凹陷式开采石灰岩矿区地下水渗流数值模拟

露天凹陷式开采石灰岩矿区的疏干降水过程将形成降水漏斗，并改变区域地下水流场；定量刻画开采条件下的地下水渗流对矿区涌水量预测及相关环境地质问题防治有重要的实际意义。以广东某石灰岩矿区为例，采用地下水渗流数值模型模拟了矿坑开采速度分别为4、5、8 m/a条件下的地下水流场变化过程。模拟结果表明：在开采条件下，研究区地下水位不断降低，水位下降速率与开采速度之间呈正相关关系；开采形成的降落漏斗将延伸至矿区所在水文地质单元边缘，形成时间与速度成反比；区域范围内的地下水位年内动态与降雨季节变化一致，波动幅度随与矿坑距离增加而减小、随渗透系数降低而增加，但受开采速度影响不明显。开采初期，矿坑涌水量随开采深度和开采速度增加而增大；但当矿坑开采深度达40 m时，研究区浅层第四系孔隙水和溶洞裂隙水基本疏干，涌水量基本不再随开采深度增加，以4、5、8 m/a速度开采的矿区稳定涌水量分别为7 970、8 240、9 030 m³/d。该研究结果可为类似石灰岩矿区开采方案设计及周边地下水位动态监测提供参考。

Numerical simulation study of groundwater seepage in the open-pit limestone mining area

The groundwater has to be drained inevitably at the open-pit limestone mining area, which would change the original groundwater flow field there. Therefore, describing the groundwater flow under mining condition quantitatively is practical to predict the mine discharge and prevent the environmental geological problems. In this paper, a numerical model is used to simulate the changes of groundwater flow in the limestone mining area in Guangdong province, with three mining speed that equal to 4m/a, 5m/a, and 8m/a respectively. The results show that the precipitation funnel with the mining speed of 4m/a, 5m/a, and 8m/a extends to the hydrogeological unit edge at the 10th, 10th and 5th years respectively, where the groundwater in the area discharges to the mine hole. The hydraulic head in the study area decreases with the increasing mining depth. And the decreasing rate of the head is correlated with mining speed positively. The annual dynamics of hydraulic head in the area is consistent with the seasonal variation of rainfall. The fluctuation range decreases with the growing distance from the mine and increases as the hydraulic permeability decreases. However, the mining speed affects the groundwater dynamics unconspicuously. At the early mining stage, the mine discharge enlarges with the increasing mining depth and mining speed. Once the mining depth reaches 40m, quaternary pore water and karstic fissure water in the study area are drained out, which results in a stable mine discharge. The stable mine discharge is about 7970m3^{/d, 8240m}3^{/d and 9030m}3^/d for the mining speed of 4m/a, 5m/a and 8m/a respectively. The results of this paper can provide a reference for mining scheme plan and groundwater dynamics monitoring for the similar limestone mining area.