2007-08-10_REVISION - M2001107 (4)

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V-METHODOLOGY The mining embankment configuration shown in the computer analysis represents the estimated conditions for this site. If mining conditions differ from the estimated conditions, the slope stability will need to be re-evaluated on a case by case basis. The Bishop Method was used in the computer analysis for determining safety factors. The procedure searches for circular shear failures and automatically searches for the lowest safety factor. 1,000 separate failure surfaces were analyzed for each case. The required minimum safety factors are based on the current standards used by the Colorado State Engineer's Office (SEO) in evaluating embankment dams, and industry accepted standards for the evaluation of temporary structures during construction. VI -SLOPE STABILITY RESULTS The SEO requires minimum factor of safety of 1.25 for static condition analyses and 1.0 for pseudo-static (earthquake loading) condition analyses for Class I (high hazard) embankment dams. This design criteria was used to establish the desired minimum factors of safety for this project and should be considered as highly conservative for evaluating alluvial mining high walls. The calculated factors of safety are within the design criteria specified for this project and can be considered indicators of the high wall performance under the various conditions. The results of the static condition and pseudo-static condition slope stability analyses are presented in Table 2 and Table 3. Table 2 -Static Condition Slope Stability Analysis Results Descri lion Calculated Factor Of Safe Required Minimum Factor Of Safe Case A 1.28 1.25 Case B 1.27 1.25 Case C 1.28 1.25 Case D 1.25 1.25 Case E 1.26 1.25 Case F 1.30 1.25 Case G 1.27 1.25 Case H 1.26 1.25 Rankin Property Gravel Pk Expansion Project Sbpe Stability Analysis Page 4