Study of karst groundwater flow characteristics of a mine in Pingnan county, Guangxi through connection test

The mine in Pingnan county, Guangxi is located in a closed hydrogeological basin which borders the Qinchuan River in the east, the Xunjiang River in the south, the Wujiang River in the west and the watershed of groundwater in the north. The strata exposed in the mine area are mainly Devonian limestone and calcite dolomite, and Quaternary Holocene loose deposits. Declining groundwater levels due to artificial drainage lead to a redistribution of the groundwater flow field and the mining area became a cone of depression in the aquifer. The Qinchuan River is a potential risk to mining safety. In order to understand the flow path and percolation velocity of groundwater, and recharge sources of drainage water in the mine area, a connection test was conducted. The results of the connection test indicated that the medium of aquifer was highly heterogeneous and anisotropic because there was a huge difference in permeability between test sections. Moreover, the northern and eastern connectivity was better than that of the southern one. Groundwater velocity ranged from 0.3 to 20 m/h in the north and ranged from 3.72 to 98 m/h in the east. There is a groundwater watershed between the mine area and Xunjiang River, so the hydraulic connection of mine in the south and the periphery was weak. Therefore, the lateral runoff in the north and the leakage from the Qinchuan River were mainly recharge sources of groundwater in the first mining area based on the connection test results. In addition, except the lateral runoff in the north, local precipitation was the main recharge source for groundwater in the second mining area. Finally, in order to choose an appropriate time to drain groundwater, fluctuations in the level of Qinchuan River should be recorded and analyzed from a security perspective. On the other hand, some engineering measures should be considered to block groundwater flow, such as curtain grouting anti-seepage.