Micromechanical modelling of short- and long-term behavior of saturated quasi-brittle rocks

Abstract This paper presents a physically-motivated micromechanical damage model for describing short- and long-term behaviors of saturated quasi-brittle rocks under drained condition. Rocks are considered composed of a pores-weakened elastic solid matrix and distributed microcracks. The system free energy is determined with the Mori-Tanaka homogenization method. Two main dissipative mechanisms, inelastic deformation due to frictional sliding and damage by crack propagation, are involved and strongly coupled in both stress-loading phases and creep phases under constant stresses. The effect of pore pressure is taken into account in the damage-friction coupling context. The microcracks induced rock damage is divided into two parts: instantaneous damage related directly to stress-induced microcrack growth, and time-dependent damage caused by subcritical cracking. The short- and long-term strengths of saturated brittle rocks are analytically deduced by damage-friction coupling analysis. By using the long-term strength, the creep parameter is calibrated in terms of a critical stress state identified in experiment. Comparisons between model’s predictions and laboratory tests are performed for two typical quasi-brittle rocks under triaxial compression tests and triaxial compression creep tests. It is shown that the proposed model can capture the main features of the mechanical behavior of quasi-brittle materials.