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shear testing was performed on material passing through the #4 sieve to minimize effects from the <br />gravel. <br />The material has been classified as a clayey gravel with sand (GP) according to the Unified Soil <br />Classification System and that the grain size curve has been relatively consistent throughout all <br />rounds of refuse testing. The shear strength as measured by the direct shear apparatus has also been <br />very consistent such that no change in the original design shear strength has been required. These test <br />results are included in Appendix B. <br />2.2.2.2 Colluvium <br />Similar to the sampling procedure for the refuse material, bucket samples of colluvium were tested in <br />the laboratory. The colluvium tests included moisture content, Atterberg limits, standard Proctor, <br />fully -softened direct shear, residual direct shear, and consolidated -undrained triaxial shear. <br />The fully -softened shear strength is a peak drained shear strength envelope that simulates the <br />swelling and softening of a medium -stiff or stiffer fissured clay. While the degree of fissuring in the <br />colluvium is not well understood, it can be classified as a medium -stiff to stiff clay in which fissuring <br />could occur. For this reason, the fully -softened strength of the colluvium was tested using a direct <br />shear apparatus. The resulting fully -softened shear strength envelope from the six -point test was 24.9 <br />degrees with an apparent cohesion of 330 psf. <br />At sites where previous failures have occurred, the residual shear strength of the soils is mobilized <br />along the failure surface. To account for the possibility that the colluvium could mobilize its residual <br />shear strength, a correlation between liquid limit, clay -size fraction, and secant residual friction angle <br />proposed by Stark and Eid (1992) was utilized. The highest liquid limit measured in the colluvium <br />was 49 percent with a clay -size fraction in the 25 percent to 45 percent range. This leads to a residual <br />shear strength envelope of 22.0 degrees and zero cohesion. This strength envelope was used in the <br />analysis. <br />2.2.3 Modeling Methodology <br />The overall RPEE waste rock pile slope of approximately 3.2H:1 V (measured from the toe of the <br />waste rock pile at the buttress to the north edge of the top of the final waste rock pile top) includes <br />drainage and roadway benches and slopes of 2.0 H:1 V to 2.5H:1 V between the benches. The design <br />includes a buttress with a key trench, a rock underdrain along the thalweg of No Name Gulch, and a <br />0 <br />P:\Mpls\06 CO\26\06261003 MCC Refuse Pile Site Review & Permit\WorkFiles\Permit Application\2014 Revision\Exhibit 82 2014-05- <br />29.docx <br />