Influence of coal seam gas pressure on the propagation mechanism of outburst two-phase flow in visual roadway

•A coal and gas outburst visual simulation system was developed and outburst experiments were conducted.•The propagation and characteristics of the outburst two-phase flow in the roadway were studied.•The evolution of shock wave overpressure was analyzed and the velocity of wave front was calculated. Coal and gas outbursts are serious disasters that occur during coal mine production. In these instances, the outburst two-phase flow is the main cause of casualties. To investigate the propagation and mechanism responsible for the disaster of the outburst two-phase flow, a visual test system for coal and gas outburst simulation was independently developed. The outburst simulation experiments under different gas pressures were carried out and the propagation process of outburst two-phase flow in a visual roadway was monitored in real time to analyze the propagation mechanism and outburst intensity. The experimental results showed that the first shock wave overpressure reached its peak value immediately after the outburst and the characteristics of turbulent pulse appeared at the front of the outburst cavern, which was followed by one to two successive waves with lower peak values in the negative-pressure region. The flow pattern of pulverized coal observed in the visual roadway included suspended, stratified, dune, and plug flows. The velocity of pulverized coal flow was calculated based on the image method, which can be divided into the acceleration phase, and the acceleration and deceleration cycling phases. When the gas pressure increased from 0.35 MPa to 2.0 MPa, the velocity of pulverized coal flow increased from 34.19 m/s to 71.20 m/s, while they had a nonlinear relationship. The shock wave propagated in the roadway ahead of the pulverized coal flow at supersonic speed, and the velocity of shock wave front was as high as 344.75–370.02 m/s, which was much higher than that of pulverized coal flow. The higher the gas pressure was, the more pulverized coal ejected, and the relative outburst strengths increased from 36.1% to 63.7% with the increase of gas pressure from 0.35 MPa to 2.0 MPa.