Experimental investigation on the mechanical characteristics of gas-bearing coal considering the impact of moisture

Water is an inherent component in coal masses. The presence of moisture has a significant impact on the mechanical properties of gas-bearing coal and plays a key role in the development of coal and gas outburst disaster. However, how moisture affects the mechanical behavior of gas-bearing coal is poorly understood. In this research, a series of triaxial compression and acoustic emission (AE) tests were performed on gas-bearing coal under different water treatment conditions. The results show that moisture reduces the change in surface energy of the coal by methane adsorption due to the predominance of water adsorption. Therefore, the influence of moisture is more prominent than that of methane and results in a reduction in strength and enhancement in the gas softening coefficient with increasing moisture content. Simultaneously, AE activity of gas-bearing coal is significantly inhibited by moisture, and two failure types can be determined based on the AE results around peak stress: a sudden rupture type for dry and low-water-bearing coal and a stable rupture type for water-saturated coal. Moreover, a meso-statistical damage model is proposed, which agrees well with the experimental results. An analysis indicates that the moisture in coal can reduce the surface energy and weaken the bonds among coal matrix particles, which not only changes the strength of gas-bearing coal but also restrains the energy release during failure; thus, moisture promotes the development of damage in gas-bearing coal.