powersiteground

UpgradingandApplicationofSmall-sizedDrillingRigintheProtectionofTransmissionTowernearDeepFoundationPitSHAOGuangBiao1,a*,WANGHuaJuan2,b1ShandongJianZhuUniversity,Jinan250100,China2ShandongElectricPowerEngineeringConsultingInstitutecorp.
,Ltd.
,Jinan250013,Chinaasgbou@126.
com,bwanghuajuan@sdepci.
comKeywords:transmissiontower;foundationpit;foundationunderpinning;micro-pile;drillingrig.
Abstract.
Thesmall-sizeddrillingrigsuchasXY-100iswidelyusedinsurveyengineering.
Withthedevelopmentofunderpinningtechnique,moreandmoremicro-pileshouldbedrillnearbuildingsandstructures.
Thehigherrigshelfshouldbeupgradedforsuitwithlimitedspace.
Theexcavationofdeepfoundationpitleadtosecurityriskswhenhighvoltagetransmissiontowernearthepit.
Basedonthefoundationunderpinningtechnologyandthedeepfoundationpitsupportingmethod,areinforcementdesignmethodisproposedfortransmissiontowerfoundationneardeepexcavation.
Inthemethod,theshallowfoundationoftoweristransformedintopilefoundationfirstlyusingmicro-pilewhichtransfertheloadstothedeepsoillayer.
Thenusingmicropilecompositesoilnailingwallsupportingtechnologytosupportfortheverticalexcavationofdeepfoundationpit.
Themicro-pilesaredrilledusingtheupgradingdrillrigandtheprotectionengineeringachievedsuccess.
IntroductionWiththespeedingupofurbanizationinourcountry,allkindsofcivilconstructionandpublictransportationinfrastructureincreasesrapidly,thedevelopmentandutilizationofundergroundspaceisincreasinginthecity,andsomeoftheengineeringconstructionapproachesforhighvoltagetransmissiontower,foundationpitexcavationinundergroundengineeringconstructioniseasytocausedeformationofsoil,leadingtodifferentialsettlementofthetransmissiontower,totheoverallstabilityofthetransmissiontowerandlargetransmissionsecurityhiddendanger,evencatastrophicconsequences.
Transmissiontowerof110kvlineislocatedinJinan,nearthenewmunicipalengineeringexcavationlineparalleltothebasiclinehorizontaldistanceisabout1.
5m,excavationdepthisabout8.
0mundernaturalgroundandnoslopespace.
Duetourgencyandnarrowlylimitedtimeschedule,thecornertransmissiontowershouldbeprotectedwhenfoundationpitexcavation.
Transmissiontowerfoundationgenerallydesignedwithfourindependentshallowfoundation,twobasictensile,compressionoftwobase.
Polesfoundationunevensettlementordeformationcausedlargetowertiltedwillbeinducedneartheexcavationoffoundationpit,whichwillthreatenthenormaluseoftransmissionlines.
Insomepracticalprojectsfortransmissionlinestomoveandthatrequiredalongerperiodandahigherprojectcost.
Thispapertakeadvantageofmicropile(alsocalledtherootpile,mini-pile)technologyofunderpinningreinforcement[1],guaranteethestabilityoftransmissiontowerfoundationandtakeitsloadtransfertothelowersoillayer.
Accordingtothecharacteristicsoftransmissiontower,thelargeconstructionequipmentarelimitedinthisprotectionengineering,thesmall-typedrillrigisupgradedandflexiblyworkedformicro-pilenearthepowertower.
Withthehelpofupgradeddrillrig,thejointuseofrootpileforfoundationunderpinningtechnology,andcompositesoilnailingsupportforfoundationpitexcavationintheprotectionofthetransmissiontowerprovidesareliabledesignmethod.
TransmissiontowerfoundationunderpinningtechniqueFoundationunderpinningisthefoundationoforiginalstructurereinforcementandchange,toimprovethebasicworkstate,suchasunevensettlement,thestructureofthebuildingwhentheloadincreases,etc.
Transmissiontowergenerallyadoptsthecast-in-placereinforcedconcreteshallowfoundation.
Topformadditionalloadareappearedneartheexcavationandbadforfoundationpitslopestability.
Acertaincornertowerfoundationarrangementasshowninfigure1.
withthehelpoffoundationunderpinningtechnology,theadditionalloadscantransfertodeepersoillayerandatthesametimeisconducivetothesettlementanddeformationcontrolofthetransmissiontowerfoundation.
Fig.
1TheplanofcornertowerfoundationCertainparticularityanddifficultyhadexistedintransmissiontowerfoundationunderpinning:(1)undertheoperationofthetransmissiontoweroperationandhighsafetyrequirements,large-scaleconstructionequipmentoperationishighlyrestricted;(2)reducingasfaraspossibleontheoriginalfoundationandthevibrationofthefoundation,toavoidaffecttherunningofthetransmissiontower.
Thereforefoundationunderpinningoftowershouldbegivensufficientconsiderationofconstructiontechnologyandmachineofpiletypeselectedtomeettheaboveconditions.
