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• Kathy Welt <br />August 31, 1994 <br />Page 2 <br />The forces which tend to cause failure include; but are not limited to: (a) the angle <br />of the slope; (b) the location of existing haul roads and drainage ditches in relation <br />to the slope; (c) pore pressure or water table acting on the failure plane; and (d) the <br />characteristics of the native soil and bedrock found in the slope. A factor of safety <br />of 1.0 implies that the slope is marginally stable for the cross-section profiled, native <br />clay material strengths, groundwater, and the slope conditions. In designing the <br />pile, Envirocon has used a minimum factor of safety of 1.5, as required by the State <br />of Colorado Mined Land 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 Slope Geometry: The present slope profiled 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 have been previously <br />submitted. <br />• New Slone Geometry: The proposed fill profile for the Mine development waste <br />pile is shown on drawing LPG - 103F, Lone Pine Gulch Fan /Portal Bench <br />design. <br />Soil Streneth Properties: Various types of soils (one modified by compaction) <br />are used in the model. The strength parameters of the soils are based on <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 />Bedrock - Cohesion 7500 psi, internal friction angle 0°, moist <br />unit weight 150 pcf, saturated unit weight 150 pcf. <br />Mine Development Waste Pile - Cohesion 288 psi, internal <br />friction angle 30°, moist unit weight 80 pcf, saturated unit weight <br />90 pcf. <br /> <br />~,=a <br />