Numerical analysis of coal rock gas dynamics disaster risk in coal thickness variation area and research on prevention and control.

During the mining process of deep coal mines, the coal thickness variation zone is highly prone to coal-rock-gas dynamic disasters. In order to promote the sustainable development of coal resource exploitation and utilization, the numerical simulation was carried out based on COMSOL software. The dynamic disaster mechanism of coal rock gas in the coal thickness variation area was revealed and corresponding prevention and control measures were given. Research shows that the stress concentration degree in the coal thickness variation area is higher. Compared with the non-variation area, the peak stress concentration coefficient increases by 29.4%, with the maximum value being 2.29. There is a temporary increase zone of gas pressure in front of the working face, with the maximum gas pressure reaching 0.82 MPa. The plastic zone in the coal thickness variation area is unevenly distributed, and the plastic deformation of the coal body in the thick coal zone is relatively large. The coal thickness variation zone and the thick coal zone accumulate a large amount of gas expansion energy. The gas expansion energy contained in the unit volume of coal obtained from the simulation is more than six times the elastic energy of the unit volume of coal and rock mass. The gas expansion energy plays a dominant role in disasters. When the coal seam is excavated from thin to thick in the coal thickness variation zone and thick coal zone, the peak energy criterion in the area near the working face is greater than 1 and keeps increasing, indicating that dynamic disasters occur and the degree of harm gradually increases. Comprehensive analysis shows that excavation from thick to thin is more likely to induce rock burst than excavation from thin to thick. Excavation from thin to thick is more likely to cause coal and gas outbursts than excavation from thick to thin. Practice shows that when using the high-pressure water jet slit drilling technology to prevent and control dynamic disasters in the coal thickness variation area, the reasonable slit spacing of coal seam drilling should be set at 3 m, and the average pure amount of gas extracted per hole is 2.6 times that of the ordinary drilling without slits. The hole spacing for drilling in coal seams of equal thickness and coal thickness variation areas should be set at 6 m and 8 m respectively. The stress peak is transferred to the deep part, which can effectively reduce the gas expansion energy and weaken the concentrated stress of the coal seam, and at the same time achieve the purpose of preventing outburst and eliminating protrusions.