Subsidence Associated With Single and Multicavities for Underground Coal Gasification

The three-dimensional theoretical development of Berry and Sales [1] has been extended to bring the subsidence predictions into agreement with the British National Coal Board comprehensive set of empirical data. New elastic parameters have been determined to fit the amplitude of the ground level subsidence. An empirical correction factor was developed to account for small cavity width-to-depth ratio cases. This correction is believed to account for incomplete closure for half width-to-depth ratios below 0.3. The theory has also been modified to bring the subsidence profiles into agreement with the foregoing referenced data. The development has been used to predict subsidence for an actual U.S. coal mining case with multiple cavities. The theory was also used to predict subsidence level and profile for a recent Gulf/DOE UCG test conducted in a steeply dipping coal seam near Rawlins, Wyoming.