Deterioration of compressive properties of coal rocks under water and gas coupling

The compressive properties of coal under water-gas coupling were studied based on the water-rock-gas coupling test system. The compressive strength and deformation damage characteristics of the coal samples were analyzed, and the macro and fine degradation mechanisms of coal under water-gas coupling were revealed. The compressive strength of the coal samples under the three soaking conditions was reduced compared to that of the dry coal samples. The damage mode of coal samples changed from tensile damage of dry coal samples to mixed shear-tensile damage. Coal samples changed from brittle damage to plastic damage, which increased the range of localization zones and the misalignment of coal samples after soaking. The deterioration effects of coal samples in the three soaking environments were mainly as follows: 1) The intrusion of water and gas led to the decomposition and precipitation of clay minerals inside coal samples; 2) The surface of each group of coal samples showed a deterioration effect after soaking; 3) The deterioration effect of water and gas changed the internal pore structure of coal samples. The destruction of the original supporting structure of the coal samples in the soaked environment reduced the ability of the coal samples to store energy before destruction.