Pressure relief and gas outburst prevention in ultra close coal seams a case study on overlying underlying interactions

Abstract

Abstract Ultra-close coal seams are adjacent coal seams in a mining area with a spacing of less than 5 m. They have strong interactions during mining. Due to the small distance between layers, mining the upper coal seam creates a pressure relief zone. The lower coal seam enters this zone, which helps release gas pressure and prevent outbursts. This process reduces gas drainage work, supports gob-side entry driving, improves mining efficiency, and promotes sustainable coal resource development. During upper coal seam mining, stress often concentrates in residual coal pillars. Mining-induced stress transfers through rock layers to nearby working faces, changing the stress distribution in the lower coal seam. Roof collapse in the goaf can cause instability, making stress changes more complex. This leads to strong strata pressure and increases mining risks. Determining the pressure relief range of the lower coal seam is key to optimizing gas control and ensuring safe mining. This study focuses on the W8 coal seam (W8-32030 panel) and its underlying W9-10 coal seam in Mine No. 6 of Pingmei Co., with the goal of determining the pressure relief and outburst elimination range. The study employed various methods, including numerical simulation, physical similarity simulation, and field monitoring, covering aspects such as plastic zone monitoring, stress and deformation coefficient monitoring, and gas monitoring. By combining the results from different methods, we obtained the pressure relief and outburst elimination range and performed a comparative analysis of the results from each method. The comprehensive analysis of the advantages of the results from different methods not only improved the accuracy of the study but also provided a reliable basis for a more thorough understanding of the pressure relief and outburst prevention effects in ultra-close coal seams. Finally, by integrating the results from all methods, we determined the pressure relief and outburst elimination range of the underlying coal seam to be 27.5 m. The findings of this study provide scientific guidance for practical mining operations, effectively supporting the rational layout of outburst prevention measures during coal mining and ensuring operational safety, thus holding significant engineering application value.