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emergency spillway elevation, az well az, with the pond drained quickly (rapid drawdown condition). In • <br />addition, the analyses were run with and without a horizontal seismic coefficient. <br />Based on the results of the stability analyses for the Small Dam's Drainage System, which are <br />summarized in Appendix B, the lowest factor of safety obtained waz for the rapid drawdown condition. <br />The factor of safety obtained for this scenario was 2.03. The factor of safety for the slope stability <br />failure with and without horizontal seismic coefficient of O.OSg were 2.18 and 2.54, respectively. The <br />stability analysis results for the Mirafi Blanket System are very similar and are shown in Appendix C. <br />EMBANKMENT DETAIIS <br />Foundation: The foundation and embankments were designed on the principal of a pervious <br />foundation which allows some seepage below the embankment into the proposed drain system. The <br />embankments will be placed on the overburden soils az described in the subsoils section. The <br />embankments will consist of pervious foundation earth dam with a key trench excavated into the <br />underlying overburden soils and a horizontal drainage system. The subsoils encountered are suitable <br />for support of the structure. A negligible amount of settlement can be anticipated for the overburden <br />soils. Some minor settlement of the embankment materials should be anticipated. <br />Comaaction: We recommended that the embankment and key trench materials be compacted to at • <br />leazt 95% of the maximum standard Proctor density within 3% of the optimum moisture content, az <br />determined by ASTM D698. In order [o meet the moisture content specifications, the contractor <br />should anticipate adding water to the embankment materials prior [o compaction. The till should be <br />placed under controlled conditions and observed and tested by a soils engineer. The fill lifts should not <br />exceed 8 inches in thickness. Fills should be benched into hillsides exceeding 4 (horizontal) to 1 <br />(vertical) slopes. The fill materials placed in the embankment should consist of the clays, sandy clays <br />and clayslone bedrock encountered in the borrow areaz. The materials should be free of topsoil, <br />vegetation, brush and other deleterious substances and should no[ contain rocks or lumps greater than <br />4 inches in diameter. All topsoil should be removed prior to fill placement. <br />Overbuild: The embankment foundation soils will undergo a negligible amount of settlement. The <br />embankment materials will consolidate with lime and based on our experience, we estimate lltat the <br />settlement will be on the order of 6 to 12 inches. We recommend that the embankment section be over <br />constructed with approximately 1 foot oC additional material in the central portion of the dams. <br />C~ <br />J <br />lob No. 91-562 Ground [ngineering Consullan~s, Inc. Page 6 <br />