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eh <br />ESPEY, HUSTON 8 ASSOCIATES, INC. <br />C~ <br />2.0 EXPECTED EFFECTS OF SUBSIDENCE <br />There is no site-specific field information available on the effects of <br />subsidence for multiple seam mining operations on steeply dipping coal seams in the <br />western United States. Therefore, it is very difficult to predict exactly what <br />effects the subsidence will have on the surface. <br />A very intense, well-documented study on the effects of subsidence from <br />longwall mining was performed by the U.S. Bureau of Mines at the York Canyon <br />Mine near Raton, New Mexico. In the azea of study, the coal seam thickness varied <br />from 15 to 20 feet, the mining height was 10 feet, and the bed dipped approximately <br />2 degrees. Results showed that topography strongly influenced the magnitude and <br />distribution of subsidence and that the angle of draw (average 15.5°) decreased on <br />topographic lows. Underground mining activity produced almost an instantaneous <br />surface movement which ceased as soon as mining was completed. Residual settling <br />I over the panels was minimal. Surface cracks were the only visible manifestations of <br />the subsidence, and most of these will close in time. Panels which were caved very <br />close to the steep hillside, with the face paralleling the hillside caused large <br />horizontal cracks to develop on the face of the slope. Because of the steep slope <br />and orientation of the cracks, they will never completely heal. <br />Northern Coal Company expects the general results of the subsidence to <br />be similar to that experienced at the York Canyon Mine. The angle of draw should <br />be between 12° and 16° and a lowering of elevation in some areas will be <br />approximately 11 feet. While the caving is proceeding, there will be tension and <br />compression waves detectable on the overlying surface, but once the subsidence is <br />complete, final results will be a general lowering of the area with the possibility of <br />some fractures and cracks in the transitional area from subsided to non-subsided <br />ground. <br /> <br />S-3 <br />