The numerical representation of a rock mass comprised of intact rock and discontinuities truly simulates the characteristics of a real rock mass. This is ensured by mimicking the properties of intact rock, the distribution of joints and by mechanical capture of the joint properties through modeling a rock mass with PFC in the following manner. Generation of PFC assembly that behaves mechanically the same as that of an intact rock sample in the laboratory. By avoiding using a hypothetical constitutive model for intact rock which the finite element method normally does, PFC uses the micro-parameters to create a particle assembly that exhibits the same deformational behavior as an intact rock sample in a compression test and shear test. This excludes inaccuracy of the stress-strain relation hypothesis. The match of deformability in the biaxial and Brazilian tests maximizes the similarity of the numerical representation to a real intact rock. Placing joints into the particle assembly in such a way that the distribution of joints is approximately the same as the discontinuities existing in a real rock mass. The joints placed in the assembly behave the same as a real joint in a shear test. The modeling methods and procedures presented here demonstrate a new approach to the simulation of a rock mass and the stability analysis of excavations in a rock mass. With this new approach, study of the stability of excavations can be carried out in such a way that the development and movement of the rock mass and failure surface can be visualized. With the understanding of where the failure will start, how it develops and what the final failure looks like, a more relevant strategy such as reinforcing the rock to stop the failure at its inception-can be studied and appropriate measures can be taken. PFC's capability of providing full insight into the thorough process of rock mass destabilization is a particular advantage over conventional FEM which, as conventionally used, only indicates final results with no interim results during the failure process. The modeling of rock slope stability and failure reveals that the failure scale and failure mode of a slope of heavily joint rock are dominated by the joint quantity and quality in addition to the intact rock properties. For a given intact rock with certain mechanical properties, joints (discontinuities) play a determinant role in slope stability. In general, for slopes having the same intact rock and joints properties, densely distributed joints result in slope failure on a larger scale than for relatively sparsely distributed joints. A slope with the same intact rock and joint properties may remain stable, depending on the joint density (number of joint sets, spacing and joint persistence). The failure mode of a slope in heavily jointed rock is a result of the joint quantity. Different joint densities result in different failure modes of a slope: a high joint density causes a slope to fail in a sliding mode; whereas, a lesser joint density leads a slope to fail in a combination of multiple failure modes. Although this study is focused on joint persistence, slope stability as a function of other joint parameters can be carried out in the same way.
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