Influence of mine earthquake on the mechanics and seepage characteristics of gas-bearing coal

Frequent occurrence of mine earthquakes poses a serious threat to coal mine safety production. According to the investigation, it is easy to cause gas disasters after the mine earthquake, showing the characteristics of “earthquake first and disaster later”, which provides the possibility of early warning of gas disasters under the action of mine earthquake. However, the seepage law of gas disasters induced by mine earthquake is not clear. Considering the stress environment of coal body and the occurrence principle of gas disaster, based on the analysis of mine earthquake waveform characteristics, a self-designed dynamic triaxial loading seepage test system was adopted, and cyclic stress ratio (CSR) was introduced to simulate the characteristics of mine earthquake. At the same time, the dynamic load frequency and gas adsorption pressure were considered. The dynamic and static combined loading scheme was designed, and the mechanical, microscopic pore and seepage characteristics of gas-bearing coal samples under dynamic load were studied. The results show that the residual strain of coal samples increases rapidly with the increase of vibration times at the beginning of dynamic load loading stage, and then gradually tends to be gentle. The permeability of coal samples increases exponentially with the increase of dynamic load frequency and CSR, while it changes in a negative exponential function with the initial adsorption gas pressure, and CSR has the most significant effect on the mechanics and permeability of coal samples. The peak strength and elastic modulus of gas-bearing coal samples after damage are negatively correlated with dynamic load frequency, CSR and gas adsorption pressure. When CSR is 0.75, peak strength and elastic modulus degradation rate reach the maximum, which are 15.3% and 68.2% respectively, and the damage variable is 0.68. Using CT scanning and three-dimensional reconstruction technology, the quantitative characterization of pore volume changes before and after loading of coal samples was obtained. The total pore volume increased to 7 times of the initial state under different CSR loading. The influence characteristics of dynamic load on the porosity of coal samples were analyzed, and the effects of mine vibration stress on the development of pore cracks, seepage characteristics and damage deformation of coal were explained. The research can provide support for the mechanism revelation and disaster warning of deep coal-rock gas dynamic disasters under the action of mine earthquake.