underground execvations
DESCRIPTION
underground excavationsTRANSCRIPT
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PartIVAnalysisofUndergroundExcavations
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ObjectivesAnalysisanddesignofundergroundmineexcavations Priordeterminationofstabilityproblems
Notnecessarilytopreventdeformationandfailurebuttopreventlarge,uncontrolleddisplacementsandfailurefromoccurringduringexpectedexcavationlife
Stressdistributionnearminingexcavationface Designofsupportsystems
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UndergroundExcavations
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GeneralDescriptionInsitustresses Estimationoffield(insitu)stresses
Materialproperties Materialconstitutivemodel
Supportsystems Rockbolts,shotcrete,steelsets,etc.
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RockMassPropertiesEstimationofYoungsmodulus,E Intactrockstrength GSI(Table)
Rockmassstrength e.g.,HoekBrown mi Intactrockstrength
GSI(Table)
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RockMassPropertiesE =173MPa, =0.3Rockmassstrength=0.3MPa
HoekBrowncriterion
Insitustress=1.35MPa
Strengthtostressratio=0.22
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ApproximateGuidelinesFewstabilityproblems,nosupport
Designbyrocksupportinteraction
Carefulsupportdesign
Seriousstabilityproblems,careful
sequencingrequiredImpossibletosupport
00.17 0.3c p
00.05 0.17c p
00.05c p
00.3 0.5c p
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0.5c p
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StressesatMiningFaceRedistributionofstressesduetoexcavation
3Dflowofstressesaroundadvancingface
Tunnel advancement
Tunnel displacement
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Support installation
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3DFaceStressDistributionExamine3D modelofdrift
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ProfileofTunnelDisplacements
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ConvergenceConfinementMethodConvergenceConfinementMethod(CCM) 2Dapproach Reasonablyestimatestunneldeformationspriortosupportinstallation Estimatesloadsimposedonsupportsystemsinstalledaroundtunnels
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ConvergenceConfinementMethodIdealizedconditions Circulartunnel Hydrostaticinsitu stressstate
Comprisesthreebasicparts LongitudinalDeformationProfile(LDP) GroundReaction/ResponseCurve(GRC) SupportCharacteristicCurve(SCC)
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Whyuse2Danalysisfor3Dproblem?Fewexisting3Dsupportmodelling tools
Absenceofmeshalgorithmforarbitrary3Dgeometries
2D relativelysimpleapproach Givesreasonablygoodresults
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ConstructionofLDPVariousmethods Panet Chern Vlachopoulos &Diederichs Axisymmetric FEManalysis
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ExampleLDP Chern Equation
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ExampleLDP Chern Equation
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GroundReactionCurve(GRC)Relatesradialdisplacementoftunnelwallstointernalpressureactingontunnelwalls
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GroundReactionCurve(GRC)Generation Elastoplasticsolutionsofdeformationaroundexcavation Numericalanalysis(Phase2) twomethods Supportpressure:progressivelyreducesurfacepressure(Panet,1982) Materialsoftening(coresoftening):progressivelyreducemodulusofdeformation,E(Swobada,1979)
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SupportPressureApproachAdvancing Tunnel
r r r
r = (1-)o
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SupportPressureApproachCharacteristicline(Groundreactioncurve) Crownandsidewall
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Displacement
Crown
Side wall
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MaterialSofteningApproach
Advancing Tunnel
EE
Stiffness reduction factor
Initial stage stage 1 stage 2 Final stage
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SupportPressureApproachStagedmodellingofinternalpressure
Useoffieldstressvectordistributedloadplusstagedfactors
Plotofradialdisplacementsagainststages
PlotofGRCinExcel
Identificationofmaximumradialdisplacementandradiusofplasticzone
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ExampleofGRC
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Tunnel Convergence (%)
Ground Reaction Curve
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CreationofLDP
Requires Distancefromfaceatwhichsupportisinstalled Maximumtunneldisplacement Radiusofplasticzone Tunnelradius Radialdisplacementattunnelface
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CreationofLDPEssenceofVlachopoulos andDiederichs approach LDPdependsonsizeofplasticzonearoundtunnel
Equations
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CreationofLDP
Step1:calculatePr
Step2:calculateratiouo/uMaxStep3:calculateuoStep4:plotratioofwalldisplacementstomaximumradialdisplacementasfunctionofdt wheredt =X/Rt , X isthedistantfromthetunnelfaceandRt isthetunnelradius
Step5:determinetunnelconvergenceattimeofsupportinstallation
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SupportCharacteristicCurve(SCC)Relatespressureonsupporttoradialdisplacementsoftunnelwall
Hoek &Brown(1980)tables/equations provide YoungsmodulusKs ofsupportsystem(compositeofconcreteandsteelmember)
Maximumcapacityofsupport
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SupportStiffness&Capacity
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ExampleofSCC
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Tunnel Convergence (%)
Support Characteristic Curve
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AlgorithmforCCMStep1:determineLDP(Vlachopoulos &Diederichs)
Step2:fromdistanceofsupportinstallation,L,andLDPdeterminetunnelradialdisplacement,us,attimeofsupportinstallation
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AlgorithmforCCM
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AlgorithmforCCM
Step3:onplotofGRC,placeSSC(startingatus)
Step4:determineintersectionofGRCandSCC thisgivesestimateoffinalloadactingonsupport(equilibriumconditions)
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SchematicDrawingofCCMTwocurves GRC SCC
Factorofsafety
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FinalConvergence&FS
FS =pimax forsupport/pi atequilibriumconditionNUMERICAL MODELLING IN ROCK
ENGINEERING
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GeneralizedSupportDesignRevisitPhase2modelforcreatinggroundreactioncurve
Modify includestagefactorthatgivesconvergenceattimewhensupportisinstalled
Compute
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GeneralizedSupportDesign
PlotSupportCapacityCurvesforrequiredfactorofsafety Alsoshowswhereactualsupportloadsarerelativetosupportcapacityenvelope
Ifactualsupportloadsliewithinenvelopesupportisadequate Ifnotthenincreasesupportstrength
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SupportCapacityPlotsforLinerPlotSupportCapacityCurvesforgivenliner
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SupportDesign ExampleV1Tutorial Tunnelinweakrock Simulationof3D
facebehaviour Surfacesettlement Applicationofliner
support Materialsoftening
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MaterialSofteningMaterialsofteningratio, =(0,1)
Surfacesettlement
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0 1 2 3 4 5 6 7Settlement (mm)
1-Youngs modulus of Softened Soil (kPa)
0.1180,000
0.4120,000
0.680,000
0.840,000
0.920,000
0.9510,000
0.9755,000
0.9951,000
0.9975500
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SupportInstallationInstallsupportatspecifiedsettlement Softensystem(byspecified)atStage1 AddlineratStage2
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ContoursofTotalDisplacement
Stage1(softenedmaterial) Stage2(installedsupport)
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ForcesinLinerSupport
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EndofPartIV
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