Ground water flow simulation in mining works: Application of the Hybrid Finite Element Mixing Cell method

Hydrogeological models can greatly help simulating groundwater flow in the particular context of mining works. However, classical modeling techniques are not so suited in this context because the medium is strongly disturbed by shafts and networks of galleries. Consequently, specific modeling techniques have been developed.

Box model techniques require only few parameters but they calculate only mean water levels in exploited zones and do not consider interactions between exploited and unexploited zones. Conversely, physically-based and spatially-distributed techniques represent explicitly both exploited and unexploited zones and take into account interactions between them but they require a lot of parameters sometimes difficult to estimate.

The Hybrid Finite Element Mixing Cell (HFEMC) method is a new modeling technique constituting a compromise between simple and complex techniques used in mining context. The principle of this method is to fully couple a representation of exploited zones by a group of mixing cells possibly interconnected by pipes and a representation of unexploited zones by classical finite elements. Interactions between mixing cells and finite elements of the mesh are taken into account through 3rd type (Fourier) internal boundary conditions. With this method, exploited zones are characterized by mean water levels while spatially-distributed hydraulic heads are calculated for the entire adjacent and overlaying unexploited zones. Additionally, thanks to the coupling between mixing cells and finite elements, water exchanges between exploited and unexploited zones are explicitly taken into account. The HFEMC method allows also simulating groundwater rebound following mine closure and associated phenomena such as water inrushes.

Concepts and equations of the HFEMC method are presented and illustrated using test cases. First results of an application on an abandoned coalfield in the region of Liege (Belgium) are also proposed.