2010-10-22_REVISION - M2008017 (4)

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Table 1 - Soil Properties Description Max dry density c Saturated Density c Cohesion s Internal Friction Angle Slur Wall 62.4 62.4 0 60 Sand and Gravel 110 125 0 35 Weathered Bedrock 125 141 100 18 Stable Bedrock 125 141 2000 20 DESIGN ANALYSIS AND CRITERIA The proposed mining slopes were analyzed using the XSTABL v5.105a computer program. XSTABL was designed to analyze the slope stability of earth embankments subjected to several critical situations that may occur during the life of the embankment. For Technical Revision No. 1, four cases were identified as critical during the mining operation. Static and pseudo-static conditions were analyzed for each case, for both wet mining and dewatered vertical slope configurations. Pseudo-static peak acceleration factors were taken from USGS information for the western United States. The 2% probability of exceedance in 50 years (the most conservative) was used. Surface loading equivalent to an HS 20 highway load was applied adjacent to each area to simulate heavy equipment loading that could be present at that location for maintenance or construction activities. The revised interim mining side slopes will be vertical during wet mining and 3H:1 V after the slurry wall is installed and the pit is dewatered. Only the interim mining vertical slopes are analyzed in this report as the final mining 3H:1 V slope configurations were analyzed and approved in the slope stability report submitted with the original permit application. Case 1a - South Property Line (SOUTH 1a). The mining operation is adjacent to a private property on the south side of the site. The mining depth was assumed to be 85 feet in this area based on bore log information in the geotechnical reports. The proposed interim setback for mining is 120 feet from the final mining limit (170 feet from the property line). Case 2a - Existing Balsam Avenue ROW (WEST 2a). The mining operation is adjacent to Balsam Avenue on the west side of the site. The mining depth was assumed to be 75 feet in this area based on bore log information in the geotechnical reports. The proposed interim setback for mining is 90 feet from the final mining limit (130 feet from the existing ROW). Broken Arrow Investments, LLC - Derr Pit - M-2008-17 J&T Consulting, Inc. Technical Revision No. 1- Slope Stability Analysis ia, Page 2