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Evaluation of Bear No. 3 Mine Landslide <br />Rocky Mountain Geotechnical stated in their report that the "sheaz strength parameters utilized <br />for the bedrock in this particular analysis aze the most conservative parameters which could <br />possibly be obtained." Despite using conservative bedrock parameters the strengths in the rock <br />are significantly higher than the strengths in the colluvium. As would be expected, the limit <br />equilibrium stability analysis conducted by Rocky Mountain Geotechnical produced a series of <br />relatively shallow failure surfaces. The surfaces were either larger radius, shallow circles, or <br />translational sliding blocks with the failure plane near the bedrock colluvial interface. <br />The following quotations from the Rocky Mountain Geotechnical report summarize their <br />interpretation of the sensitivity analysis shown on Figure 9: <br />As may be seen by compazing the results, the stability conditions on this <br />particular site are relatively insensitive to the assumed piezometric conditions. <br />However, there is a relatively high degree of sensitivity associated with the <br />assumed shear strength parameters. <br />If analyzed under residual strength conditions, virtually all slopes containing any <br />significant thickness of colluvial soils (landslide debris) were found to be unstable <br />with theoretical factors of safety less than unity. Under peak shear strength <br />conditions for the colluvial soil, virtually all of these slopes were found to have a <br />condition of marginal stability with factors of safety slightly above unity. <br />A subsequent study prepared by Rocky Mountain Geotechnical titled "Interaction of the <br />Subsidence and Landsliding, Beaz Mine No. 3," evaluated pre-subsidence stability ofdeep-seated <br />bedrock failures for the entire Bear No. 3 Mine permit area. Deep-seated failure surfaces were <br />found to have relatively high factors of safety which "ranged from 1.82 to 5.9 for typical strength <br />parateters" obtained during the investigation. <br />Data from the 1986 Rocky Mountain Geotechnical report was used by WWE to evaluate the <br />stability of a sliding block assuming accumulations of water in the Bear Mine B-Seam workings. <br />Figure 10 presents the information forwarded to CDMG in MCC's Technical Revision No. 80. <br />The stability analysis on the sliding block indicates a factor of safety of approximately 1.9. This <br />factor of safety was calculated by WWE assuming the lowest shear strengths reported in the <br />831-032.411 Wright Water Engineers, Inc. Page 10 <br />