Micromechanical Modeling and Simulation of Instantaneous and Long-Term Behaviors of Red Sandstone under Lateral Unloading Conditions

This paper is devoted to presenting a micromechanical model for describing instantaneous and long-term mechanical behaviors of typical quasi-brittle rocks under lateral unloading conditions. The unified damage-friction coupling model is formulated in a combined linear homogenization and irreversible thermodynamics framework. Crack propagation and friction sliding are regarded as the two primary dissipation and coupling mechanisms, respectively related to material damage and plastic deformation. Rock damage due to microcracking is divided into two parts: an instantaneous part induced by variation in stresses and a time-dependent part caused by subcritical extension of microcracks due to stress corrosion. Both the instantaneous and long-term mechanical behaviors of rock are taken into account in a unified way, which closely resemble the excavation scenarios encountered in practical engineering. In addition, we conduct a series of experiments under unloading conditions to provide experimental data for model validation and analytical predictions.