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• existing data on subsidence phenomena related to pitching seam mining <br /> indicate that the angles of draw on the up-dip and down-dip sides of the <br />mined out area are not symetrical (National Coal Board, 1975; and, Mood- <br />ruff, 1966}. <br />It is estimated that the draw angles at the North Thompson Creek Mines <br />will exhibit this skewed distribution. Up-d 1p draw angles probably will <br />not exceed 35'. Down-d 1p draw angles probably will not exceed 45'. <br />These predictions are based on an interpolation of the National Coal <br />Board (NCB) data (National Coal Board, Fig. 8, 1975). These predictions <br />agree well with the results of a preliminary finite element model devel- <br />oped to predict rock mass response to longwall mining at the No. 1 Mine <br />(Kripakov, 1981). <br /> <br />It 1s believed that these selected draw angle values ere conservative <br />and effectively define the outer envelope of possible draw angles that <br />may result from mining at the North Thompson Creek Mines. Various re- <br />searchers have Indicated that NCB data produce conservative draw angle <br />values when applied to overburden sections containing the thick sand- <br />stone beds that are a characteristic of coal fields in the western <br />United States (King, 1960; Abel and Lee. 1980; and, Kapp, 1974). <br />The magnitude of the maximum subsidence that may dCCUr from full extrac- <br />tion mining is a function of: <br />1. extracted seam height <br />• 2. width of the mined out area <br />3. depth of overburden cover <br />17 <br />