<p>This work is devoted to modeling time-dependent mechanical behavior for a wide family of rocks. A micromechanics-based approach is adopted and combined with an irreversible thermodynamics framework. Rocks are considered as a heterogeneous material composed of a solid matrix and randomly distributed microcracks. Two fundamental physical mechanisms contributing to the time-dependent behavior of rocks are taken into account including viscoplastic deformation of solid matrix and sub-critical propagation of microcracks. Moreover, the growth of and frictional sliding along closed microcracks are taken into account and coupled. A specific identification procedure of the model’s parameters is proposed. The developed model is used for the description of both short and long-term responses of two typical rocks. It is found that under low confining pressures, the sub-critical propagation of microcracks is the key mechanism of time-dependent deformation. The viscoplastic deformation becomes indispensable when the confining stress is higher. The interaction between the viscoplastic deformation and microcrack propagation allows a better description of the pressure-dependent behavior of rocks.</p>