1989-10-10_REVISION - M1988112 (12)

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of safety (FOS) for the critical slip circle associated with • the full height slope is approximately 1.8 for the as- constructed configuration and 2.1 for the reclaimed configuration. The minimum pseudostatic FOS is approximately 1.2 for the as-constructed slopes and 1.4 for the reclaimed slopes. These factors meet required minimums for waste rock dumps of 1.2 and 1.0 specified by the U.S. Forest Service in the March 1989 document titled "Operator Guidelines for Mine Waste Rock Dump Planning Design and BMP's". Thi~r document is a recent document that establishes factors of safety specifically for permanent waste rock disposal locations. The disposal areas also meet the more conservative minimums for water storage, earth, and rack-fill dams specified by the U.S. Army Corps of Engineers (1970) of 1.5 and 1.0 for static and pseudostatic analyses, respectively. The Corps standards were the standards approved in the existing permit and were the only widely accepted standards prior to the Forest Service document, but are more applicable to water storage or impoundment structures. For moderately deep seated slip surfaces associated • with a single bench, the minimum FOS for long-term static and pseudostatic loading conditions are 1.3 and 1.0, respectively for the construction phase and 2.0 and 1.3 respectively, for the long-term reclaimed slopes. The as-constructed and reclaimed factors, exceeded both the USFS minimums and the more conservative U.S. Army Corps of Engineers minimums. The results of analyses for Waste Rock Disposal Area A indicate that the minimum FOS for the critical slip surfaces associated with the full-height slope is 2.1 and 1.4 for static and pseudostatic conditions, respectively. No benches will be constructed for Disposal Area A so the disposal area will be regraded to a 3H:1V outslope during construction. 'f he stability analysis was performed on the reclaimed configuration only since a single bench analysis and an as-constructed analyses D-11