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<br />. <br /> <br />Conclusions <br /> <br />1) The subsurface conditions encountered across the project site were variable, The subsurface conditions <br />encountered in the test holes advanced in the upstream face of the dam embankment typically consisted of <br />16 to 28 feet of clay fill materials overlying a layer of natural topsoil materials, which in turn were <br />underlain by natural clays and claystone bedrock to the maximum depth investigated, 41 feet The <br />subsurface conditions encountered in the test holes and test pits advanced in the proposed borrow areas <br />were fairly consistent and generally consisted of a thin layer of topsoil overlying natural clays, sands and <br />ciays, and claystone bedrock to the maximum depth investigated, 25 feet, <br /> <br />2) <br /> <br />Based on the results of the field and laboratory investigations, our conversations with the client and our <br />experience with similar projects, it appears that the failure on the upstream face of the dam embankment <br />was a result of a number of conditions at the site, such as the construction of the original embankment over <br />the natural topsoil materials, the steepness of the existing embankment slope prior to the failure, the fairly <br />rapid and historic draw down of the water levels in the reservoir and the repairs/modifications previously <br />completed at the site by the client in the failed area, <br /> <br />. <br /> <br />3) Based on the subsurface conditions encountered along the upstream face of the embankment and in the <br />proposed borrow areas, we believe that the most economical and feasible method for rehabilitating the <br />embankment will be to remove all of the failed materials and then construct a new embankment section <br />along the upstream face of the existing embankment The new embankment fill materials should be placed <br />and compacted to at least 95% of the maximum standard Proctor density and within 3 percent of the <br />optimum moisture content determined in accordance with ASTM 0-698, The finished, compacted <br />embankment slope should be constructed to a 3,5 (horizontal) : I (vertical) or flatter configuration. The <br />new embankment section should be founded on the natural clays encountered below the natural topsoil <br />materials and a cutoff trenchlkeyway should be excavated into the underlying claystone bedrock materials. <br />The fill materials required for the construction of the keyway/cutoff trench and the reconstruction of the <br />upstream section of the embankment will be obtained from the proposed borrow areas situated to the <br />southeast and east of the existing reservoir. Based on the results of the field and laboratory investigation, it <br />appears that suitable quantities of relatively impervious clays should be available in these borrow areas, <br /> <br />. <br /> <br />4) <br /> <br />Due to the steepness of the downstream face of the existing embankment, we recommend that the suitable <br />soils being removed/excavated from the upstream face of the embankment in the failed area be placed and <br />compacted along the downstream face of the embankment The compacted fill materials should be <br />properly keyed/benched into the existing embankment materials after the topsoil materials and vegetation <br />have been removed, The finished, compacted embankment slope should be constructed to a 2.5 <br />(horizontal) : I (vertical) or flatter configuration, <br /> <br />5) Based on the condition of the existing outlet pipe and intake structure, and the proposed embankment <br />reconstruction and modifications, a new outlet pipe and intake structure will be constructed in the natural <br />abutment situated between the existing embankment and spillway, The existing outlet pipe will be <br />abandoned and filled with concrete prior to the placement of the new embankment fill materials, <br /> <br />. <br /> <br />Job Number. 00-4660 <br /> <br />NWCC, Ine, <br /> <br />Page 1 <br />