Control effect of coal mining solid-waste backfill for ground surface movement in slice mining: a case study of the Nantun Coal Mine

Management of solid waste and protecting the ecological balance of the region are key challenges that the coal mining industry has to face. This study evaluated the effect of solid waste backfilling mining on the overlying strata movement and surface deformation variation pattern in slice mining. The mechanical characteristics of different cemented paste backfills (CPB) were compared. The CPB specimens were made of coal gangue and cement with or without the addition of fly ash. The experiments showed that the mechanical strength of the CPBs made of coal gangue and cement increased dramatically. A numerical simulation was then performed to analyze the variation patterns of the overlying strata displacement and surrounding rock stress distribution before and after filling the 3(lower) and 3(upper) coal seams with CPB. The CPBs reduced the movement of the surface by 95.1% and 95% during the mining of the 3(lower) and 3(upper) coal seams, respectively. Finally, we used a mining-induced subsidence prediction and analysis system to predict the influence of the 3(lower) and 3(upper) coal seams on the ground surface subsidence. It was found that the ground surface subsidence induced by CPB mining was 1/20 that of the cumulative ground surface subsidence caused by caving mining. CPB mining could effectively control the ground surface subsidence caused by multi-slice mining of the thick coal seam, offering protection for buildings above the ground. Our research provides theoretical and technical support for coal mining under buildings subjected to similar conditions.