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Mr. John Poulos • <br />September 27, 1994 <br />Page 2 <br />Based on observations in the field, borehole information, and previous <br />experience in this area, it was concluded that only one failure could occur at this site. <br />The most probable location for this failure would be in the cut slope above the Fan <br />bench. The basis for this observation comes from the fact that bedrock is fairly <br />shallow in this area, as encountered in the recent drill program and observed directly <br />above in the visible outcrops; subsequently, a dramatic failure in the entire slope <br />(including the fan bench) is unlikely since bedrock will probably be encountered, if <br />not fairly close to the surface, during construction of the fan bench. <br />- The thickest wedge of altered non-homogenous colluvium is located in the cut <br />slope above the fan bench. A failure below the fan bench is unlikely because this <br />area will be left in as original or natural condition as feasible. Subsequently, the <br />most probable location for a failure will be in the cut slope above the fan bench. <br />A brief description of the criteria used in the PCSTABL5 program to evaluate <br />the factors of safety for the slope above the fan bench is as follows: <br />Old Slone Geometry: The present slope profile was developed from a 1994 • <br />aerial survey map supplied by Mountain Coal Company. <br />New Slope Geometrv: The proposed one-to-one cut slope for the fan bench is <br />shown on Figure One. <br />_ _ Groundwater: Groundwater was not encountered in a monitoring program of <br />the pizometer installed in borehole #6 in April, 1994. <br />Bedrock: During a recent drilling program conducted on a portion of the fan <br />bench, bedrock was encountered at eight feet below the ground surface. This <br />new information has been incorporated into the stability program. <br />Soil Streneth Properties: Two types of soils were used in the model. The <br />strength pazameters were based on previous strength tests at the site and are <br />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 />• <br />\\ <br />