Numerical investigation on the mechanical and fracture behaviors of marble under cyclic loading and unloading true triaxial compression using discrete element method

The deep-buried rock is subjected to true triaxial stress states and is affected by repeated disturbance loads. The discrete element method was employed to investigate the mechanical behavior and fracture mechanism of marble under true triaxial cyclic loading and unloading. The particle-based marble model with the calibrated microparameters was established based on true triaxial compression. The true triaxial cyclic loading and unloading simulations with different stress states were conducted. The increase in intermediate principal stress results in significant deformation anisotropy. The brittle–ductile transformation characteristics are presented with the increase in minimum principal stress. The crack damage stress initially increases and subsequently decreases with the increase of equivalent plastic strain under different stress states. The plastic strain increments ratios exhibit prominent nonlinear variation during the progressive failure. The rock strength presents the asymmetric distribution by the effect of intermediate principal stress, and the minimum principal stress has an enhancing effect on strength. With the increase in intermediate principal stress or the decrease in minimum principal stress, that is, the effect of high differential stress, the failure plane changes from inclined to parallel to the direction of maximum principal stress. The microcrack numbers present the S-shaped increasing trend during the progressive failure. The increasing number of microcracks parallel to the direction of intermediate principal stress and the anisotropy of microcrack tendency are subjected to high differential stress.