# Pressure-Relief Gas Cooperative Drainage Technology in a Short-Distance Coal Seam Group
## 1 Introduction  
China's gas disasters are extremely severe [1]. Ninety-five percent of high-gas mines are in low-permeability coal seams, and the adsorbed gas content accounts for more than 80% [2, 3]. In a high-gas coal seam group, protective layer mining, combined with pressure-relief gas extraction, is the most economical and effective measure for gas disaster prevention and control [4, 5, 6]. However, with coal seam spacing of less than 10 m, no matter which layer is selected as the first mining protective layer, the adjacent layers are all in the pressure-relief range [7, 8]. The gas in the pressure-relief state has the characteristics of a large desorption amount and a fast desorption speed [9]. Under the combined action of gas pressure and the negative pressure of ventilation, the pressure-relieved gas flows through overburden fractures to the mining layer [10]. At present, pressure-relief gas extraction is an effective technical measure to control gas in short-distance coal seam groups. Scholars have undertaken considerable research into the pressure-relief gas treatment technology of short-distance coal seam groups. [PERSON] [11] studied the evolution law and distribution characteristics of overburden fractures for repeated mining in short-distance seam groups. Using numerical simulation, [PERSON] [12] studied stress evolution and nonlinear action after multiple depressurization mining in short-distance seam groups. [PERSON] [13] analyzed the gas permeation evolution mechanism of coal seam mining and proposed a comprehensive extraction technology. [PERSON] [14] studied the treatment technology of stress release gas in short-distance seam groups using physical experiments. [PERSON] [15] and [PERSON] [16]proposed the technology of pressure-relief gas extraction using large diameter boreholes. [PERSON] [17] and [PERSON] [18] studied the permeability-increasing effect of high-level drainage roadways in the process of coal seam group mining. [PERSON] [19] and [PERSON] [20] investigated the effect of pressure-relief gas drainage from adjacent seams using high-level boreholes and field tests. [PERSON] [21] developed RCPNMs to calculate the topology and geometry properties of explosively created fractures. In summary, predecessors have adopted high drainage roadways, roof (floor) plate drilling, roof high (low) drillings, and goat buried-pipe extraction methods for gas control, depending on the coal seam occurrence conditions and technical processes. Their research results have provided theoretical and technical support for gas prevention and control of short-distance coal seam groups. However, many problems have not yet been fully resolved. Although the extraction volume of a high drainage roadway is large, it also requires much engineering work and is expensive. Furthermore, the perforation speed of the top (bottom) plate is rapid, but it is difficult to maintain the drilling. Moreover, although the layout of the buried-pipe extraction is flexible, and the investment costs are low, the position of the buried-pipe orifice can be affected, resulting in the disadvantage of a poor extraction effect. The existing research on gas control in short-distance coal seam groups has focused on the determination of single technical parameters. The layout parameters of pressure-relief gas extraction holes in adjacent strata mostly depend on field measurements or empirical formula estimation of the height of the \"three-vertical zones\" of traditional strata movement. When the influence of the difference in overburden structures of short-distance coal seam groups on gas migration and the enrichment of the adjacent seams is ignored, it becomes clear that the research into gas control measures and the determination of specific parameters is not sufficiently comprehensive. In this paper, the 1211 working face of Shanxi Jinhui Wanfeng Coal Mine was taken as the research object.