Experimental Study of Coal–Gas Outburst: Insights from Coal–Rock Structure, Gas Pressure and Adsorptivity

Coal–gas outburst is a complex dynamic phenomenon in underground coal mines that has occurred frequently over the past 150 years. This phenomenon has seriously restricted the efficient development of coal resources and it poses a great threat to global energy security. Physical simulation experiments under different conditions that considered the coal–rock combination structure and gas adsorptivity were carried out by using a true triaxial coal–gas outburst experimental system, and the experiments controlled for the type of adsorbable gas, the presence (or absence) of a roof and the gas pressure. The influence of the coal–rock structure and gas adsorptivity on the disaster occurrence conditions and dynamic response characteristics was discussed, and the gas–solid-coupling disaster-inducing mechanisms of coal–gas outburst under unloading were obtained. The results show that outburst pulverized coal does not present an obvious sorting performance under the experimental conditions of this work. All the outburst holes are characterized by small openings and large cavities. Coal walls around the holes are damaged by spallation, and the strength of the outburst holes is low, but relatively stable. Stronger gas adsorptivity and greater gas pressure correspond to more intense outburst dynamic effects. Moreover, greater outburst intensity corresponds to more obvious coal spallation characteristics. Whether there is roof or not has no significant effect on the sweeping and handling of thrown pulverized coal. Compared with the condition without roof, the existence of a roof will promote an increase in the outburst intensity and more obvious spallation damage of the outburst coal. The coal–gas outburst process includes four stages: outburst occurrence, rapid development, deceleration development and outburst termination. The research results have certain guiding significance for studies on the mechanism of coal–gas outburst.