An Integrated Numerical Modelling–

ORIGINALPAPER

AnIntegratedNumericalModelling–DiscreteFractureNetwork

ApproachAppliedtotheCharacterisationofRockMassStrength

ofNaturallyFracturedPillars

DavideElmoÆDougStead

Received:24April2008/Accepted:28November2008/Publishedonline:23January2009

ÓSpringer-Verlag2009

AbstractNaturallyfracturedminepillarsprovidean

excellentexampleoftheimportanceofaccuratelydeter-

miningrockmassstrength.Failureinslenderpillarsis

predominantlycontrolledbynaturallyoccurringdisconti-

nuities,theirinfluencediminishingwithincreasingpillar

width,withwiderpillarsfailingthroughacombinationof

brittleandshearingprocesses.Toaccuratelysimulatethis

behaviourbynumericalmodelling,thecurrentanalysis

incorporatesamorerealisticrepresentationofthe

mechanicalbehaviourofdiscretefracturesystems.This

involvesrealisticsimulationandrepresentationoffracture

networks,eitherasindividualentitiesorasacollective

systemoffracturesets,oracombinationofboth.Byusing

anintegratedfiniteelement/discreteelement–discrete

fracturenetworkapproachitispossibletostudythefailure

ofrockmassesintensionandcompression,alongboth

existingpre-existingfracturesandthroughintactrock

bridges,andincorporatingcomplexkinematicmechanisms.

Theproposedmodellingapproachfullycapturesthe

anisotropicandinhomogeneouseffectsofnaturaljointing

andisconsideredtobemorerealisticthanmethodsrelying

solelyoncontinuumordiscontinuumrepresentation.The

paperconcludeswithadiscussiononthedevelopmentof

syntheticrockmassproperties,withtheintentionofpro-

vidingamorerobustlinkbetweenrockmassstrengthand

rockmassclassificationsystems.KeywordsNumericalmodellingÁRockpillarsÁ

RockmasspropertiesÁRockmasscharacterisationÁ

Discretefracturenetwork

1Introduction

Rockpillarscanbedefinedastheinsiturockbetweentwo

ormoreundergroundopenings.Inthedesignofroom-and-

pillarorstope-and-pillarsystems,theloadingcapacityofa

pillar,i.e.itsstrength,isequallyasimportantasthesta-

bilityoftheroofandwalls(Nordlundetal.1995).Studies

onhardrockpillarsdatebacktothe1970sand1980s.

Importantrecentcontributionstothesubjectincludethose

ofMartinandMaybee(2000),Diederichsetal.(2002),

FangandHarrison(2002)andRobertsetal.(2007).

Figure1illustratestypicalfailuremechanismofanaturally

fracturedpillar,including(a)failurebylateralkinematic

releaseofpreformedblocksduetotheincreasingvertical

load,(b)failureasaresultoftheformationofinclined

shearfracturestransectingthepillar,typicallyinrelative

lowwidth-to-height(W:H)ratiopillarsand(c)failure

alongasetoftransgressivefracturesoccurringiftheangle

ofinclinationofthefracturestothepillarprincipalaxisof

loadingexceedstheirangleoffriction.Overall,the

mechanicalresponseofapillarisdirectlylinkedtothe

presenceofgeologicalstructuresanditcanbesafely

assumedthattheseeffectswouldbemorenoticeablefor

slenderpillars.

Themostgenerallyacceptedtechniquesforestimating

pillarstrength(definedastheultimateloadperunitareaofa

pillar)useempiricalformulaebasedonsurveydatafrom

actualminingconditions(MartinandMaybee2000).

However,empiricalmethodsdonotconsiderspecificfail-

uremechanismsandtheirlimitationsareassociated

withD.Elmo(&)

GolderAssociatesLtd,GreaterVancouverOffice,

Burnaby,BC,Canada

e-mail:Davide_Elmo@golder.com

D.Stead

DepartmentofEarthSciences,

SimonFraserUniversity,Burnaby,BC,Canada

123RockMechRockEng(2010)43:3–19

DOI10.1007/s00603-009-0027-3theirintrinsicderivationfromspecificmaterialproperties

(observedsize,shapeandstressconditions).Numerical

methodsovercomesomeofthelimitsoftheempirical

methodsandprovideanopportunitytoincreaseourfun-

damentalunderstandingofthefactorsgoverningthe

strengthanddeformationalresponseofjointedrockmasses.

Continuumanddiscontinuummodelscanbeutilisedto

simulatemultifracturingphenomenaandthemechanical

behaviourofdiscretesystems.However,neitherapproach

alonecancapturetheinteractionofexistingdiscontinuities

andthecreationofnewfracturesthroughfracturingofthe

intactrockmaterial(CogganandStead2005).Hybrid

modelshavebeenincreasinglyusedinrockengineering,

combiningtheabovemethodsinordertoeliminateunde-

sirablecharacteristicswhileretainingasmanyadvantages

aspossible.ThisisillustratedbyElmo(2006)andPine

etal.(2006)whorecentlyintroducedanewnumerical

modellingapproachfornaturallyfracturedrockmassesthat

combinestherepresentationofexistingrockjointingwith

theuseofaloadingmodelwhichfullyaccountsforthestyle

ofjointing.Thecurrentpaperreviewsthemaincharacter-

isticsoftheaforementionedapproachandpresentsrecent

resultswithspecificemphasisonthecharacterisationof

rockmassstrengthfornaturallyfracturedhard-rockpillars.

Significantcontributionsofthispaperincludeabetter

characterisationoftheanisotropicandinhomogeneous

effectsofnaturaljointingandadiscussiononthedevel-

opmentofso-calledsyntheticrockmassproperties.

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