Coupled simulation–optimization model for draining confined aquifer via underground boreholes to prevent water inrush of coal mines

In North China, groundwater drainage is commonly applied by coal mines to prevent water inrush from confined aquifers underlying coal seams, which can also cause environmental problems. The previous research has proposed dual-factor and triple-factor models to manage water resources in coal mines. However, three features of draining confined water via underground boreholes have not been sufficiently considered: the geological heterogeneity, workface relocation, and draining principle of underground boreholes. This paper aims to incorporate the three features into an optimization model for underground borehole draining. A novel mathematical model was proposed that included the three features. A workflow framework was proposed to conduct the optimization based on GIS and a coupled simulation–optimization approach. An algorithm was designed, and a C++ program was developed to couple FEFLOW with a modified genetic algorithm to search for the optimal solution. The application to the Liangbei coal mine indicates that the aquifer has been over-drained. About 69% and 36% of the water could be saved in the first two stages. The total draining rate significantly changes with the workface relocation. The boreholes located at the headwaters and closer to the workface that are mined now or in the next stage usually have higher rates than other boreholes. The distribution of the draining rates is also related to the workface geometry and the aquifer anisotropy. The optimization should be repeated as new monitoring data are acquired.