Meso-energy evolution and rock burst proneness of the stress thresholds of granite under triaxial cyclic loading and unloading test

To study the meso-energy evolution of Sanshandao granite under triaxial cyclic loading and unloading, the stress thresholds (the crack initiation stress σ_ci, crack damage stress σ_cd, and peak stress σ_f) of Sanshandao granite were determined; the variation law of the boundary energy, strain energy (linear contact strain energy and parallel bond strain energy), dissipation energy (friction energy and damping energy), and kinetic energy corresponding to each stress threshold with confining pressures was analyzed; and a new index W_x for evaluating the rock burst proneness was established from the perspective of energy based on a simulation using PFC3D. The results show that the corresponding σ_ci/σ_f is in the range of 37.0% to 44.8%, and σ_cd/σ_f is in the range of 81.2% to 89.0% under different confining pressures. With the increase of confining pressure, the boundary energy, strain energy, and dissipation energy of the crack initiation increase linearly, and the boundary energy, strain energy, and dissipation energy of the crack damage and peak increase exponentially. Among them, the dissipation energy exhibits the maximum increment with the change in confining pressure, followed by the boundary energy, and then the strain energy. The confining pressure has little effect on the proportion of the strain energy of crack initiation. Moreover, with increasing pressure, the proportion of the crack damage and the peak strain energy decrease slowly; however, the proportion of peak strain energy decreases to a greater extent. According to the new index W_x for the evaluation of the rock burst proneness, when the confining pressure was less than 20 MPa, the rock burst proneness of Sanshandao granite was relatively small, and when the confining pressure reached 30 MPa, the rock burst proneness began to increase rapidly. This study provides a new reference index for the evaluation of rock burst proneness and further provides a new idea for the stability study of underground rock mass engineering.