Application of the HFEMC method to an abandoned coalfield in Belgium: From conceptualisation to scenario simulations

The Hybrid Finite Element Mixing Cell (HFEMC) method is a flexible modelling technique particularly suited to mining context (Brouyère et al., 2009). The principle of this method is to subdivide the modelled zone into several subdomains and to select a specific equation, ranging from the simple linear reservoir equation to the groundwater flow in porous media equation, to model groundwater flow in each subdomain. The model can be run in transient conditions, which makes it a useful tool for managing mine closure post-issues such as groundwater rebound and water inrushes.
An application of the HFEMC method to an abandoned underground coal mine near the city of Liège (Belgium) is presented. The case study zone has been discretized taking advantage of the flexibility of the method. Then, the model has been calibrated in both steady-state and transient flow regimes based on hydraulic head and water discharge rate observations. Finally, the calibrated model has been used to run several scenarios in order to assess the impacts of possible future phenomena on the hydraulic heads and the water discharge rates. Among others, the simulation of a strong rainfall event shows a quick and strong increase in hydraulic heads in some exploited zones coupled with a strong increase in associated water discharge rates. This could lead to stability problems in the hill slopes near the exploited zones. This kind of predictions can greatly help managing and predicting mine water problems in this particularly complex mining system.