In this chapter alternative formulations to consider directionally orientated material weaknesses and slip or separation along discontinuities for rocks are presented. The chapter starts by introducing a model to study weakness in a particular direction within the context of continuum mechanics. In many schistous rock materials, shear and tensile strengths respectively parallel and orthogonal to schistosity are zero or very small in comparison to those of intact rocks (103). In order to model such material weaknesses the shear strength parallel to the schistosity is assumed to be governed by a simple Coulomb criterion of failure. Also the tensile stress in the direction orthogonal to the schistosity plane can be limited by the tensile strength value which is usually assumed to be zero.
KeywordsShear Strength Intact Rock Stress Vector Discontinuity Surface Joint Element
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