Damage and Energy Evolution Characteristics of Granite under Triaxial Stress

In order to reveal the mechanical properties and energy evolution of hard rock under different confining pressures, conventional triaxial compression tests on granite samples under different confining pressures were carried out by the RMT-150B rock mechanics test system. The results showed that the peak stress of the rock sample had a strong linear relationship with the confining pressure. The cohesive force of the granite was 23.548 MPa and the internal friction angle was 57.629° using the Mohr-Coulomb strength criterion. The peak energy, elastic strain energy and dissipation energy of the rock all increased linearly with the increase of confining pressure. According to the linear energy storage law of the rock, a method to determine the rock threshold stress was proposed, the greater the confining pressure, the larger of cracking stress and expansion stress, the larger the energy at the initiation point and the expansion point of the rock sample. When the confining pressure is low, there existed less energy stored in the rock before failure, the energy release rate is low, and the rock sample shows typical splitting failure. Under high confining pressure, the energy gets released rapidly, and the rock sample shows shear failure. Besides, a rock damage evolution model was proposed based on the law of energy evolution, and the law of evolution of damage variable D on the granite was obtained during loading failure under different confining pressures.