The deformation and failure process of coal rock under different strain rates is a significant challenge which must be solved in dynamic excavation. It is important to study the influence of strain rate on the evolution of coal rock crack. The triaxial compression tests and acoustic emission tests under the strain rate of 10−5 s−1 to 10−3 s−1 were conducted on coal rock using MTS 815 hydraulic servo-control testing machine. During the loading process, acoustic emission energy and spatial distribution have obvious stage characteristics. The damage variable is defined by acoustic emission energy, and the rate of damage evolution is obviously affected by the strain rate. Based on stage characteristics of acoustic emission energy, spatial distribution, and damage evolution, the use of damage evolution curve to determine stress threshold is proposed. In order to verify the rationality of the damage evolution method, the stress threshold values determined by damage evolution method and existing method are compared and analyzed. In order to study the effect of strain rate and confining pressure on the stress threshold, the stress thresholds under uniaxial and triaxial stress states at different strain rates were analyzed.

The study on the mechanical response of deep rock under hydromechanical couplings condition can guide the safe excavation and stability evaluation of deep tunnel engineering. The effects of monotonic loading and cyclic loading on the mechanical properties of granite under 5 MPa pore water pressure and 10 MPa confining pressure were studied by laboratory tests. Before the peak stress, the permeability under monotonic loading was significantly higher than that under cyclic loading, and the permeability under cyclic loading increased sharply after the peak stress. There were two active periods of the acoustic emission energy before peak stress under monotonic loading, but it was always in relative quiet period under cyclic loading before peak stress. Based on the energy theory, the energy evolution of granite was discussed. The dissipation energy can better reflect the effect of loading mode on the energy evolution.

In order to study the laws of crack evolution in rock and explain its fracture instability mechanism, a series of laboratory tests were carried out with Jinping Marbles. The test results show that the failure degree of marbles under unloading conditions is more severe than that under loading conditions. Based on volume crack strain, five progressive failure stages of crack evolution under different conditions are divided, and the corresponding characteristic stresses are determined. The pre-peak volume crack propagation strain without considering the initial damage is used to evaluate the pre-peak crack growth propagation degree of rock, and it is found that the lower the confining pressure, the higher the strain rate and unloading rate, the less the cracks generated before the peak, and the more the rock is prone to brittle failure after the peak. The starting point of the sharp increase of volume crack strain rate is proposed as the failure precursor point, and stress levels of failure precursor of marbles are in 70%–100%, which decrease as confining pressure, strain rate, and unloading rate rise. Under unloading conditions, failure precursor points appear later and are close to the unloading point, and unloading rocks are more prone to sudden brittle failure.