Numerical simulation and discharge evaluation of Cenozoic “bottom aquifer” under drainage conditions

The coal seam mining in the east of China will cause the groundwater of the bottom aquifer of the Cenozoic (referred to as “bottom aquifer”) to indirectly recharge the sandstone aquifer under the bedrock surface, which will not only lead to ground settlement, but also increase the mine drainage. The drainage amount is indeed a certain basis for the prevention and control of mine water damage and the prediction of settlement amount. Taking Banji Mine in Huainan Coalfield as an example, a numerical model of “bottom aquifer” was constructed by analyzing the relationship between the sandstone aquifer of 9^# coal roof and the overlying “bottom aquifer” recharge, its hydrogeological parameters were obtained, and its output was calculated and evaluated by water balance principle. The results show that the “bottom aquifer” in the study area can be divided into 5 hydrogeological unit blocks, the permeability coefficient is 0.433-0.824 m/d, the elastic water release rate is 1.8×10⁻⁶-3.6×10⁻⁶ m⁻¹. Under the condition of sandstone water drainage, the “bottom aquifer” discharge at different stages accounts for about 1/4 of the total drainage water, and its sources are mainly lateral recharge and static reserve consumption. Therefore, through the grouting of weathering zone of bedrock, the hydraulic channel between the bottom and the roof of coal seam is an effective measure to control the recharge of sandstone water from the bottom water.