THREE-DIMENSIONAL HYDROGEOLOGIC MODELLING OF THE GROUNDWATER INFLOW AT AN UNDERGROUND LIMESTONE MINE IN KOREA

The safety and environmental topics should be addressed for sustainable mining operations, and one of the key issues is a prediction of the groundwater flow into open pit and underground mine workings. Predictions of groundwater inflow require a detailed knowledge of the geologic conditions, including the presence of major faults and other geologic structures at the mine site. The hydrologic boundaries and depth of the phreatic surface of the mine area, as well as other hydrologic properties of the rockmass, are also required. Various numerical models are routinely used to design dewatering systems at mines from an adequate simulation of the groundwater flow. MINEDW by Itasca is one of those groundwater flow model codes developed to simulate the groundwater flow related to mining.

In this study, a 3-D groundwater flow model was constructed using MINEDW to simulate the groundwater conditions at an underground limestone mine in Korea. The study area consists of several Paleozoic limestone formations of varying thickness with intervening dolomite or shale formations, mainly controlled by NW-SE trending westerly overturned folds and thrust faults. These formations and geological structures are horizontally displaced by following NE-SW trending strike-slip faults, resulting in very complex geologic boundaries. The primary purpose of the study was to predict the amount of groundwater inflow and pore-pressure distributions which will affect the stability of the mine workings. As not all information necessary to construct a groundwater flow model were given in detail, some parameters such as the hydraulic conductivity of the rockmass had to be assumed. A calibration was conducted to achieve a reasonable agreement between the measured amount of groundwater inflow with the simulated value. A sensitivity analysis was also performed to find out the most influencing parameter in this groundwater flow modelling.