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ComRaction: We recommend that all of the embankment materials be uniformly placed and compacted ie 8 <br />inch lifts to at least 95% of the maximum s[andazd Proctor density and within Z percent of the optimum <br />moisture content as determined by ASTM D698. The fill should be placed under controlled conditions and <br />observed and tested by the soils engineer. All fill materials placed in the embankment should be free of topsoil, <br />organics and other deleterious substances, and should not contain rocks or lumps of soil greater than greater <br />than 6 inches is size. <br />Slone Protection: We recommend that the finished embankment slopes and other disturbed areas be protected <br />from erosion by revegetating them as soon as possible. Riprap armoring of the upstream face of the pond <br />embankment may be required [o protect [he embankment from the erosion effects of wave action within the <br />impoundment. <br />Overbuild: Both the natural subgrade soils and the compacted embankment materials will consolidate with <br />time, and based on our experience, we estimate [ha[ the overall settlement will be on the order of 6 to 12 inches. <br />We recommend that the embankment section be overconstructed with approximately 1 foot of additional <br />material in the cenval portion of [he dam. <br />STABILITY ANALYSES <br />• To analyze the stability of [he slopes is the proposed embankment and its interaction with [be tmderlying soils <br />and bedrock, we used a microcomputer program called SB-SLOPE. This program is a comprehensive slope <br />stability program for microcomputers using the "Simplified Bishop Method of Slices". <br />The soil strength values used for the natural soils were obtained from the triaxial shear strength tests conducted <br />on relatively undisturbed samples of the natural sands and clays. The soil svength values used for the <br />embankment materials were based oa the test results obtained on similar fill materials used at Pond 010 and <br />the unconfined compressive svength tests run on remolded samples obtained from the proposed borrow area. <br />Due to the hardness of the bedrock, we could not obtain samples of the sandstone for laboratory testing; <br />therefore, we have assumed a conservative strength value, based on our experience with similar materials in [his <br />azea. <br />Haled on the laboratory test results, a dry density of 118.0 pcf, a cohesive strength value of 450 psf and phi angle <br />of 15 degrees was used for the remolded embankment materials. For the natural, undisturbed overburden soils <br />an average dry density of 120.0 pcf, a cohesive strength value of 250 and phi angle of 7 degrees were determined <br />from the laboratory testing. Based on otv experieoce with similar materials a dry density of 125.0 pcf a cohesive <br />svength value of 2,500 psf and phi angle of 20 degrees were used for the sandstone bedrock. <br />Based on the results of the stability analysis, [he minimum Cac[or of safety under static loading was 1.:~4 for [he <br />embankment with the good full. Therefore, [he pond design as presented by the client should result in a factor <br />lob No. 97-7000 Nonhwrst Colorado Consultants, Inc. Page 5 <br />