Collaborative gas drainage technology of high and low level roadways in highly-gassy coal seam mining

China's coal resources are gradually being mined deeper. The gas content and emissions of deep coal seams increase significantly compared to shallow seams. In the mining of the highly-gassy coal seams, strengthening gas drainage in the goaf and fissure zone can improve the efficiency of coal seams and reduce carbon emissions. However, the method of the borehole or high level roadway often cannot meet the demand of goaf and fracture zone gas drainage. Thus, a new technology of gas drainage in goaf and fracture zone is proposed: cooperative gas drainage via high and low level roadways. Taking the Pingshu coal mine as an example, the gas flow field model of the goaf was established. Fluent software was used to analyze and simulate different gas drainage effects of high and low level roadways under different layers and negative pressure conditions, and to optimize the process parameters of high and low level roadways. The results show that the collaborative drainage effect of high and low level roadways is much better when the horizontal and vertical distances of high level roadway are 32 m and 30 m, the horizontal distance of low level roadway is 5 m, and the negative drainage pressure of both roadways is 15 kPa. The gas concentration in the upper corner can be effectively reduced under the condition. On the basis of the optimized parameters, the collaborative gas drainage of high and low level roadways was applied and effectively solved the problems of gas accumulation and overrun in the upper corner of the working face, where the gas concentration was less than 0.45%. The paper provides a new approach for gas drainage in the highly-gassy coal seams.