefrozenlayer,withbulkicecontainingof5~10%.Theframeworkisofamaranthsandyshaleweatheredzone.Thetemperatureofthetestzoneis-1.5℃~-5℃foryears.
3.Maincharacteristicsoftheblastcuttinginfrozenareaoftheplateau
ThegeologicalproblemoftheyearsfrozenearthintheQinghai-Tibetplateauisthatforthehighicecontainingfrozenearthwithhigherannualaveragetemperature(suchastherichicefrozenearth,thesaturatedicefrozenearthandsoilcontainingice),thewaterinthesoilisunstable(eitherfrozenormelted)iftheearthlayerconsistsoffinegrainsoil.Theearthlayerisverysensitivetosuchelementsasclimatechange,engineeringconstruction,cutting,trafficandhumaninterference.Whenthethickundergroundicelayerisexposedtotheearthsurfaceordisturbed,theundergroundicewillmeltandresultinpitfall,heatmeltingandslidesinkaswellassolifluction.Inthiscase,theengineeringwillbeaffectedbysuchgeologicalphenomenalasfreezingexpansionandmeltingsink.
Theblastcuttingintheexperimentalfieldindicatedthattheremoveofthegreenswardsfromearthsurfacebeforetheconstructioninsomesectionshasresultedinmeltingcollapseinsomeareasandcausedserioussolifluction.Whichhasbroughtaboutgreatdifficultiesfortheconstruction.Duetooxygenshortageintheplateau,thedrillmachineishardtostartanditsefficiencyislow.Theblast-holedrillingmaysufferfromsiltreturningorre-freezingatanytime.Theexplosivedevicehasblastresistantproblemincasethewaterproofandanti-freezingmeasuresarenottakenproperlyortheloadingtimeintheholeistoolong.Afterblasting,theexposedburstheapandthefoundationpitmaymeltrapidly.Themeltinginthefoundationcouldbe16-18cmintwodays.Fortheburstheap,thethawingisevenmoreserious.Incasethecuttingandthespreadingofheatinsulationlayeraredelayed,itmaycausemeltingcollapseandslideandresultinengineeringdisease.
TheQinghai-Tibetplateauislackofoxygenandtheweatherisverychangeable.Theareaisalwayshitbystrongwind,snowstormandthunderandlightning.Duetothecomplexgeologicalconditionsandterribleconstructionenvironment,theblastcuttingtechnologyforthefrozenareaofplateauhastofacethefollowing:
(1)Ithastominimizeandcontrolthedisturbanceoftheblastcuttingtotheyearsfrozenearth,suchastocarryouttheblastcuttingstrictlyinaccordancewiththecuttingclearance.Protecttheentironmentfrombeingdestroyedbytheblastcuttingprocess.Removethewasteandcutearthsoonaftertheblastisfulfilledandspreadtheheatinsulationlayerandfillbackthesoilassoonaspossible.
(2)Therearecoldandwarmseasonsforfrozenearthareaofplateau.Themelting,groundtemperatureandphysicalmechanicsoffrozenearthvaryindifferentseason.Thiswillaffecttheblastdesignparametersoreventheselectionoftheblastcuttingsolutions.
(3)Theparticularityofthefrozengeologicalconditionsandtheenvironmentofoxygenshortagealsohavefreshrequirementontypeselectionofblastdrillingmachinesanditsoperationefficiency.
(4)Theblastequipmentusedforfrozenearthofplateaushouldbewater-proofandanti-freezing.Thestrongwind,snowstorm,thunderandlightning,aswellasthestrongultravioletradiatorwillbringaboutproblemsneverexperiencedforthestorage,transportoftheblastequipmentandblastcuttingaswell.Therefore,technicalcountermeasuresshouldbetakentoensurepropermanagement,safeoperationoftheequipment.
4.Blastholedrillingofthefrozenearth
4.1Drillingmachineusedforthefrozenearth
Duetothespecialgeologicalconditionsofthefrozenearth,pneumaticstriketypesinkholedrillingtrolleyordrillshouldnotbeadoptedinthewarmseason.Duringthetest,suchtwistdrillsasthe71-50smalldrill,XJ-100geologicaldrill,DDP-100motorcardrillandDG-1postinstallingcardrillhavebeenused.However,therarenessoftheair(atmospherepressureisabout560-600millibar)intheplateauareahascausedlowefficiencyofdrillingoperation.Forinstance,therealoperationrevolutionofthedrillisonly17-20rev./min.incomparewiththedesigneddataof80rev./min.Theaverageadvanceofeachdrillpershiftis4.0~10.1m.Evenwhentheself-madetwistdrillingbitisused,thepureaveragerateisonly0.11m/min.Undertheactionofthedrillmelting,thefrozencuttingmaterialhasbecomestickymudpiesthatarepressedbetweenthetwistvanesanddifficulttobethrownaway.Thisalsoresultedinlowefficiency.Therefore,inordertocopewiththerequirementthelarge-scaleconstruction,itisne