Deformability of intact rock

Abstract

Abstract A constitutive model is presented which uses elasticity, plasticity and continuum damage mechanics to describe the incremental stiffness of rock under general loading paths. Rock strength and elastic deformability are described in terms of a transformed stress tensor, using a continuum damage variable to account for the effect of microcracks on the capacity of rock to support distortional loading. The growth of damage is modelled using an incremental evolution law, which describes the effects of confinement and distortional load intensity on the potential of rock to undergo cracking. The dilation ratio predicted by a plasticity-based material model is determined exclusively by the flow rule; such that an appropriate plastic potential can be obtained by requiring the flow rule to satisfy the measured dilation response. It is argued that functions which satisfy this requirement of geologic materials cannot also predict their strength correctly, which implies that the flow rule has to be non-associative. This approach is applied to describe the inelastic deformability of rock. The material properties required in the model are tensile strength, elastic stiffness, shear resistance and dilation ratio. The last three vary with deformation and confinement. The evaluation of these properties is illustrated using cylindrical triaxial test data.