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iviORRISOk•KkUDSEk COi:iPAkY, IlC. <br />Mr. Cass Legal <br />~ ' October 21, 1981 <br />page 2 <br />July 31, 1978, and was prepared by Chen and Associates, Inc., of Denier, <br />Colorado. No borings were drilled in the vicinity of the slope selected <br />for analysis. However, borings were drilled for a settling pond embankment <br />southwest of the slope analyzed. The cohesion and friction angle of the <br />surficial material used for stability analysis of the earthfill embankments <br />were assumed for the analyses of the spoil pile. Consideration was given <br />to reducing these strength parameters. Doing so could not be justified, <br />particularly, since the above-referenced report notes the presence of sand- <br />stone outcrops at the same elevation as the base of the slope analyzed. <br />The analysis performed may be overly conservative in assuming the medium- <br />stiff clay extends to considerable depths below the toe of the slope. The <br />soil strength parameters previously used are believed to be sufficiently <br />conservative for the present purposes. For the long-term condition, the <br />surficial material should increase in shear strength as it consolidates <br />under the load imposed by the spoil above, <br />~ Hydrologic Conditions <br />`-/ For the analyses discussed and reported in the July, 1981 report, it was <br />assumed that no phreatic surface exists within the spoil pile. This as- <br />sumption was based on statements by mine personnel that no seepage has been <br />observed from the spoil pile after a rainstorm, <br />For the more recent analyses, the same slope with the same sets of strength <br />parameters were used, The purpose of these analyses was to determine how <br />high the phreatic surface would have to be to reduce the factor of safety <br />to about 1.5. The results of the analyses indicate that a phreatic surface <br />90 to 110 feet above the toe of the slope would be required to lower the <br />factor of safety to about 1.5. <br />The spoil pile is irregular in shape. At its northeast corner, it is <br />mounded to a maximum elevation of about 7625 feet. The southwest half is <br />generally flat, benched, and about 50 to 15 feet lower. In the event of a <br />\/~ <br />\J~ <br />M133 <br />