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West Elk Mine <br />• relying on the emergency spillway. The individual plan sets in Exhibit 43, Exhibit 47, and <br />Exhibit 66 includes ali pertinent hydrologic and spillway data. <br />Stabi[ity Program Description <br />The stability analysis for the dams was performed using a slope stability computer program <br />(SLOPE II) developed by Geo Slope Programming, Ltd., Regina, Saskatchewan. The Ordinary <br />(Fellenius) Method and the Simplified Bishop Methods were used to compute stability factors of <br />safety for each embankment's maximum cross-section. <br />Both methodologies use the method of slices and utilize the limit equilibrium theory to solve the <br />factor of safety. The principal difference between the two methods is the treatment of interslice <br />forces. The Ordinary Method assumes that interslice forces can be ignored, while the Simplified <br />Bishop Method assumes that the interslice forces act horizontally. Merrick and Company's <br />results indicated that the Ordinary Method yielded lower factors of safety in all cases. <br />Consequently, for all subsequent trials on the given dam, only the Ordinary Method was used. <br />The computer program determines the factor of safety for slip circles of varying radii about <br />specified points but does not automatically converge on the minimum factor of safety. In order <br />to minimize cost, a coazse grid was initially established. The grid was then successively refined <br />to converge on the minimum factor of safety. In most cases three to five interactions were <br />required. <br />Stability analysis for SG-1 was performed using a slope stability computer program entitled <br />XSTABL5.105. The program utilizes Bishops and/or Janbus method for circular or non-circulaz <br />failure. <br />Stability Analysis <br />Various soil states were investigated to determine the most critical condition for each <br />embankment. The unconsolidated undrained condition, the consolidated undrained condition, <br />and the consolidated drained condition were considered for all embankments. In the case of MB- <br />1 and FW-1, for the clay material embankment, the consolidated undrained stability was critical, <br />while for MB-2, the consolidated drained condition was critical. <br />Both a static analysis and a seismic analysis were performed for each dam embankment. For the <br />static analysis a fully saturated embankment was assumed. The seismic (or dynamic) analyses, <br />assuming the same condition, in combination, aze summarized in Exhibit 44. The final run for <br />each analysis is included as a supplement to Exhibit 44. <br />Hvdrologic Protection During Construction <br />Early in construction, prior to the disturbance of any area for surface construction, sedimentation <br />ponds were constructed, and diversion channels to collect undisturbed surface runoff were <br />constructed to meet specific design requirements. These channels were constructed <br />coincidentally with the initial access road, and divert the runoff away from the disturbed areas. <br />2.05.34 Revised June 2005 PR70; Rev. Joriuary 2006; Rev. March 2006; Rev. Apri12006 PRIG, May 2006 PRI G <br />