Micropiletechnologyonthebasisofthetransmissiontowerintheresearchfocusandgetmoreengineeringapplicationinrecentyears[2,3].
Micropileisakindofsmalldiameterpile,usingpressuregroutingprocessmachineryintoahole,thediameterislessthan350mm,generallypilelengthnotexceed30m.
Thepilecanbeusedinavarietyofarrangementofthestraightpileandinclinedpile,constructionfast,operationspaceissmallcomparedwiththeordinarypileetc.
Andmainlyusedinancientbuildingsprotection,foundationunderpinningandbracingengineeringofdeepfoundationpit.
Sowhentransmissiontowerfoundationunderpinningbymicro-pileprogramcanbettersolvetheaboveproblems:(1)micropileconstructionmachineryissimple,canusesmalldrilltopore-creatingwithintheplanesize1.
5m*2.
5mand2.
5mheadroom.
Thesmallrigshoulddrillaholethroughtheconcretefoundationandothersoillayer,andstrongadaptabilitytothesurroundingenvironment;(2)thepileholediameterissmall,poreformingprocessontheoriginalfoundationandfoundationsoilalmostdonotproduceadditionalstress,noiseandvibrationcausedbytheconstructionisverysmall,anddoesnotaffectthenormaluseoftransmissiontower;(3)Upperloadforcecanbedownwardclearly.
Meanwhilethesoilmechanicalcharacteristicscanbeimprovedthroughthesecondaryhighpressuregrouting,whichcaneffectivelyimprovethebearingcapacityofsinglepileandtheabilitytoresistoverturning.
Fig.
2isschematicdiagramoftransmissiontowerfoundationunderpinningbymicropile,micropilecanbeuseddirectlyorinclinedpiles,piletopandplantingbarfoundationthroughthenewcapandachieveeffectiveconnection.
Whenunderpinningusingrootpile,pilecanbethoughtofnoteffectduringconstruction.
Butaftertheunderpinningconstruction,baseevenproduceminimalsubsidence,micropilewillforcequicklyandtakepartofthestructureload,atthesametimereducebasalforceonsoillayer.
Ifstructurecontinuestosink,micropileofloadwillincreasegradually,untilalltheloadbornebythemicropile.
Becauseofthetinypilediameterissmall,bearingcapacityoffrictionpilecanbecalculatedonlywhenallpileinthesoil.
ThecompressivebearingcapacityofsinglepilecanbecalculatedbyEq.
1.
∑==nisikiupqLUP1(1)Intheformula:Uisthecircumferenceofpilebody;Liisthedepthoftheithlayerofsoil;qsikisthelimitofsoillateralresistancestandard,whenthesecondhighpressuregrouting,thevalueofqsikincreasedreferencetoJGJ94-2008tables5.
3.
10.
Fig.
2Foundationunderpinningwithmicro-pileMiniaturepilecompositesoilnailingwallsupportingtechnologyFoundationpitsupportingtypeismore,suchaspile-anchorbracingstructure,innersupportingstructureandsoilnailingwallstructure.
Thesoilnailwallsupportingareconsistedbytheinsitusoil,soilnailingandconcretesurface.
Throughsoilnail,thesurfacelayerandthecommonroleofundisturbedsoil,formedonthebasisoftheactiverestrictionmechanismofcomplex,hasgreatlyimprovedthestructureoftheslopesoilstrengthandresistancetodeformationability,decreasethelateraldeformationofsoil,enhancethestabilityoftheoverallcharacteristics.
Whennoslopespaceorlimitedtoconstructedtheschemeofcompositesoilnailingwallisused.
Thecompositesoilnailingwallisakindofcompositesupportingsysteminwhichthesoilnailingwallunitedandoneormoreofthefollowingindividualsupportingtechnology,suchaspre-stressedanchor,waterproofcurtain,micropile,etc.
Typicalminiaturepilecompositesoilnailingsupportsectionasshowninfig.
3.
Fig.
3MicropilecompositesoilnailingprofilesketchMiniaturepilecompositesoilnailingwallhasflexible,wideapplicablerange,lowcost,shortconstructionperiodandthecharacteristicsofsafeandreliable.
Inpracticalengineering,thecompositesoilnailingwallinallkindsoftechnologyaccordingtotheorganiccombinationofengineeringneedtobeflexible,sothattheconstructionissimple,economicandreasonable,comprehensiveperformanceisoutstanding,anddeformationandtheoverallstabilityoftheslopecanmeettherequirements.
DesignexampleEngineeringgeologicalprofile.
Accordingtothesurveyreport,theproposedsitebelongstothealluvialplainofsandsiltedgeomorphicunit,therootcauseoftheformationismainlyforquaternaryalluvialloam.
Thesoillayeraffectedfoundationpitengineeringmainlyinclude:(1)layerofgrainfilling,yellow-brown,maincompositionofash,gravelandclay,theaveragethicknessof2.
