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British Coal belongs to the Carboniferous period while the coal in Colorado is of the <br />Cretaceous Age ( Mesaverde Formation). Mesaverde Formation rocks are generally harder <br />than overburden rock found in Britain. This is probably why observed subsidence <br />magnitudes tend to be lower in the U.S. than subsidence predicted using the SEH, as <br />described by Hall and Dowding (1981). Similarly, the subsidence profile tends to be <br />narrower, limit angles are steeper, and the risk of subsidence cracks appearing at surface <br />is probably greater in the U. S. <br />There is no way of taking account of varying geological conditions using the SEH. <br />Since the predictions have been developed based on observations under British <br />conditions, the method should be used for predicting subsidence in the U. S. only with <br />considerable caution and a thorough understanding of its basis and limitations. <br />Empirical Equations: <br />These include influence functions, in which the principle of superposition is used to <br />sum the effects of the various elements which comprise an extraction area, and profile <br />functions, in which a mathematical equation, generally a hyperbolic function, is used to <br />describe the subsidence profile. These are described in detail by Brauner (1973). <br />In theory, empirical equations have the advantage of being able to include <br />parameters which represent the characteristics of the overburden strata. In practice, little <br />guidance and experience is available in the selection of these parameters. The method <br />therefore offers little advantage over using the SEH in most practical cases. <br />Significant limitations are inherent in all subsidence prediction methods when <br />applied to areas and geological conditions where there is little or no previous experience in <br />subsidence prediction. Realistic estimates of subsidence can be made, although the <br />accuracy of the prediction will be less certain than that of estimates made in areas where <br />there has been adequate documentation of previous subsidence. By considering past <br />experience with the model used, it is possible to make a best estimate of subsidence as <br />well as to estimate limits within which the actual subsidence should lie. <br />After consideration of the limitations inherent in the alternative methods available for <br />subsidence prediction, the SEH method has been selected as the principal method for <br />subsidence prediction at the Bowie #2 Mine. Its application has been modified, where <br />appropriate, to account for the specific geotechnical and mining conditions at the mine. <br />PR -14 - 2 - 03/14 <br />