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. 5.0 PREDICTED GROUND MOVEMENTS <br />5.1 Methodology <br />Surface subsidence is the readily observable manifestation on the ground surface of <br />the displacement field surrounding the underground portion of the mine. Predicting <br />subsidence magnitude, therefore, constitutes a particular solution of the overall problem <br />of finding the induced displacement field. To study subsidence phenomena and estimate <br />the magnitude of subsidence, a number of empirical, physical, and numerical methods <br />have been used. <br />Empirical methods, including profile functions, influence functions, and graphical <br />methods were proposed by the British National Coal Board. These methods involve the <br />analysis of existing subsidence from an area to predict future subsidence effects. These <br />methods are based on the mathematical fit of a considerable number of measured <br />is subsidence profiles. They apply to geologic conditions in the area where they were <br />developed and require adjustments if they are applied to different strata conditions. <br />To estimate surface deformation above the proposed longwall panels, we used a <br />three-dimensional influence function method while accounting for site-specific <br />conditions using the subsidence monitoring data from BRL. These methods have become <br />very popular for the prediction of subsidence and surface strains within the last two <br />decades (USBM, 1983; Peng and others 1994; SDPS 2000). They are superior to <br />graphical methods because they can be used to model an entire longwall block while <br />allowing an examination of the sensitivity of results to variations in seam thickness, pillar <br />designs, panel dimensions, and overburden thickness. <br />These methods rely on the influence of an extracted volume on the displacement <br />components of a remote point on the surface. In the zone calculation method, for <br />example, the circular zone of influence around a point on the ground surface is divided <br />into a number of zones in such a manner that the influence factor of such an area is fixed <br />i <br />Maleki Technologies, Inc. Page 29