Research on effect of gas pressure in the development process of gassy coal extrusion

•Effect of gas pressure on development process of gassy coal extrusion is conducted.•Little gas expansion energy is released at low rate during the process of extrusion.•Gas pressure mainly contributes to promoting the destruction and extrusion of coal.•Gassy coal extrusion transforms into outburst at gas pressure beyond the limitation. Coal mining safety is always the most important issue in China due to a number of incidents. Gas outburst in coal mining is still occupied the main proportion of major incidents, among which gassy coal extrusion, as one type of gas outburst, presents an increasing frequency and threatens miners’ lives and property safety. As one of the main influencing factors, gas pressure has a significant effect on the development process of gassy coal extrusion. In order to investigate the effect of gas pressure on gassy coal extrusion, a group of experiments under different gassy pressures was conducted, based on which the extrusion intensity, coal failure mode and variation laws of gas pressure were observed, and gas expansion energy was calculated. The results show that during the process of gassy coal extrusion, very little gas expansion energy is released at a low rate; besides, gas mainly contributes to promoting the destruction and extrusion of coal. The increment of gas pressure promotes development of gassy coal extrusion and transforming of gas incidents. The relative intensity increases from 2.88% to 5% due to the gas pressure increasing from 0.3 MPa to 0.5 MPa. Gassy coal extrusion transforms into gas outburst when gas pressure is beyond the limitation, corresponding relative intensity turning to 43.31%. Gas is released in an obvious sequence in the process of gassy coal extrusion.