Analysis of the Influence of Boundary Permeability Characteristics Under Fluid-Solid Coupling on Surface Subsidence in Deep Near-Horizontal Coal Seam Mining

The fluid-solid coupling effect is an important factor which cannot be ignored to study the surface subsidence of deep coal seam mining in the area with abundant underground water. To study the influence of boundary permeability characteristics on surface subsidence in deep near-horizontal coal seam mining under the effect of fluid-solid coupling, the pore water pressure field, vertical stress field, surface subsidence, and vertical displacement of a rock seam during deep mining under different permeability boundary conditions were analyzed based on fluid-solid coupling theory, taking the 3-1501 working face of Erdos Hongqinghe coal mine as an example. The results revealed that the permeability characteristics of different hydraulic boundaries affected the pore water pressure, vertical stress in the rock layer, and surface subsidence during deep mining. Moreover, the trends of pore water pressure, vertical stress, and surface subsidence of a fixed-head permeability boundary were largely the same as those under impermeable boundary conditions, but the calculated results of the fixed-head permeability boundary were lower than those for the impermeable boundary at the same depth. The maximum surface subsidence for the fixed-head permeable boundary condition and the impermeable boundary condition was 879 and 925 mm, respectively, which were 239 and 285 mm higher than those obtained when the fluid-solid coupling effect was neglected (an increase of 37.3% and 44.5%, respectively). The field monitoring trend for the subsidence basin aligns closely with the subsidence basin trend under the influence of fluid-solid coupling. Considering the constant head permeable boundary conditions in the context of fluid-solid coupling yields accurate surface subsidence results. The results have provided a theoretical basis for the analysis and prediction of coal mining surface subsidence considering the fluid-solid coupling effect.