Discussion on the water-preserved coal mining by dewatering-reflooding water curtain in open-pit coal mines

To suppress the attenuation of groundwater resources caused by drainage and control the influence range of coal mining on groundwater resources, the coal mining technology with water curtain was adopted. Taking an open-pit coal mine as the background, this paper established a sand trough recharge platform to carry out physical experiments, and used a numerical method to simulate the irrigation area, so as to analyze the formation and variation of the dewatering-reflooding water curtain. Physical experiments were carried out to observe the formation of a fixed head boundary by water injection curtain which prevented the expansion of funnel, the influence of different heights of water injection curtain head on water injection volume and the optimal water head which balanced the water injection and excretion were obtained. The numerical simulation results were similar to that of physical simulation. Under the condition that the aquifer falling funnel had been formed, the closer the water injection curtain is to discharge area, the greater the recharge amount to reach the predetermined head. And it took longer for water level to recover to a predetermined value under the condition of a given amount of water injection. In both physical and numerical simulation, changing the position of the water injection curtain or the height of the water head can make the pit drainage equal to the water injection of the curtain, which can minimized the external displacement of drainage water. The experiment and numerical simulation show that the water injection curtain is expected to be a practical model for water-preserved coal mining in open-pit coal mines in China.