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<br />bIETHODOLOGY <br />The mining embankment configuration shown in the computer analysis represents the <br />estimated conditions during mining operations for this site. If mining conditions differ <br />from the estimated conditions, the slope stability will need to be reevaluated on a case- <br />by-case basis. <br />T~vo methods were used in the computer analysis for determining safety factors; <br />Simplified Bishop's Procedure and/or JanBu procedure. Both procedures search for <br />circular shear failures and automatically search for the lowest safety factor. Four <br />thousand separate failure surfaces were analyzed for each case. The termination point for <br />the failure surface was forced to pass through the ditch embankment since this is the <br />structure that is within the 200 foot setback and the initiation point was forced near the <br />toe or in the weathered bedrock. The proposed minimum safety factors are based on the <br />current standards used by the State Engineer in evaluating embankment dams. <br />SLOPE STABILITY RESULTS <br />The results of the slope stability analysis are presented in Table 2. The calculated factors <br />of safety are within the design criteria specified for this project and can be considered <br />indicators of the embankment performance under the various conditions. <br />Table 2. Slope Stability Analysis Results <br />Description Factor of safety <br />Constmction condition - JanBu method 1.79 <br />Construction condition -Bishop method 1.77 <br />CONCLUSIONS AND RECCOMENDATIONS <br />The resulting safety factor of 1.78 is above the State Engineers minimum requirement of <br />1.25 for an embankment during construction. The proposed setback of 140 ft. from the <br />centerline of the Brantner Ditch meets the established criteria set by the DMG rules and <br />regulations. <br />The soil properties assumed for this study are extremely conservative. It is our opinion <br />that lab tests would demonstrate that the actual strength parameters would be higher and <br />would result in a safety factor greater than that calculated. <br />