Rock mass is heterogeneous, anisotropic and discontinuous. When civil engineering structures like dams are founded on rock, they transmit normal and shear stresses to the joints of the rock mass. For a realistic assessment of the stability of a structure, estimations of the shear resistance of a rock mass both along any desired plane of potential shear and along the weakest discontinuity are essential. To quantify the influence of the rock material and of the roughness on the strength of joints, various researchers have proposed different equations and correlations to estimate strength parameters. This paper briefly describes a new approach to characterize the three-dimensional morphology of rough joint surfaces and proposes a new equation to evaluate the peak shear strength.


The shear strength of rock joints is markedly influenced by the roughness of the joint surface, as well as by the nature of the rock material itself. Since over twenty years, various attempts have been made to quantify these effects. Most of such attempts either relied on experimental testing to derive empirical parameters, or on numerical models based on a discontinuous approach (distinct element codes). The major difficulty in dealing with these latter models appears to be the proper choice of the input data set of parameters (joint stiffness and strength). Patton (1966) quantified the roughness by defining the dilatation angle and developed a theory for the shear strength of rock joints based on such a measure of roughness. Ladanyi & Archambault (1970) developed a model for the shear strength of rock joints, assuming that two modes of failure occur simultaneously. Although the idea behind their model is excellent, it is difficult to determine the parameters used. To determine the JRC Tse & Cruden (1979) converted Barton's table into equations.

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