Modeling of periodic elastic strain energy change and failure process of rock specimen with random imperfections in biaxial compression

The mechanical behavior and failure process of a rock specimen with the initially random material imperfections in biaxial compression are modeled using FLAC. Two FISH functions written are adopted to prescribe the imperfections and to calculate the elastic strain energy decrease of all elements per 10 timesteps. For intact rock exhibiting linear strain-softening behavior beyond the failure and then ideal plastic behavior, the failure criterion is a composite Mohr-Coulomb criterion with tension cut-off Imperfection undergoes ideal plastic behavior beyond the failure. The failure process of the specimen in three typical periods with remarkable stress drops is discussed. Periodic elastic strain energy change and stress fluctuation are observed. The elastic strain energy decrease rate reaches its peak in strain-softening stage. In period 1, two shear wedges are progressively formed, surrounding the seismic gap where the earthquake swarm is inactive. In period 2, a shear band appears in the gap and the earthquake activities migrate outwards. The earthquakes belong to rupture type. In period 3, the earthquakes belong to compound type. After that, a longer shear band bisecting the specimen leads to a decrease in the specimen load-carrying capacity.