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"D" Seam Longwall Subsidence Page 7 August 17, 1998 <br />• Table 2 presents the interburden thickness lithology <br />distribution indicated by borehole logging. The approximate <br />199-foot thickness of the interburden and the approximate weighted <br />average 61$ sandstone in the interburden between the "D" Seam and <br />the underlying "C" Seam should be sufficient to prevent adverse <br />mining induced stress concentrations during planned "D" Seam <br />longwall mining. The approximate 238-foot thickness of the <br />interburden and the approximate weighted average 58$ sandstone in <br />the interburden between the "D" Seam and the underlying "B" Seam <br />should also prevent adverse mining induced stress concentrations <br />during planned "D" Seam longwall mining. <br />Table 2. Approximate interburden spacings and lithologic <br />distributions between coal seams. <br />Borehole Shale Sandstone Coal Total <br />Ident. ($ in ($ in ($ in Interburden <br />section) section) section) Thickness <br />(feet) <br />• <br />WSC-1 <br />28.5$ "D" Seam to "C" <br />70.9$ Seam <br />0.6$ <br />192.1 <br />WSC-2 40.8$ 59.2$ 0.0$ 188.5 <br />WSC-4 44.0$ 54.3$ 1.7$ 199.3 <br />WSC-7 ----- ----- ----- 195.0 <br />Mean 37.8$ 61.5$ 0.8$ 193.7 <br />Std Dev 8.2$ 8.5$ 0.9$ 9.6 <br /> "D" Seam to "B" Seam <br />WSC-1 34.7$ 64.8$ 0.5$ 233.4 <br />WSC-2 ?34.5$ ?50.0$ ?0.0$ 223.1 <br />WSC-4 40.7$ 58.0$ 1.3$ 253.6 <br />WSC-7 ----- ----- ----- 241.7 <br />Mean ?36.8$ ?57.7$ ?0.6$ 238.0 <br />Std Dev 2.9$ 5.9$ 0.5$ 12.9 <br /> <br />7 <br />