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• ~ ~ <br />L ~ J~ <br />Moisture Content <br />Moisture contents of the coarse and fine mix ranged from 15.2 to 22.5 percent <br />with an average of 19.1 percent. The Proctor optimum moisture was 12.5 percent. <br />We recommended -5 to +3 percent of Proctor optimum moisture as a process goal. <br />Our experience is that slightly higher moisture contents are acceptable provided the <br />required compaction is achieved. The material was sampled soon after processing. <br />During RDA construction the transportation, piling and spreading operations will <br />result in drying during portions of the year. We believe the moisture contents <br />measured are suitable for placement in the RDA provided drying is accomplished <br />during placement and that compaction can be achieved. Laboratory compaction data <br />and our experience suggests compaction will be difficult at moisture contents more <br />than 5 percent over optimum (over 17.5 percent). In addition, during wet times of the <br />year, the wetter process materials could be more susceptable to developing <br />saturated layers and free water in the fill. <br />We do not recommend a moisture content specification. Our experience <br />indicates compaction will be more difficult at higher moistures, but if achieved the <br />stability assumptions in our design will be met. <br />Direct Shear <br />We pertormed a direct shear test on a remolded sample compacted to a <br />density equivalent to 90 percent of the maximum standard Proctor dry density (ASTM <br />D 698) near optimum moisture content. The material larger than the #4 sieve was <br />replaced with + 3/8 to - #4 sized material to create a test specimen with a similar <br />proportion of fines. The test results indicated a friction angle of 42 degrees (Fig. 3) <br />which is well above the minimum assumed in the design (30 degrees, no cohesion). <br />Summary <br />The results of the laboratory testing indicate the processed material <br />possesses equal or better engineering properties than assumed in the design. The <br />comparatively high moisture content of the waste may lead to compaction difficulties <br />or to development of free water and saturated lenses in the fill. We recommend <br />monitoring of the compaction during initial placement, and inspection of the material, <br />to evaluate these concerns. <br />Limitations <br />Our recommendations were developed in a manner consistent with the level <br />of care and skill ordinarily used by geotechnical engineers practicing in this area at <br />TWENTYMILE COAL COMPANY <br />CM 22,257 <br />2 <br />