13m;(2)layersofclay,yellow-brown,plastic,toughnessanddrystrengthofmedium,accidentallyseesandandshells,theaveragethicknessof4.
19m;(3)layerandtheclay,taupe,plastic~hardplastic,toughnessanddrystrengthofmedium,theironmanganeseimpregnation,occasionalloess-dollandshell,theaveragethicknessof3.
38m;(4)layerandtheclay,brownyellow,plasticity,toughnessanddrystrengthofmedium,theironmanganeseimpregnationandtuberculosis,about5~25%loess-doll,particlesizeof2~5cm,theaveragethicknessof5.
24m.
Sitegroundwatertypequaternaryporewater,thewaterlevelduringtheexplorationdepthof10.
50~13.
81m.
Towerfoundationreinforcementdesign.
AccordingtoEq.
1andsoilparametersaccordingtothesurveyreport,pilediameterisdesignedfor220mm,built-in140mmdiameter,wallthickness5mmsteeltube,whentheeffectivepilelengthis15m,thebearingcapacitycharacteristicvalueofupto264kN,designvalueofsinglepilebearingcapacitycharacteristicis250kNandsatisfythepilebodymaterialcompressivestrengthofnormalsection.
Andbasisweightoftheupperstructureloadcalculation,eachindependentfoundationbaseloadabout1400kN,so6steelpipepilesshouldbearranged.
PilearrangementandlocalsectionasshowninFig.
4,duetoaquarteroftheindependentfoundationislocatedinsidethetowerframe,fortheconstructioninconvenienceandconsideringasymmetriceffect,setupfivestraightpile,twoinclinedpile,totalof7piles,towerbasedloadeffectivelytoensurethatthelowersoil.
Fig.
4TransmissiontowerfoundationunderpinningarrangementMiniaturepilecompositesoilnailingdesign.
AfterdeterminingtheAngletowerfoundationreinforcementscheme,soillateraldeformationduetofoundationpitexcavationandsupportdesignofthefoundationpitshouldbeconsidered.
Inviewoftheconstructionsiterestrictions,verticalslopeexcavationoffoundationpitbeadopted,usingmicropilecompositesoilnailingwallsupportingscheme,micropilediameter180mm,sameastheunderpinningpilebodymaterial,butnoneedforsecondarygrouting.
Miniaturepilebuilt-indepthof2.
0m,0.
75mhorizontalspacing;Supportingprofilesettinganchor2rowsand2rowssoilnailing,theirhorizontalspacingof1.
5m,andthehorizontalangleof15o.
Anchorneedtosetupthewaistbeamtensiontocontrolthedeformationofthefoundationpitwall.
SupportingdesignsectionasshowninFig.
5.
Fig.
5underpinningtechnologycombinedcompositesoilnailingsupportsectionThestabilityofcompositesoilnailingwallintegralcalculationisnotconsidertowerloadsanditsoverallstabilitycoefficientaremorethan1.
3,satisfiedwiththerelevantspecificationrequirements.
Inthesubsequentengineeringconstruction,theupgradeddrillrigsareusedforboringforunderpinningpileandsupportingpile,whichprovidesguaranteetofinishontimeforthemunicipalengineering.
SummaryBasedonminiaturepilefoundationunderpinningandcompositesoilnailingwallsupportingtechnology,thetransmissiontowerfoundationneardeepfoundationpitprotectedsuccessfullyusingupgradingsmall-sizeddrillingrig.
Indesignscheme:(1)thefoundationunderpinningdesignmakefulluseofcharacteristicsofmicropile,suchasconstructionspacerequirementsislow,theimpactonboththestructurecharacteristicsofbearingcapacityandclear,ensurethesmoothimplementationofthefoundationunderpinning,havecreatedfavorableconditionsforthefoundationpitexcavation;(2)thefoundationpitsupportingdesign,fullyconsiderminiaturepilesupportingroleinadvance,theuseofcompositesoilnailingwalltechnology,guaranteethestabilityofthefoundationpitslope.
Useofupgradingsmall-sizeddrillingrigtocreatemicropilesfordeepfoundationpitoftransmissiontowerfoundationunderpinningandthereinforcementdesignschemeofcompoundsoilnailing,verifiedbypracticalengineering,toprovidesimilartotheprotectionofthetransmissiontowerdesigneffectivetechnicalreference.
AcknowledgementsThisworkwasfinanciallysupportedbyNationalNaturalScienceFoundationofChina(51008183).
References[1]Y.
G.
Huang,F.
Zhou,Theapplicationofthemicrosteelpipepilesinfoundationreinforcementengineering,SichuanArchitecture,26(2006)76-77.
[2]R.
Z.
Su,W.
F.
Zheng,X.
L.
Lu,Y.
F.
Cheng,Experimentalonupliftingcharactersofmicropilesoftowerfoundationsinsoftsoils,Electricpowerconstruction,12(2008)23-25.
[3]D.
P.
Liu,Transmissionlineanalysisoftheapplicationofmicro-pilefoundation,Anhuielectricpower,2(2009)35-38.