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ICI <br />In the West Pit the design Factor of Safety ranges from 2 near the face to 1.5 <br />at deeper auger penetrations. These factors of safety are for overburden and spoil <br />height conditions anticipated during auger mining. After auger mining, the effects <br />of covering the mined area with spoil will decrease the factors of safety. The areas <br />most affected are (Fig. A-1) the eastern portion of Area 1, Area 2 and the northern <br />portion of Area 3. In these areas the factors of safety for pillars is estimated to be <br />reduced from 1.5 to 2 to a range of 1.2 to 2. Even where the lower factors of safety <br />exist, a considerable area of total pillar failure would be required to propagate a <br />significant effect to the surface of the spoil pile. We believe this is very unlikely for <br />the deeper mined seams (C, D or E). If pillars in the X-seam were to fail, subsidence <br />at the top of the bedrock on the order of 2 to 3 feet could occur. The areas where <br />the lowered factors of safety occur are also where the excess spoil is the thickest. <br />For a spoil thickness of 300 to 400 feet and an estimated settlement of 4 to 6 percent <br />under Rs own weight, settlement of the spoil on the order of 12 to 24 feet is <br />considered possible without angering. In the unlikely event subsidence due to X- <br />. seam pillar failure occurs, the surface effects when compared to the effects due to <br />normal spoil settlement will be negligible. <br />STABILfTY ANALYSES <br />Stability analyses of the north wall of the West Pit were performed. We also <br />developed recommendations for the east and west walls of the initial box cut. The <br />analyses were performed to evaluate various overall slope angles and consider the <br />effects of spoil pile location. At the north wall favorable bedding conditions are <br />anticipated. The rock bedding will dip into the slope on the order of 5 degrees. The <br />slope is oriented close to perpendicular to the dip which should result in joints near <br />parallel to the face. This is the most favorable orientation. Along the east and west <br />sides of the box cut conditions are considered favorable with the bedrock near flat <br />lying; neither dipping into or out of the face to a significant degree. The slope <br />heights along the sides will be higher than the north wall due to a closer distance to <br />• the X and Y-Seam excavations. Two primary methods were used to evaluate <br />conditions: <br />COLOWVO COAL COMPANY, L. P. <br />OTU'f 2J.595 11 <br />