A novel assessment method for upward mining feasibility in close-multiple coal seams and its application

Upward mining is a mining method for the upper residual coal resources in close-multiple coal seams. However, as the first step of the upper residual coal seam with upward mining, the assessment of the upward mining feasibility plays a significant role in the safe and efficient extraction of the upper coal seam. Based on the theory of damage height of interlayer strata, a novel assessment method for upward mining feasibility is proposed, which is named the SHR (subsidence-height ratio of the upper coal seam) method. Through comprehensive research methods of theoretical analysis, numerical simulation, physical modeling, and on-site detection, the accuracy of upward mining feasibility by the novel method is verified. The main research results show that: (1) The damage height of interlayer strata (DHILS) is positively correlated with the buried depth of the lower coal seam. (2) The SHR method effectively realizes the assessment of the upward mining feasibility of the upper coal seam. The upward mining is unfeasible when the SHR (η) is less than 0. Conversely, the upward mining is feasible. (3) The critical subsidence-height ratio of the upper coal seam (ηc) is also given, which helps analyze the difficulty degree of upward mining. (4) The accuracy of upward mining feasibility by the SHR method is verified, compared with the traditional methods. (5) The SHR method is employed to predicte the upward mining feasibility of the No. 9 coal seam within the whole area of Fangezhuang Coal Mine. The predicted result of the SHR method is consistent with the actual mining situation effectively identifying infeasible mining areas, feasible mining areas, and difficult mining areas. This study enriches the assessment methods for upward mining feasibility, especially for the residual upper coal seam with deep buried depth.