ABSTRACTA numerical method, the displacement discontinuitymethod, has been reformulated and computerized toprovide a practically applicable method for comprehensiveanalysis of rock masses. In particular, stiffnessrelationships have been incorporated to describecomprehensively the history-related behavior of rockdiscontinuities. The method has been successfullyapplied in the analysis of fracture propagation throughloaded wedge of intact rock.INTRODUCTIONThe behavior of rock masses is usually governedby the geometry and behavior of discontinuities.The effect of discontinuities can only be fully understoodand analyzed if their history is taken intoconsideration. By determining and analytically describingthe behavior of individual discontinuitiesfrom their creation to the present state it becomespossible to better predict their subsequent behavior.This paper describes a model that is capableof providing such an analytical description and thenillustrates the model in an application.DISPLACEMENT DISCONTINUITY METHOD (DDM)Various numerical techniques are available tomodel the behavior of a discontinuous rock mass. Themethod chosen and described here is the DisplacementDiscontinuity Method (DDM), which is an influencefunction technique, similar to boundary element orboundary (J) integral methods. Such methods have beendeveloped and applied by various researchers(Ronvedand Fraser (1958), Hackett (1959), Berry (1960), Bilby(1960), Weertman (1964), Massonet (1965), Rizzo (1967),Cruse (1969), Benjumea and Sikarskie (1972), Diestet al (1973), Thompson (1974), Crouch (1976), Lachat andWilson (1976), Brady and Bray (1978),Roberds (1979),Among others). The DDM incorporates the ability toadequately model rock masses as a quasicontinua similarto finite element techniques, without either the highcost or imposition of often artificial boundariesinherent in finite element modelling.Analysis by DDM essentially entails therepresentation of a problem as surfaces of displacementdiscontinuity within an infinite and otherwisecontinuous body (Fig. 1a).

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