Estimating Elastic Constants and Strength of Discontinuous Rock

Abstract

Methods used to estimate strength and deformability properties of discontinuous rock can be categorized into: (1) The direct testing method; (2) the empirical correlation method; and (3) the analytical decomposition model method. In this paper, a numerical method that combines analytical decomposition modeling with statistical simulation is presented. The method consists of: (1) Probabilistic modeling of discontinuity geometry; (2) generation of discontinuities in rock blocks by Monte‐Carlo simulation; and (3) finite element analysis of simulated rock blocks. Strength and deformability properties of intact rock and discontinuities are needed for the finite element analysis. Results of finite element analysis can be used to obtain statistical properties of the rock mass. The method was used to study the mass properties of a shale that contains slickensides. At a block size of 30 in. X 30 in. (25 cm), the mean value of the ratio between shale mass strength and intact shale strength was found to be about 0.6. For the same block size the mean value of the ratio between shale mass modulus and intact shale modulus was found to be around 0.45. At the same block size, Poisson's ratio of shale mass was found to be about two times the Poisson's ratio of intact shale. For ten simulations, the coefficient of variations of all three mass parameters were found to be less than 0.21.