Simulation test study on coal and gas outburst under conditions of high in-situ stress

The occurrence mechanism of deep coal and gas outburst must be significantly different from the shallow part. Taking 12 coal seam in a Liaoning mine as the research background, using the self-developed simulation device for the whole process of coal and gas outburst that can apply axial pressure, confining pressure and pore pressure at the same time, the axial pressure simulates the stress effect of the overlying rock, the confining pressure simulates the surrounding rock stress, and the pore pressure simulates the gas pressure. Simulation tests of coal and gas outburst under high in-situ stress conditions with buried depths of 1 100, 1 300, 1 500, 1 700, 1 900, 2 100, 2 300 and 2 500 m were carried out and their reliability was verified. The relationship between relative prominent strength, critical gas pressure and buried depth is obtained. The results show that: ① The characteristics of coal and gas outbursts in deep parts are obviously different from those in shallow parts, and the distribution of prominent coal powder is trumpet-shaped, mainly concentrated in the range of 15 m-25 m, and the mass proportion of outburst coal powder reaches 52%-63%; ② The relative outburst strength and critical gas pressure change trend of deep coal and gas have two stages. There is a boundary depth of 1 700 m, a violent change stage at a buried depth of 1 100 m-1 700 m, and a slow change stage at a buried depth of 1 700-2 500 m; ③ The instantaneous gas pressure of the deep coal and gas outburst has a “step effect”. The duration of the step effect decreases with the increase of the buried depth, and the step effect disappears when the the buried depth is 2 500 m, indicating that the coal and gas outburst have a greater outburst risk at this time.