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Material <br />Peak Friction Angle <br />(Degrees) <br />Dry Density <br />(PCF <br />Moisture Content ( %) <br />Before <br />After <br />Stockpile at 6% <br />Moisture and Low <br />Density <br />39 <br />105 _ <br />5.7 <br />7.9 <br />105 <br />5.7 <br />15.7 <br />105 <br />5.7 <br />14.5 <br />Stockpile at 95% max. <br />Proctor Density and <br />Optimum Moisture <br />43 <br />113 <br />12.1 <br />- <br />113 <br />12.5 <br />14.9 <br />113 <br />12.5 <br />14.6 <br />Tailings (No <br />Compaction) <br />P ) <br />52 <br />64 <br />1.6 <br />28.9 <br />64 <br />1.6 <br />26.7 <br />64 <br />1.6 <br />25.8 <br />Tailings (Slightly <br />Tamped) <br />50 <br />67 <br />1.8 <br />31.3 <br />67 <br />1.8 <br />28.6 <br />67 . <br />1.8 <br />27.6 <br />percent of the maximum determined by our Proctor density on this material. We <br />replaced the fraction of gravel larger than 3/8 -inch in the stockpile sample tested <br />with sand so that tests could be performed using our equipment (nominal 3 -inch <br />diameter shear ring). The gradation for the stockpile sample is shown on Fig. A -3 <br />and the modified sample on Fig. A-5. The low density stockpile sample had a peak <br />friction angle of 39 degrees and the material remolded at 95 percent Proctor density <br />and optimum moisture had a peak friction angle of 43 degrees. The tailings <br />materials yielded peak friction angles of 50 and 52 degrees. These results are higher <br />than values from Vick for similar materials. According to the cited literature, gold <br />slimes have drained friction angles of 28 to 40.5 degrees. Vick also indicates friction <br />angles for clayey gravelly sand as 31 degrees. We considered these lower friction <br />angles in our slope stability analysis. <br />SLOPE STABILITY <br />THE UNION MILLING COMPANY <br />TAILINGS POND EMBANKMENT AND FUTURE TAILINGS SLOPE <br />UNION MILL <br />CTL T PROJECT NO. DN45,584 -130 <br />S:IPROJECTS4155001DN45584 .000113013. Letters1L11DN45584- 130- L1.doc <br />TABLE A <br />DIRECT SHEAR TEST RESULTS <br />We analyzed the stability of two sections of the proposed tailing pond <br />embankment and proposed tailings configuration shown on Fig. 2. The profiles were <br />based on drawings provided by The Union Milling Company dated May 13, 2011. The <br />stability of the slopes was evaluated for the following conditions: a) embankment, b) <br />embankment with tailings and water in- filled to the crest, c) embankment with <br />tailings mounded 20 feet above the crest with water. We estimated shear strength <br />parameters from the literature, results of laboratory strength tests, and our <br />experience. Shear strength parameters and unit weights used in our analysis are <br />summarized in Table B. <br />7 <br />