Study on the law of stress distribution in the presence of remaining coal pillar in a close-distance coal seam and the reasonable location of the roadway

In order to reveal the impact of remaining coal pillar on roadway layout of the lower seam after the upper part of the close coal seam is reversely mined, theoretical analysis and numerical simulation are conducted in this paper. With the roadway to be excavated in a mine located in Shanxi as the research object, theoretical analysis and numerical simulation are performed to explore the evolution of stress field in the lower coal seam under the influence of the leftover coal pillar. Also, an analysis is conducted on the mechanism of deformation and destruction occurring to the roadway in the lower coal seam, so as to determine the rational layout of roadway in the lower coal seam and the optimal parameters related to roadway support. The research results are as follows. (1) The mining operations conducted in the upper coal seam affect the magnitude of the principal stress, the principal stress ratio and the principal stress deflection angle of the lower coal seam, causing different patterns of deflective stress in the lower coal seam. (2) With the center line of coal pillar as the axis of symmetry, the influencing factors for the lower coal seam are symmetrically distributed. The larger the distance from the centerline, the larger the deflected plastic zone of the roadway surrounding rock. (3) In order to determine the rational layout of the roadway, the study area is divided into two zones by considering the main influencing factors. Allowing for the mode of mining and to ensure safety, it is recommended that the roadway should be positioned at the edge of the H-II area, such as at the location that is 15-20 m or 40-45 m away from the study area. Taking into account these influencing factors, the original tunnel support parameters are optimized. According to the data collected through on-site mining pressure observation, the support optimization scheme achieves satisfactory results.