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Text of © Copyright 2012, Australian Centre for Geomechanics (ACG), The

  • Copyright2012,AustralianCentreforGeomechanics(ACG),TheUniversityofWesternAustralia.Allrightsreserved.NopartofanyACGpublicationmaybereproduced,storedortransmittedinanyformwithoutthepriorwrittenpermissionoftheACG.

    ThefollowingpaperappearedintheDeepMining2012proceedingspublishedbytheAustralianCentreforGeomechanics.

    AuthorsofthepapersandthirdpartiesmustobtainwrittenpermissionfromtheACGtopublishallorpartofthesepapersinfutureworks.Suitableacknowledgementtotheoriginalsourceofpublicationmustbeincluded.

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    DeepMining2012Y.Potvin(ed)2012AustralianCentreforGeomechanics,Perth,ISBN9780980615487

    DeepMining2012,Perth,Australia 1

    Progress and challenges in some areas of deep mining

    E.T.BrownGolderAssociatesPtyLtd,Australia

    Abstract DeepMining2012 is thesixth inaseriesof internationalseminarsondeepandhighstressminingwhichbeganwithaseminarheldinPerthinNovember2002,almostadecadeago.Theearlyannouncementsforthisseminarlistedtenseminarthemes.Thispaperseekstomakecontributionstothediscussionofprogressmade in four of these themes geomechanics risks, risk assessment andmanagement, rock behaviourunderhighstress,andnumericalmodellinglargely,butnotonly,throughareviewofthepaperspublishedintheproceedingsofthefivepreviousseminars.Particularemphasisisplacedontherisksassociatedwiththenewgenerationofblockandpanelcavingoperationsorsupercaves.Someremainingchallenges inthefourthemeareasdiscussedarealsoidentified.

    1 Introduction DeepMining2012 isthesixth inaseriesof internationalseminarsondeepandhighstressminingwhichbeganwithaseminarheldinPerthinNovember2002,almostadecadeago.Thewriterhasnotattended,orcontributedto,anyofthefivepreviousseminarsinthisseries,andsoapproachesthetaskofpreparingthiskeynotepaperfromtheperspectiveofanewcomertotheseDeepandHighStressMiningseminars.

    Theearlyannouncements for this seminar listed10 seminar themes:geomechanics risks, financial risks,casestudies,numericalmodelling,rockbehaviourunderhighstress,rockburstandseismicitymonitoring,ground support, risk assessment andmanagement, ventilation, and blasting. This paper seeks tomakecontributions to the discussion of progress made in four of these themes: geomechanics risks, riskassessmentandmanagement,rockbehaviourunderhighstress,andnumericalmodellinglargely,butnotonly, through a reviewof thepaperspublished in theproceedingsof the fiveprevious seminars. Someremaining challenges in theseareasarealso identified.For the reasons tobeoutlined inSection2, thispaperwillconsidersomemethodsofdeepandhighstressminingmorethanothers.

    2 Deep and high stress mining methods The papers presented to the previous seminars have dealtwith awide range of generic undergroundminingmethods,including:

    deeptabularorebodymining(includinglongwallmethods,remnantminingandtheminingofshaftpillars)

    longwallcoalmining

    blockandpanelcaving

    sublevelcaving

    underhandandoverhandcutandfillanddriftandfillstoping

    benchandfillstoping

    sublevelandlongholeopenstoping(includingnarrowveinmethodssuchaslongholeretreatorAvocaandmodifiedAvocamethods)

    roomandpillarmining

    variantsofthesemethods,includingtheiruseinpillarrecoveryandsillpillarmining.

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    Progressandchallengesinsomeareasofdeepmining E.T.Brown

    2 DeepMining2012,Perth,Australia

    Overa longcareer,thewriterhashadsomeassociationwithminesusingallofthesemethods.However,during the 10 years inwhich the seminar series has been in operation, hismajormining interest andexperience has been in block and panel caving (Brown, 2007a, 2007b). He also has a longstandingassociationwithmetalliferousminingbydriftandfillandbenchandfillmethods(Beenetal.,2002;Brown,1999). The observations drawn from the writers own experience will dealmainly with theseminingmethods.Any reference tootherminingmethods,particularly theminingofdeep, tabularorebodies inSouthAfrica,willbethroughreferencetopaperspublished intheproceedingsofthisseminarseriesandelsewhere.

