1、The effect of resin annulus on anchorage performance of fully encapsulated rockbolts PCHaganTheUniversityofNewSouthWales(UNSW),SydneyA diverse selection of rockbolt designs and resin anchors are available for use inundergroundmines.ResearchinrecentyearsattheUNSWMiningResearchCentreledtotheconstructi
2、onofarockboltpulltestingfacility.Thisfacilityhassubsequentlybeenupgraded,commissionedandinitialtestworkhasbeencompletedtoverifythepulltestprocess.Atestprogramhasbeencompletedwiththeobjectivetounderstandtheloadtransfermechanismandimprovethegeneralperformanceofrockbolts.Thispaperdescribestheresultsoft
3、hisresearch.INTRODUCTION Rockbolts are increasingly relied on as a keycomponent in the primary support mechanism ofmany underground mines.In the Australian coalminingindustry,forexample,over5millionrockboltsareinstalledeachyearatacostofover$A35million.PreviousresearchbyUNSW,StrataControlTechnology P
4、ty Ltd(SCT)and Powercoal Ltd hasfoundthatover30%ofrockboltsarenotprovidingoptimumperformanceincoalminingenvironments(Galvinetal2001).Aresearchinitiativehasbeenlaunchedcombiningtheskills and experience of industry and researchexpertiseintheuniversitytodevelopanunderstanding of fully encapsulated rock
5、bolts.Thebroadobjectivebeingtoimprovetheperformanceofrockboltsystemsandhenceimproveoverallsafetyinmines.Thisinitiativeresultedintheestablishmentofa test facility at UNSW that operates within acontrolledlaboratoryenvironment.As part of this initiative,the research aimed toquantifythesensitivitytochan
6、gesinvariousrockboltparameters on anchorage performance.This paperoutlinestheresultsfoundtodatewithregardtothethickness of the resin annulus on anchorageperformanceoffullyencapsulatedrockbolts.TEST FACILITY Design objectives Thedesirableattributesofarockbolttestfacilitywereseenas:thefacilityshouldbe
7、capableofexaminingawiderangeofparametersassociatedwiththeinstallationofrockboltsandofreplicatingawiderangeofconditions;tests should be carried out under controlledconditions to better ensure the repeatability ofresults;thefacilityshouldbeavailableforusebyindustry(bothsuppliersofrockboltsystemsandind
8、ustryendusers)for such purposes as independentlyassessing the performance of new products orchangesinthemethodofinstallation.The design of the new test facility incorporates ahydraulicramsimilartothatusedinmostrockboltpullout tests.The ram can apply various loadconditionstoarockbolt.Abiaxialcellisus
9、edtoholdthe test specimen containing a fully encapsulatedrockbolt.Thetestspecimenmayeitherbeasampleofrockreplicatingtheconditionsinaparticularmineor,amanmadematerial.Theadvantageofthelatterisitmitigatesmanyoftheproblemsthatcanariseduetothe variability in material properties between rocksamples.Theef
10、fectofresinannulusthicknessonanchorageperformanceoffullyencapsulatedrockboltsPCHagan,UNSWMiningResearchCentre2Facility features ThetestfacilityattheUNSWMiningResearchCentreusesamodifiedworkshoplatheasthetestplatform.Themaincomponentsofthefacilityinclude:abiaxialcellwithaninternaldiameterof145mm,leng
11、thof200mmandratedmaximumconfinement pressure of 30MPa mounted to thebedofthelathe;servocontrol hydraulic system used for precisecontrol of the loading rate of a 300kN capacityhollowcoreramduringapullouttest;computerised system to control the applied loadthrough the hydraulic system and monitor theac
12、tualloadanddisplacementoftherockbolt.TEST SAMPLE PREPARATION Test samples Acementitousgrout(CeltiteMG75S)wasselectedinplaceofcoredrocksamplesinthetestprogram.Thestrengthofgroutwasapproximately75MPa.In order to ensure uniform material properties,asingle batch of over 100 test samples was preparedandc
13、astinplasticmoulds.Eachcorehadadiameterof145mmandlengthof200mm.Thesampleswerecuredforatleast28daysbeforetesting.A hole was drilled in each sample to a depth of175mmusingadrillrodmountedonthelathe.Achiselbitwasusedforthe26mmholeandfingerbitswere used for the larger holes.A constant rotationspeedandfe
14、edratewasusedwithwaterflushingtoensureuniformroughnessoftheborehole.Rockbolt anchorage ACeltite24mmextrahighstrengthCXrockboltwasusedinthetestprogramwithabasicprofiledesignasshown in Figure 1.The rockbolt has an inner corediameter of 21.7mm,a diameter across the ribs of22.8mmandribspacingof10mm.Ther
15、ockbolthasanultimatetensilestrengthof344kN.Figure 1.Profile of the rockbolt used in the test program.Resin cartridges were initially used for anchoring,however,problems with poor mixing between theresinandcatalystandwiththeplasticpackagingledto inconsistent results.The poor mixing wasexacerbatedbyth
16、eshortlengthofencapsulation.Amixandpourresinwassubsequentlyusedinthetestprogram.Aftermixing,theresinwasinjectedintothe hole into which the spinning rockbolt wasrammed.The rockbolt was supported in the chuckwhile the resin was allowed to set for 10min.Theresinwasthenlefttocureforafurther48hwiththerockboltandsamplestandingvertically.Itwasobservedthatwiththechangefromacartridgeresintoamixandpourresintherewasaneartwofold increase in the maximum pullout load toapproximately200250kN.EXPERIMENTAL PROGR
