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• 7.0 SUBSIDENCE MODELLING <br />7.1 SELECTION OF ANALYTICAL METHODS <br />A great number of predictive methods are available for use in the <br />analysis of subsidence, all of which were considered for use in <br />this study. Methods considered included the following: <br />1. Empirical methods: these are graphical or tabulated <br />prediction methods, the best known of which is the <br />National Coal Board Method (first published in the <br />Subsidence Engineer's Handbook, 1966, revised 1975). <br />This method was empirically derived from field <br />measurements above a large number of longwall mines in <br />the United Kingdom. <br />• <br />2. Profile functions: these methods are also somewhat <br />empirical in nature and involve the establishment of <br />correlations between mathematical functions which <br />predict subsidence and field observations. These may <br />include either error, exponential, or triginometric <br />functions. However, the most commonly used techniques <br />involve the hyperbolic function. <br />3. Stochastic media: the theory utilized in stochastic <br />methods involves the modelling of a system of tiny <br />spheres as they move to fill a void. Initial concerns <br />. over this method included its inability to accurately <br />13 <br />