A new method of analysis of water-level response to a moving boundary of a longwall mine

Longwall coal mining is an economical method for coal extraction that allows most of the coal to be extracted from a wide rectangular panel. The roof of the working face area is temporarily held up by supports which advance as the mine face advances. A basin-like subsidence trough develops at the ground surface over the panel as the panel roof behind the supports collapses. A dynamic subsidence front causes a water-level drop at wells ahead of the panel. We examine the effects of subsidence on water-level by introducing a sink that moves with the mining face, using the one-dimensional flow equation. To test the validity of this method, we estimated aquifer parameters of Trivoli Sandstone aquifer over a longwall coal mine in the Illinois Basin by analyzing water-level versus time data measured from three observation wells. The presented method predicts a value of transmissivity and storage coefficient that is reasonably close to the average of pumping test results. With this method we provide solutions to two significant problems: (1) Presubsidence aquifer parameters that are representative of a large volume of an aquifer can be estimated at minimum cost, and (2) water-level drops can be predicted for a planned longwall mine if the aquifer parameters are known.