    3 Geomechanics risks

    3.1 Definitions Thefirstquestiontobeansweredishowdowedefineageomechanicsrisk?Theliteratureonriskanalysis,assessment andmanagement contains a range of definitions of risk and associated terms. Here, thedefinitionsgivenbyAS/NZS ISO31000:2009 (StandardsAustralia,2009)willbeused. Itshouldbenotedthatthesedefinitionsdiffer,sometimesmarginallyandsometimessignificantly, fromthoseused insomeearlierpublications,includingthosebythewriter(Brown,2007a;BrownandBooth,2009;Summers,2000).StandardsAustralia(2009)definesriskastheeffectofuncertaintyonobjectivesandarisksourceasanelementwhichaloneorincombinationhasthepotentialtogiverisetoarisk.Insomeearlieraccounts,arisksourceappearstohavebeenreferredtoasahazard,definedinthepreviousAustralianStandardasasourceofpotentialharm(StandardsAustralia,2004).ThistermisnotdefinedinAS/NZSISO31000:2009.The levelofrisk isdefinedasthemagnitudeofariskorcombinationofrisks,expressed intermsofthecombinationofconsequencesandtheir likelihood.Thisdefinitionallowsforthecommonpractice intheminingindustryandelsewhereofquantifyingriskastheproductofthelikelihoodoftheoccurrenceofaneventand theconsequencesof thatevent (Brown,2007a;BrownandBooth,2009;Steffenetal.,2008).TheStandardsAustralia (2009)definitionofaneventasan occurrenceor changeofaparticular setofcircumstances is consistentwith thisusage.The consequenceofanevent is the outcomeofaneventaffectingobjectivesandlikelihoodisthechancethatsomethingwillhappen(StandardsAustralia,2009).

    AriskevaluationprocessasappliedtostopedesignisshowninFigure1.ThelefthandcolumnofFigure1identifiespossiblecausesofstope failure. It issuggested that, in termsof theStandardsAustralia (2009)definitions, these occurrences are best described as events. Following an approach that is commonlyadopted in themining industry (Steffenet al.,2006;Tapiaet al.,2007), in the central column risks arecategorised in terms of consequences as being expected fatalities, expected economic loss, loss ofproduction, probability of forcemajeure, industrial action and stakeholder resistance. The right handcolumninFigure1isconcernedwiththelevelofriskasdefinedbyStandardsAustralia(2009).Thequestionthenremainsastowhatwemeanbyageomechanicsrisk.Forpresentpurposes,andforconsistencywiththeterminologyusedinAS/NZSISO31000:2009,ageomechanicsriskwillbetakentobeageomechanicsrelated risk source, hazard or uncertainty that gives rise to events of the types listed in the lefthandcolumn of Figure 1, not only in stopes but in other underground mining excavations as well. Thisdefinitionwillbeinterpretedratherliberallyinthatwhichfollows.

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    KeynoteAddress

    DeepMining2012,Perth,Australia 3

    Figure 1 Risk evaluation process (Stacey et al., 2006)

    3.2 Generic geomechanics risks in deep and high stress mining Thenatureoftheuncertaintyandtheerrorsthatprovidethesourcesofgeomechanicsriskingeotechnicalengineeringmorebroadlyhavebeendiscussedwidelyintheliterature.Forexample,EinsteinandBaecher(1983)classifiedthesourcesofuncertaintyas:

    inherentspatialandtemporalvariability

    measurementerrors(systematicorrandom)

    modeluncertainty

    loaduncertainty

    omissions.

    Baecher andChristian (2003)described these sourcesofuncertainty asbeing aleatory (randomness)orepistemic (lack of knowledge). Similarly, in discussing variability in soil properties, Phoon and Kulhawy(1999) suggested that thereare threeprimary sourcesofgeotechnicaluncertainty inherentvariability,measurementerror,andtransformation(ormodel)uncertainty.Indiscussingriskinageneralengineeringcontext,incommonwithBaecherandChristian(2003)andothers,Brown(2007a)concludedthattherearetwogeneraltypesofuncertainty:

    whatweknowwedontknow,orparameteruncertainty;and

    whatwedontknowwedontknow,orconceptualuncertainty.

    Recently,HadjigeorgiouandHarrison(2011)providedavaluableaccountofuncertaintyandthesourcesoferror in rock engineering. In discussing the use of rock mass classification schemes in the design ofundergroundexcavationsthey identifytwogroupsoferrors.Thefirstgroupconsistsoferrors intrinsictothe classification scheme used, including errors of omission, errors of superfluousness, and errors oftaxonomy associated with the requirement to select a particular classification rating value for ageomechanical property. The second group of errors are associatedwith implementation, and include

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    Progressandchallengesinsomeareasofdeepmining E.T.Brown

    4 DeepMining2012,Perth,Australia

    errors of circumstance, errors of convenience, errors of ignoring variability, and errors of ignoringuncertainty.

    Clearly,deepandhigh stressmining is susceptible to thegeomechanics risksorhazardsassociatedwithuncertaintiesanderrorsoftheseseveraltypes,aswellastoothercategoriesofrisk(SweeneyandScoble,2006).Itshouldbepossibletodevelopadetailed(ifnotcomprehensive) listoftheserisksorhazardsandtheir sources similar to that developed for open pit slopes by Brown and Booth (2009)who identifiedgeology, structure, rockmass, hydrogeology and geotechnicalmodel hazards or risks. In discussing themanagementofgeotechnicalrisksinminingprojects,Hebblewhite(2003)suggestedthattheriskswithinaminingoperationcanbecategorisedasoccupyingthreelevelsorsuperimposedlayers:

    Level1daytodayoperationalrisksmanagedthroughmechanismssuchastrainingandSafeOperatingProcedures.

    Level2specificsiteorminingcond