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• 5.0 SUBSIDENCE PREDICTIONS <br />5.1 BACKGROU[JD OF PREDICTIONS <br />Tie theories for predicting subsidence caused by coal <br />extraction apply to wide openings with total extraction and <br />have been developed from observations above long wall panels. <br />however, if pillars are completely recovered in room-and- <br />pillar mining, the result is total extraction and the same <br />theories should be applicable. <br />Subsidence prediction methods can be divided into two <br />categories: the empirical and the phenomenological <br />approaches (Hall and Dowding, 1981). Empirical methods <br />predict subsidence based on previous experience and <br />observations under similar geological and mining conditions. <br />Phenomenological methods model the physical behavior of the <br />earth materials using physical or numerical methods in order <br />to predict subsidence. Empirical methods are generally used <br />for the practical prediction of subsidence. With <br />phenomenological models, it is invariably difficult to <br />accurately represent the complex geologic conditions and <br />rock mass characteristics which are ini~erent to underground <br />coal mines. The models available are continually being <br />further refined in research projects and find limited <br />• application in specialized problems. <br />In accordance with most practical subsidence <br />investigations, empirical methods of prediction have been <br />used for this study. The two most commonly used empirical <br />methods of subsidence prediction are as follows: <br />Subsidence Engineers' Handbook (SEH <br />The Subsidence Engineers' Handbook (1975) has been <br />developed by Britain's National Coal Board based on <br />extensive monitoring of subsidence in Great Britain. It <br />comprises perhaps the most complete method to deal with all <br />aspects of subsidence engineering and it has been widely <br />used in different parts of the world. The graphical <br />solutions presented in this handbook are reported to have an <br />accuracy of t 10€ when used in Great Britain. <br />British coal belongs to t}~e Carboniferous period while <br />the coal in west Colorado is of the Cretaceous Aqe <br />(Mesaverde Formation). Mesaverde Formation rocks are <br />generally harder than overburden rock in 6ritain. This is <br />probably why observed subsidence magnitudes tend to be lower <br />in the U.S. than subsidence predicted using the SEH, as <br />`J <br />- 26 - <br />