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• Mrs. Kathy G. Welt <br />August 9, 1994 <br />Page 2 <br />minimum factor of safety of 1.3, as required by the State of Colorado Mined Land <br />Reclamation Board, 1991. <br />A brief description of the criteria used in the PCSTABL5 program to evaluate <br />the factors of safety for each pile is as follows: <br />Old Slone Geometry: The present slope profiles were developed from a 1994 <br />aerial topography map supplied by Mountain Coal Company. <br />Groundwater: Groundwater was assumed at the depths noted on the drilling <br />logs from the April 1994 exploration work. These logs are attached with these <br />letter. <br />New Slone Geometry: The proposed cut and fill profiles for the bench and the <br />various piles are shown on drawing LPG - 103F, Lone Pine Gulch Fan J Portal <br />Bench design. <br />• Soil Strength Properties: Various types of soils (one modified by compaction) <br />are used in the model. The strength parameters of the soils are based oa <br />previous strength tests at the site, and are as follows: <br />• Native Colluvial Soil -Low plastic clay, cohesion 432 psf, internal <br />friction angle 25.4°, moist unit weight 124.1 pcf, saturated unit <br />weight 135 pcf. <br />• Compacted Native Colluvial Soil -Low plastic clay, cohesion 2000 <br />psf, internal friction angle 0°, moist unit weight 124.1 pcf, <br />saturated unit weight 135 pcf. <br />• Topsoil -Cohesion 1600 psf, internal Friction angle 29°, moist unit <br />weight 94 pcf, saturated unit weight 117 pcf. <br />• Bedrock - Cohesion 3400 psi, internal friction angle 0°, moist <br />unit weight 150 pcf, saturated unit weight 150 pcf. <br />Slope stability was evaluated using PCSTABL5. This computer program was <br />developed at Purdue University and uses the simplified Janbu or simplified Bishop <br />method of slices. It compares the forces resisting slope failure to forces which cause <br />• slope failure along a specified failure surface. The analysis utilizes a limit <br />