Development of an orthotropic constitutive model for a jointed rock mass

Fracture data available for a limestone rock mass were used to build and validate a stochastic 3-D fracture network model. A procedure is proposed to investigate the size effect and the REV and equivalent continuum behaviors of fracture and mechanical properties in 3-D of the jointed rock mass having finite size fractures capturing the anisotropic effects arising from the fracture system. An REV size of about 25 m, which is about 8 times the mean fracture size of joint sets, was found to represent the mechanical properties of the rock mass. A number of relations are developed between the rock mass mechanical parameters and fracture tensor components in 3-D. Based on the mechanical parameter values obtained in every 45 degree direction in 3-D, the principal values, principal directions and tensors are developed for rock mass mechanical parameters to represent the REV size properties. An incrementally linear elastic, orthotropic constitutive model is suggested to represent the equivalent continuum pre-failure mechanical behavior of the rock mass by incorporating the effect of fracture geometry by the fracture tensor components.