Water level evolution pattern of loose layers under water cutoff curtain in ecologically fragile open-pit mines

Eastern Inner Mongolia of China is characterized by a fragile ecological environment and scarce water resources. High-intensity mining in open-pit coal mines has caused drastic changes in the recharge, runoff and discharge of the groundwater system, resulting in a significant drop in the water level of the loose layer, depletion of surface stream flow and destruction of the ecological environment. To reveal the evolution of water level in the loose layer under the water cutoff curtain in ecologically fragile open-pit mines, analyze the characteristics of groundwater distribution in and the influence of mining on the water level of loose layers, we carried out, theoretical calculations and physical simulations of the water level in the loose layer under the water cutoff curtain. Then, the evolution of the water level in the loose layer in Zhanihe open-pit coal mine and Yuanbaoshan open-pit coal mine were analyzed. The results show that the loose layer in the ecologically fragile open-pit mine area has a large permeability coefficient and shallow water level burial. Open-pit mining has a huge impact on the water level of the loose layer in the mine area, and the water level of the loose layer within several kilometers around the mine area decreases by several meters to tens of meters. In addition, theoretical calculations and physical simulations show that the water level of the loose layer outside the cutoff curtain gradually rises with the increase of the curtain length, and the water level changes at a relatively stable rate, while the water level changes relatively drastically near the curtain. The monitoring results of Zhanihe open-pit coal mine and Yuanbaoshan open-pit coal mine show that the water level of the loose layer outside the curtain rises by 3.43-9.12 m, and the water level of the loose layer inside the curtain decreases by 3.21-10.15 m. The increase of the water level of the loose layer outside the curtain is proportional to the completion rate of the water cutoff curtain. The theoretical calculation and physical simulation results of the water level in the loose layer under the water cutoff curtain can provide guidance for the field engineering application, and the water cutoff curtain can significantly raise the water level in the loose layer around the ecologically fragile open-pit area, protecting the water resources in the loose layer.