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Sanborn Creek Subsidence Page 95 September 2, 1997 <br />CONCLUSIONS <br />The ground surface over and near the planned B Seam longwall <br />panels will subside. The surface subsidence will be of the type <br />referred to as trough subsidence. Chimney subsidence that may <br />,. take place in the planned longwall panels and gateroads will not <br />breach the ground surface. The possibility of chimney subsidence <br />breaching any of the overlying workings, either the Oliver No. 1 <br />Mine 238-ft overhead or the Hawksnest Mine 364-ft overhead is <br />extremely remote. The predicted worst-case lowering of the <br />overlying ground surface by the subsidence accompanying longwall <br />panel mining exceeds 11-ft as an absolute maximum. It is probable <br />that actual maximum surface subsidence will not exceed 9-ft. The <br />maximum predicted horizontal tensile strains at the ground surface <br />will result in open surface fractures. The width of these open <br />fractures will range from a small fraction of an inch (tensile <br />strains in the range from 1000µe to 3000µe) to nearly a foot in <br />width (tensile strains of about 9000µe). The magnitude of the <br />maximum predicted compressive strains at the ground surface range <br />from undetectable to compression ridges approaching 1-ft in <br />~~ height. <br />It is probable that the longwall mining induced trough <br />subsidence strains in the interburden between the planned Sanborn <br />Creek Mine B Seam longwall panels and the overlying abandoned <br />Oliver No. 1 Mine workings in the D Seam 238-ft overhead will be <br />sufficient to progressively drain any impounded water. The same <br />is true for the overlying abandoned Hawksnest Mine workings, in <br />r the E Seam 369-ft overhead. There are no known channels for rapid <br />._ movement of water from overlying mine workings and the Sanborn <br />Creek Mine. It is not known whether water is actually present in <br />the old workings in either mine. <br />R potential landslide has been indicated over Panels #5 - #7 <br />by the USGS. There is no obvious evidence at the ground surface <br />of the indicated potential landslide. The stability of the <br />L potential landslide should be slightly improved by the subsidence <br />accompanying longwall mining of Panels #5 - #7. The minor slope <br />stability improvement is the result of the location of the panels <br />- and, therefore, the maximum subsidence under the center of the <br />potential landslide. The geometric conditions result in trough <br />subsidence tilting of the south-facing hillside backward into the <br />•- slope. The minor improvement in slope stability will occur <br />regardless of the whether the potential landslide is actually <br />L present. <br />~~ <br />L 45 <br />