Collaborative Gas Drainage Technology of High and Low Level Roadways in Highly-Gassy Coal Seam Mining

China's coal resources are being mined gradually deeper. Compared with the shallow part, the content and the emission of gas are significantly increased in the deep coal seam. In the mining of the highly-gassy coal seam, strengthening gas drainage in the goaf and fissure zone can improve the efficiency of the coal seam 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 model of gas flow field in the goaf was established. Different gas drainage effects were analyzed and simulated by using the Fluent software with the different layers and negative pressures of high and low level roadways and the technological parameters of the high and low level roadways were optimized. 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 at the condition. Based on 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