Evaluating the Safety of Using the Combined Mining Method in Close-Distance Coal Seams

This study aimed to investigate the internal dislocation law of coal seam working face under coal pillars with different widths and evaluate the safety of using the combined mining of close-distance coal seams under different layer spacing. Based on elastic–plastic mechanics and mine pressure theory, theoretical calculation and numerical simulation were implemented to establish a numerical model consistent with the actual production. Based on the theoretical and simulation results, the abutment stress distribution of surrounding rock in coal seam stope was analyzed and the stress transfer law of coal pillar floor under the influence of different coal pillar width and floor depth was studied. Finally, this paper analyzed the limit span of goaf under two different beam structures. The results indicate that with the same coal seam distance, the interior dislocation distance increases linearly with the increase of coal pillar width. With the increase of floor depth, the vertical stress under the coal pillar decreases, but the influence area increases slightly. Finally, the ultimate spans of two different beam structures were calculated. In summary, this paper explored the strata behavior, i.e., the deformation and failure mechanism of surrounding rock in coal seam mining. The research results demonstrated the feasibility of using the combined mining method in close-distance coal seams. The methodology proposed in this paper could be implied in similar working environments, and this study provides new insights into the mining technology in lower coal seams.