2008-11-20_PERMIT FILE - M2008078 (2)

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IV - DESIGN ANALYSIS AND CRITERIA The proposed mining slopes were analyzed using the XSTABL v5 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. Static and pseudo-static conditions were analyzed in each case. 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 loads equivalent to an HS 20 highway load or an or an HS 80 railroad load were applied adjacent to each area, when applicable, to simulate heavy equipment loading that could be present at that location. For this project, seven cases were identified as critical during the mining operation: Case A - Existing Prowers County Road HH.5, existing underground telephone line, and existing underground gas line to the south. The mining operation is adjacent to numerous man made structures in this area. The proposed setback for mining is 60 feet from the proposed permit boundary, and 70 feet from the edge of the existing County Road HH.5. The mining depth was assumed to be 44 feet in this area based on bore log information in the JAC report. The mining side slope in this location will 0.5h:1v. Case B - Proposed railroad corridor to the west. The mining operation is adjacent to a proposed railroad corridor in this area. The proposed setback for mining is 35 feet from the proposed permit boundary, and 65 feet from the proposed railroad corridor. The mining depth was assumed to be 51 feet in this area based on bore log information in the JAC report. The mining side slope in this location will 0.5h:1v. Case C - Existing overhead power line to the north. The mining operation is adjacent to an overhead power line in this area. The proposed setback for mining is 80 feet from the existing overhead power line. The mining depth was assumed to be 67 feet in this area based on bore log information in the JAC report. The mining side slope in this location will 0.5h:1 v. Case D - Existing parcel reserved for future highway infrastructure to the west. The mining operation is adjacent to an existing parcel reserved for future highway infrastructure in this area. The proposed setback for mining is 85 feet from the parcel. The mining depth was assumed to be 71 feet in this area based on bore log information in the JAC report. The mining side slope in this location will 0.5h:1v. Case E - Existing irrigation ditch to the south. The mining operation is adjacent to an existing irrigation ditch in this area. The proposed setback for mining is 80 feet from the closest irrigation ditch bank. The mining depth was assumed to be 63 feet in this area based on bore log information in the JAC report. The mining side slope in this location will 0.5h:1 v. Case F - Existing conservation easement to the west. The mining operation is adjacent to an existing conservation easement in this area. The proposed setback for West Farm Gravel Pit Slope Stability Analysis Page 2