Influence of mining induced subsidence on groundwater resources

An approach is developed to quantify the impact of longwall mining on the potential disruption of groundwater resources. The underlying premise of the method is to assume that the primary mechanism causing dewatering is the development of new fractures or the dilation of existing fractures, as a result of mining induced displacements. From this assumption it is possible to evaluate the potential influence on groundwater resources by; (1) evaluating the anticipated distribution of strain that will accompany mining advance; (2) from this strain distribution, quantify the magnitude and spatial distribution of modified permeabilities; and (3) use this modified hydraulic conductivity field to define changes in the hydrologic budget, thereby defining the potential for, and extent of, any dewatering. Numerical simulation, using the finite element method, is used to both determine the mining induced distribution in strain and to complete hydrologic budget calculations with the revised conductivity field. This approach is applied to mining geometries representative of the eastern United States to define the anticipated sensitivity of these systems to changes in overburden thickness and topography. Results indicate that observed trends in dewatering behaviour may be explained on the basis of zones of contiguous extensile strain, induced within the overburden as a result of mining.