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<br />1. Wedge Analysis. In this model the structure controls the orientation <br />of the failure surface and a low strength associated with clay or shale <br />joint filling is used. This method was used by Wahler in the original <br />investigation'. Wahler used very conservative water assumptions, <br />essentially saturation of each interburden above the coal seams. We <br />used this model to evaluate more favorable dip conditions and also <br />more favorable water conditions using saturation of each overburden <br />to 1/2 the interburden thickness. <br />2. Circular Analysis. In this model the failure surface location is not <br />controlled by the rock structure and an overall rock mass strength is <br />assumed. Water conditions were again improved to simulate <br />saturation of 1/2 of each interburden height. Two methods were used <br />to estimate the rock mass strength envelope, including a rock mass <br />rating system and back-calculation from a successful working face <br />configuration. <br />In our opinion, the slopes will perform in a manner intermediate between the <br />wedge and circular models. The following sections discuss the results of each <br />method of analysis and a summary of the results and recommendations. Related <br />• figures are presented in Appendix B. <br />Water and Pseudostatic Conditions <br />A pseudostatic horizontal acceleration factor of O.OSg was used in some <br />models to consider the effects of blasting/ground movement. Two generalized water <br />conditions were modelled. The most conservative is saturation of each interburden <br />between each coal seam to the full height, this condition is referred to on figures as <br />full water. In our opinion, a more realistic but still conservative condition is <br />saturation of each interburden to 1/2 height. <br />Wedge Analysis <br />Wahler used a similar method to evaluate stability in the original pit slope <br />investigation'. The Wahler analysis included a slope height on the order of 330 feet, <br />saturation of the interburden between each coal seam, and a strength envelope <br />• defined by ~ = 24.2' and C = 4 psi. This strength is relatively low and was <br />based upon average total and effective envelopes from tests on clay and <br />COLOWYO COpL COMPgNY, L P. <br />CTUT 27,585 12 <br />