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1、TobepublishedinReportontheWorkshoponExtremeGroundMotionsatYuccaMountain(U.S.GeologicalSurvey,MenloPark,California,August23-24,2004).FUNDAMENTALCONSIDERATIONSRELATINGTOTHESTRENGTHOFROCK*CharlesFairhurst**1.0THESTRENGTHOFROCKWhethertheaimbetopreventcollapseortopromot
2、eit,rockstrengthisanimportantfactorinmanypracticalproblemsofrockmechanics.Thepropertyof‘strength’ofarockderives,aswithallsolids,fromvarioustypesofinter-atomicandintermolecularbonds,somestrongandothersrelativelyweak,thatexistwithintherock.Tobreaktherock,itisnecessar
3、ytobreakenoughbondstoseparateitintoatleasttwopieces.Abondbetweenapairofatoms(ormolecules)isformedasaresultoftwoforces—oneanattraction,theotherarepulsion.Theforce-intensityversusatomic-separationrelationshipdiffersforthetwoforcessuchthattheresultantforcebetweentheat
4、om-pairforvariousspacingsisasshowninFigure1.Figure1Schematicrepresentationof(i)forces;(ii)potentialenergytroughbetweenatoms(afterHouwink,1958p.23)*OriginallypresentedattheColloquiumonRockFracture,RuhrUniversity,Bochum,Germany,April1971,(andrevisedfromoriginal,publi
5、shedinVer?ff.Inst.BodenmechanikundFelsmechanik(Karlsruhe),55,1-56.)**Now(2004)ProfessorEmeritus,UniversityofMinnesota;SeniorConsultant,ItascaConsultingGroup,Inc.,111,ThirdAvenueSouth,Suite450,Minneapolis,MN55401,USA.[E-mailfairh001@umn.edu]FundamentalConsiderations
6、RelatingtotheStrengthofRock2Bothforcesincreaseastheinter-atomicspacingisreduced,withthecompressive(i.e.,repulsion)forcebecomingverydominantatsmallspacings.ThevalueoftheexponentsmandninFigure1varydependingonthenatureofthebondsothattheforceandspacingscaleswillchange,
7、butthegeneralshapeofthenet-forcevs.spacingcurveremainsthesame—i.e.,thereisalwaysatensileorcohesivelimit,adecreaseinnetforceatlargespacing,andarapidincreasewithoutlimitatsmallspacings.Applicationofexternalcompressionforceswillreducetheinter-atomicspacing(i.e.,causet
8、hesolidtocontract)inaccordancewiththenetforce-spacingrelationship;applicationofexternaltensionwillincreasethespacing.Releasetheexternalloadsandth
