Mining subsidence analysis of gently inclined coal seams based on FLAC^3D and DEM data

Shizuishan Mining Area in Ningxia Province is located in the western Yellow River. The subsidence of the mined-out area causes frequent surface ecological and environmental problems. The analysis of coal mining subsidence will play a positive role in environmental remediation the Yellow River Basin. Taking Shizuishan Coal Mine as an object to study the evolution characteristics of surrounding rock stress and displacement field of gently inclined coal seam, a three-dimensional numerical model of the gently inclined coal seam based on the numerical simulation software FLAC^3D was established. The variation of stress, plastic zone, and displacement in the surrounding rocks in goaf were calculated and analyzed, and the surface displacement variation of the coal mining area was obtained from the bi-temporal images DEM superposition statistics which was verified with the numerical simulation results. The results showed that mining activities destroyed the stress balance of the surrounding rocks and causes stress redistribution. An obvious stress concentration appeared in the roof and coal pillar of the goaf. The maximum principal stress decreased gradually from coal seam roof to surface. The vertical displacements of the rock formation near the mining area were larger, and gradually decreased as it moved away from the mining area. After the end of three level coal seam mining, the maximum vertical displacement of the surface was about 12 m. With the increasing area of the mined-out area, the plastic zone around the mined-out area and corners gradually extended and expanded, which was mainly shear failure. The surface subsidence basin was asymmetric. The two subsidence centers occurred in the middle of the subsidence basin and downhill direction, and the influence range on downhill direction was larger than uphill direction. The settlement results and trends were basically consistent with both the numerical method and two-phase DEM overlay statistical analysis. The research results can provide a reference for safe mining activities and a new method for ground subsidence monitoring.