Abstract
The aim of this study is to obtain movement laws of overlying strata above a fully mechanized coal mining face backfilled with gangue and solve the problem of surface subsidence during coal mining. This study was carried out based on gangue backfilling mining of Jiulishan Coal Mine (Jiaozuo City, Henan Province, China) from the perspectives of deformation of backfilled gangue under compaction, surrounding rock of a stope, and activities of key strata. The method combining with rock mechanics, viscoelastic mechanics, control theory of rock mass under mining, and numerical simulation was used based on physical and mechanical characteristics of backfilled gangue. On this basis, the research analyzed the temporal-spatial relationships of activities of surrounding rock of the stope, compressive deformation of backfilling body, failure depth of the floor, deformation characteristics of the main roof with laws of surface subsidence. The movement characteristics of overlying strata above the fully mechanized coal mining face backfilled with gangue and the traditional fully mechanized mining face were compared. It is found that, under the same conditions of overlying strata, movement laws of overlying strata are mainly determined by the mining height of coal seams and the heights of a caving zone and a fracture zone are nearly linearly correlated with the mining height. Through analysis based on thin-plate theory and key stratum theory, the location of the main roof of the fully mechanized coal mining face backfilled with gangue in coal seams first bending and sinking due to load of overlying strata was ascertained. Then, it was determined that there are two key strata and the main roof belongs to the inferior key stratum. By using the established mechanical model for the main roof of the fully mechanized coal mining face backfilled with gangue and the calculation formula for the maximum deflection of the main roof, this research presented the conditions for breaking of the main roof. In addition, based on the theoretical analysis, it is concluded that the main roof of the fully mechanized coal mining face backfilled with gangue does not break, but bends. The numerical simulation results demonstrate that, with the continuous increase of strength of backfilled gangue, the stress concentration degree of surrounding rock reduces constantly, so does its decrease amplitude. Moreover, the compressive deformation of backfilling, failure depth of the floor, and bending and subsidence of the main roof continuously decrease and tend to be stable. The mechanical properties of backfilling materials determine effects of gangue backfilling in controlling surface subsidence. Gangue backfilling can effectively control movement of overlying strata and surface subsidence tends to be stable with the increase of elastic modulus of gangue.
Highlights
Coalbed methane development, groundwater exploitation, and mineral exploitation are main factors leading to surface subsidence; surface subsidence is more obvious in the case of full-seam mining or mining with a large mining height (Figure 1). e main influences of coal seam mining on the surface are characterized by surface subsidence and large cracks on the surface. is leads to surface subsidence, landslide, and damage to farmland, houses, and roads
According to the deformation law under compaction of waste fillings and cracked immediate roof, they deduced the relational expression of mechanics of support strength in the backfilled fully mechanized coal mining face. e study proves the feasibility of gangue backfilling mining and concludes the law of strata behaviors in fully mechanized coal mining face backfilled with gangue through field application
Numerical simulation results demonstrate that floor strata mainly undergo nearly horizontal displacement, while roof strata mainly experience vertical subsidence, either with or without backfilling. e integrity of roof strata is improved as the extent of backfilling increases and the range of displacement increases. e conclusions are proved by results from a field experiment. e similar simulation and field measurement are performed on movement laws of overlying strata above the working face backfilled with gangue, which provides a reliable theoretical basis for backfilling mining [21, 22]
Summary
Groundwater exploitation, and mineral exploitation are main factors leading to surface subsidence; surface subsidence is more obvious in the case of full-seam mining or mining with a large mining height (Figure 1). e main influences of coal seam mining on the surface are characterized by surface subsidence and large cracks on the surface. is leads to surface subsidence, landslide, and damage to farmland, houses, and roads. E study proves the feasibility of gangue backfilling mining and concludes the law of strata behaviors in fully mechanized coal mining face backfilled with gangue through field application. In the based on the characteristics of strata movement of solid backfilling mining technology, Guo et al [47] proposed the surface subsidence prediction method based on the equivalent mining height theory and described the parameter selection guideline of this method. By conducting a field experiment in a Chinese coal mine located under thick unconsolidated layers, Wang et al [48] proposed a backfilling strip mining method via determination of the appropriate longwall face length and mining height, to protect the bearing structure from being damaged, avoiding surface collapse. This study analyzed gangue with different elastic moduli, clarified influences of mechanical parameters of gangue on surface subsidence, and determined reasonable physical and mechanical parameters of gangue
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