Determination of rock mass strength properties by homogenization

A method for determining fractured rock mass properties is presented here o n the basis of homogenization approach. The rock mass is considered to be a heterogeneous medium composed of intact rock and of fractures. Its constit utive model is studied numerically using finite element method and assimila ting the fractures to joint elements (Coste, Comportement Thermo-Hydro-Meca nique des massifs rocheux fractures These de Doctorat, Ecole Nationale des Ponts et Chaussees, Paris, 1997). The method has been applied to a granite formation in France. Geological data on different families of fractures hav e been used for the statistical representation of the fractures. A mesh-gen erating tool for the medium with high density of fractures has been develop ed. The mechanical behaviour of the rock mass (elasticity, ultimate strengt h and hardening law) has been determined assuming linear elasticity and Moh r-Coulomb strength criterion both for the intact rock and the fractures. Ev olution of the mechanical strength in different directions has been determi ned as a function of the mean stress, thanks to various numerical simulatio ns. The mechanical strength appears to be anisotropic due to the preferenti al orientation of the fractures. The numerical results allowed us to determ ine an oriented strength criterion for the homogenized rock mass. A 2D cons titutive law for the homogenized medium has been deduced from numerical dat a. A 3D extension of this model is also presented. Copyright (C) 2001 John Wiley & Sons, Ltd.