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2004 Geobgic Hazard Field Observations <br />South of Divide Mining Area <br />• <br />Panels El to E8: For the eight panels (panels El-E8) projected horizontal tensile strain <br />ranges from 0.004 to 0.022 (0.4 to 22 percent) where the planned coal extraction thickness <br />(t) is 8 feet; from 0.007 to 0.027 (0.7 to 2.7 percent) where the extraction thickness equals 12 <br />feet; and from 0.007 to 0.039 (0.7 to 3.9 percent) where the extraction thickness equals 14 <br />feet Maximmn tensile strain of 3.9 percent is expected to occrn- within the area of mining <br />influence above the western limit of longwall panels E2 and E3, should 14 feet of wal be <br />extracted. <br />• Horizontal compressive strain varies from -0.004 to -0.024 (-0.4 to -2.4 percent) where t <br />equals 8 feet; -0.007 to -0.029 (-0.7 to -2.9 percent) where t equals 12 feet; and -0.007 to - <br />0.042 (-0.7 to ~.2 percent) where t equals 14 feet (Table 1). <br />Panel E9: Horizontal tensile strain Predicted above this single panel ranges from 0.018 <br />0.027 (1.8 to 2.7 percent), where the coal extraction thickness equals 12 feet, and 0.021 to <br />0.031 (2.1 to 3.1 percent) where the extraction thickness equals 14 feet Maximum tensile <br />strain percent of 3.1 percent is expected within the area of mining influence of the northern <br />limit of longwall panel E9 in the landslide area. <br />• Horizontal compressive strain in this panel varies from -0.018 to -0.029 (-1.8 to -2.9 percent) <br />where the extraction thickness equals 12 feet and -0.021 to-0.034 (-2.1 to -3.4 percent) where <br />t equals 14 feet (Table 1). <br />7.2 Maximum Projected Depths of Surface Cracks <br /> <br />In areas where coal is extracted by the longwall method, all the coal is extracted within the <br />longwall panel The surface and rocks above the longwall panels therefore undergo <br />downwarping as multiple plates, or layers, in three dimensions, or beams in two dimensions. <br />Under this oonceptttal model, which in the author's opinion (based on field observations) is a <br />valid concept, ao surface water can flow a vertical distance greater than the depth of the neutral <br />surface (the surface where tension above becomes compression below). This vertical distance <br />831-032.621 Wright Water Engineers, Ina Page 15 <br />November 2004 <br />