Hydrogeological characteristics and danger-solving mining of Jurassic Baotashan sandstone—A case study in New Shanghai No.1 coal mine

The western mining area is an important energy strategic base in China. The Jurassic coalfields have many mineable coal seams and rich resources. The middle and lower coal seams are seriously threatened by the "Baotashan sandstone" aquifer. However, the research on this aquifer is few and the data is scarce in China. Taking the "11·25" water inrush hazard of New Shanghai No.1 coal mine as an example, the extended drainage drilling, supplementary hydrogeological exploration and underground water drainage test were carried out. It was found that the aquifer was characterized by complex sedimentary structure, uneven water-rich, abundant static reserves, high water head, large water pressure and easy drainage. SEM showed that the sandstone is of argillaceous cementation, massive structure, and endogenous pore development. Taking the total thickness of sandstone, the ratio of sand to land, the unit water inflow and the permeability coefficient as the main controlling factors, the law of water-rich property of the aquifer was analyzed. It was estimated that under normal conditions, the water inflow is 1 200.7 m³/h and the maximum water inflow is 1 860.8 m³/h, which excess the capacity of mine drainage. Based on the analysis of the boundary conditions of hydrogeological units, a three-dimensional numerical model of unsteady seepage field was established by Visual MODFLOW, and the crisis-solving effects of four drainage stages were simulated, the danger of water inrush from 18 coal seam in one district could be relieved.