Effect of Strata Conditions on Shield Pressure and Surface Subsidence at a Longwall Top Coal Caving Working Face

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.