Water inrush mechanism and prevention for thick coal mining under an extremely thick glutenite layer: a case study in the southwest of the Ordos Basin

The hydrogeological conditions in the Ordos Basin differ greatly between east and west, so also do the water inrush patterns and prevention methods during mining. Taking the example of the Huating mining area in the southwest of the Ordos Basin, the physical and mechanical characteristics of the overburden under the glutenite aquifer are analyzed through rock-mechanics, X-ray diffraction, scanning electron microscopy, and acoustic-emission tests. From in situ observations and similarity simulation tests, the overburden failure characteristics and evolution law are researched. The research results show that the overburden strata under the glutenite aquifer contain medium-hard rock. The clay mineral content is relatively high in the mudstone, which have good water-resisting properties. The strength increases with confining pressure, and the sandstone is significantly stronger than the mudstone. The glutenite aquifer is weakly cemented, in which tensile–compressive deformation occurs during mining. Tensile deformation increases the pores and fractures, thereby giving rise to ample water storage space. The heights of the fractured and caved zones are 12.84–13.26 and 5.34–5.56 times the mining height, respectively. There are three zones where the thickness of the overburden strata under the glutenite aquifer is less than that of the waterproof rock pillar. The glutenite aquifer in the northern area I should be drained before mining to reduce water catchment during mining, while either height-limited mining or pre-mining water drainage can be used in areas II and III. Coal can be mined normally in the medium water-rich area and underneath the Black River.