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1 <br />' Harding Lawson Associates <br /> September 14, 1995 <br />32640.5 <br /> Mr. Norm Every <br /> Mountain Coal Company <br />' Page 2 <br /> wall. Four slope stability analyses were modeled (refer to Figures 3 & 4) To fully understand the mechanism of <br /> the rotational slump. The first series of analyses modeled the original slope with the soil failure incorporated <br />' into the model. The second series of analyses models a soil butVess design that mitigates further erosion of the <br /> present failure and acts as a support for [he rebuilding of the mine portal access road (refer to Figures 5 & 6). <br />' A brief description of [he criteria used in the PCSTABLS program to evaluate the factors of safety for the <br /> proposed soil buttress design are as follows: <br /> <br /> <br />1 <br />1 <br /> <br />1 <br />1 <br />Present Failure Geometry: The present slope pro5le(s) and mine portal access road was developed from <br />an overall map of the mine site (refer to Figures 3 & 4). <br />Proposed Buttress Geometry: The proposed soil buttress design incorporates the present slope with the <br />current soil failure (refer to Figures 5 & 6). <br />Groundwater: Groundwater levels in this study is assumed [o be located on the slope surface as observed <br />in the field during the early spring late winter thaw. The slope stability analysis assumes a high <br />groundwater level in all models. <br />Soil Syencth Properties: Four soil types were used in the model. The svength parameters were based on <br />previous strength tests at the site and are as follows: <br />- Compacted pit-run: Pit-run gravel, cohesion 0.0 psf, internal fiction angle 35.0 degrees, moist <br />unit weight 130.0 pcf, saturated unit weigh[ 135.0 pcf. <br />- Colluvial Soil: Low plastic clay, cohesion 437.00 psf, internal friction angle 19 degrees, moist <br />unit weight 130.0 pcf, saturated unit weight 135.0 pcf. <br />- Bedrock: Mesa Verde Sandstone group, cohesion 7500 psf, internal friction angle 45 degrees, <br />moist unit weight 150.0 pcf, saturated unit weight 150.0 pcf. <br />- Bin Wall: Metal frame work with soldier beams, cohesive 0.0 psf, internal friction angle 30.0 <br />degrees, moist unit weight 150.0 pcf, saturated unit weight 150.0 pcf. <br />The input information for the analyses includes slope geometry, groundwater conditions, soil strengths, and <br />loading conditions (refer to appendis for slope stability calculation sheets). <br />Factor of safety results of the stability analysis for the profiles below the bin walVmine portal access road is as <br />follows: <br />Profile A:A Prof le B:B Profile C:C Profile D:D <br />Present Slope Failure 0.85 0.84 0.83 0.91 <br />Sail Buttress Design 1.43 1.49 1.70 1.68 <br />