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Conservative application of Piggott and Eynon's (1977) worst -case conical chimney <br />height prediction method indicates that even a worst -case conical chimney collapse should <br />not breach more than 110 foot of overburden under normal geologic conditions. <br />Conical chimney collapse height (H) Piggott and Eynon (1977) <br />Sandstone overburden <br />H _ 3(h)(100) <br />%S <br />H= 3(9.5)(100) <br />67 <br />H=42 ft. <br />Shale overburden <br />H _ 3(h)(100) <br />%S <br />H _ 3(9.5)(100) <br />33 <br />H = 86 ft. <br />Gray, Bruhn and Truka (1977) physically documented the height of collapse <br />chimney subsidence above the Pittsburgh Seam for 127 cases. Gray, et. al. reported <br />chimney subsidence height without respect to the actual mining height or the lithology. Six <br />of the 127 cases breached the ground surface 110 feet above the Pittsburgh Seam. Table <br />15 -3 presents the relative cumulative frequency distribution for their data. Gray's (1977) <br />chimney data from the Pittsburgh Seam indicates that a chimney has a minor, <br />approximately 4.7 percent, potential to penetrate 110 feet of overburden. <br />The Bowie #2 Mine mining activities should be in overburden thickness greater than <br />110 feet. Therefore, it is unlikely that chimney collapse will penetrate to the surface above <br />the mine workings. <br />PR -14 -16- 03/14 <br />