Damage modeling of saturated rocks in drained and undrained conditions

A new anisotropic damage model is proposed to describe the mechanical and poromechanical behavior of brittle rocks in drained and undrained conditions. Although phenomenological, the model is based on physical grounds of micromechanical analysis. Induced damage is represented by a second rank tensor, which is related to the density and orientation of microcracks. Damage evolution is related to propagation of the microcracks. The effective elastic compliance of the damaged material is obtained from a specific form of the Gibbs free enthalpy function. Irreversible damage-related strain due to residual opening of microcracks after unloading is also captured. The originality of our approach is that a poromechanical model of a saturated medium is constructed by extension of the mechanical model for dry material using micromechanical relationships. All the model parameters are determined from triaxial compression tests performed on dry material. The proposed model is applied to coupled poromechanical tests performed on typical brittle rock in saturated conditions. Comparison between test data and numerical simulations shows overall good agreement. The model proposed is able to describe the main features of poromechanical behavior related to microcracks induced in brittle geomaterials.