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This paper presents a comprehensive analysis of roof strata conditions, shield pressure, and ground surface subsidence above Panel 42105 of the Buertai Coal Mine in Inner Mongolia, China. A 3D geological model and a 2D numerical simulation model are established to examine the roof strata structures with varying strata conditions. Numerical simulation results demonstrate that the hard rock 1 and 2 roof layers are, on average, likely to break 20 m and 57 m behind the coal face, respectively. It is concluded that when the immediate roof is relatively thin, a cantilever beam is formed, whereas a Voussoir beam is formed when the immediate roof is relatively thick. The patterns of shield pressure and surface subsidence under different roof conditions are also examined. The shield working pressure under the Voussoir beam structure appears to be lower than that under the cantilever beam structure. The average horizontal distance behind the working coal face at which the maximum surface subsidence occurs is 92.1 m. On-site monitoring data are used to explain the causes of the unusual shield pressure and its relation to surface subsidence. Finally, guidelines to predict the shield pressure under similar conditions are provided. [ABSTRACT FROM AUTHOR]

To better understand water inrushes originating from shaft-freezing holes, the hydrogeological conditions and water source were analyzed for a typical inrush case in the Yingpanhao coal mine in western China. The mechanism of this new type of water inrush was identified by considering the stratum movement caused by mining, the concentric annular channels of freezing holes, and the dynamic recharge of multiple aquifers. A new risk assessment model and corresponding grouting method were developed and the problems involving the prediction of water inrush and selection of the optimum grouting position were described. Detailed guidelines for grouting, including the layout of injection boreholes, slurries, grouting pressure and stopping criteria, were proposed. A grouting case targeting this type of water inrush in the Yingpanhao coal mine was introduced. Field studies indicated that open, concentric annular freezing hole channels provide favorable conditions for groundwater migration. The proposed method may effectively inhibit groundwater migration in multiple aquifers and prevent water inrushes through shaft freezing holes and provides an appropriate framework for water inrush prevention for similar mining areas in western China. [ABSTRACT FROM AUTHOR]

Aiming at the problem of mining coal resources under the Yuxing Mine Ecological Park in Inner Mongolia, China, we adopted a continuous mining and continuous backfilling (CMCB) cemented-fill mining method; based on the systematic description of the mining and backfilling craft of the CMCB mining process, comprehensive use of theoretical analysis, numerical simulation, and similar simulation test methods to analyze the control mechanism of overlying strata. By establishing the mechanical model of roof movement for the CMCB mining, the roof deflection curve equation is deduced, and the roof instability criterion is put forward based on the maximum tensile stress criterion. Numerical simulation showed that the stress curve at the shallow part of the roof fluctuates up and down in a "w" shape, the stress curve of the upper surrounding rock sinks slowly, and the coal pillars and filling bodies are alternately loaded during the staged mining process to jointly limit the movement of the overlying strata. The similar simulation test results showed that the roof has no structural damage, the roof cracks are not obvious, and the overlying strata control effect is good. On site tests showed that the CMCB mining method can effectively limit the movement of the overlying rock in the stope, control the surface subsidence of the ecological park, and increase the recovery rate of coal resources. It can provide a reference for the development of coal resources and ecological protection in a fragile environment. [ABSTRACT FROM AUTHOR]