Stress distribution characteristics of overburden strata during thick coal seam top coal caving

Given the lack of systematic research on the movement of overburden strata and damage characteristics of floor residual coal in the process of thick coal seam top coal caving, this study takes the Anping Coal Mine as the engineering background. The spatiotemporal evolution of overburden collapse, force chain transmission, and floor stress redistribution was investigated via the FLAC^3D‒PFC coupled numerical method. Owing to the large mining space of the thick coal seam, the collapse of the roof has the progressive characteristic of "first two ends, then the middle", with a measured collapse angle of approximately 57°, forming an evident caving band and residual coal accumulation zones. Moreover, the force chain network in the goaf evolves from sparse to dense, gradually forming a stable load-bearing structure. In addition, the porosity of the floor fluctuates from a wide range (0.15-0.43) to a more stabilized level (0.18-0.40) after compaction. Correspondingly, the vertical stress in the center of the residual coal floor increases from nearly 0 MPa to 1-3 MPa as the overburden load is transferred downward. The research results have important reference value for the destabilization mechanism of surrounding rock in thick coal seam mined-out areas and the design of residual coal remining and provide feasible ideas for improving mine productivity and guaranteeing safe production and the sustainable development of coal resources.