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A'estern Associated Coal <br />May 26, 1982 <br />Page 3 <br />The residual strength conditions produced min€mum fac~ors of <br />safety between 0.77 and 2.2. The thickness of colluvium <br />(measured perpendicular to slope) which willproduce al factor <br />of safety of 1.0, 1.25 and 1.5 was estimated to 'be 13 feet, 10.5 <br />feet, and 8.5 feet, respectively. <br />The peak strength conditions produced minimum f~ctors ofsafety <br />between 0.92 and 2.6. The thickness of co um whicjh will <br />produce a factor of safety of 1.0, 1.25, an 5 was estimated <br />~~ to be 16.5 feet, 13.0 feet, and 10.5 feet respe tively. Results <br />of the slope stability analysis performed are presen ed on the <br />attached tables. <br />CONCLUSIONS AND RECOMMENDATIONS <br />The results of the stability analysis presented above indicate <br />that the modeled conditions vary between unstable to very stable <br />(indicated factors of safety between approximately 0.77 and 2.6) <br />depending on the thickness of colluvium in relationship to the <br />excavated section of the access road. <br />Our experience in the area has been that virtu~lly all uts in <br />the access road are founded in the bedrock. The slope s~bility <br />model utilized in this analysis is predicated on that assumption. <br />Based on the results of our analysis, we feel a moderate to very <br />stable condition will exist wherever excavations penetrate a <br />thickness of not more than 13 feet of colluvial soil (measured <br />perpendicular to the slope face). <br />If exceeding the maximum depth of colluvium cannot be avoided, we <br />would recommend that the excavated slope be flattened as close as <br />possible to approximate natural slope conditions or other methods <br />of shoring the slope be utilized. <br />We trust that the information presented in this report is <br />sufficiently detailed to satisfy your needs and permit proper <br />review and approval by the State and Federal regulatory agencies. <br />If you require additional information or clarification of the <br />results presented, please contact us. <br />Respectfully submitted, <br />ROCKY MOUNTAIN GEOTECHNICAL <br />~~d <br />Richard JF <br />Project Erb <br />RJG/sam <br />Gre"enygp~Ct;; "i~ <br />in~ei `<~~- <br />~~~_. c.... E' <br />`, , <br />enR~ -ne h M e s <br />Principal in Ch ge <br />