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1986), the strength parameters used for the compacted liner soils are reasonable and <br /> conservative. We have assumed the liner soils will be compacted to at least 95 percent of <br /> Standard Proctor density at or near optimum moisture content. <br /> Our stability analysis involved modeling the slope liner configuration and evaluating the factor <br /> of safety and failure surface orientation. Shallow surfaces (infinite slope or"raveling failures") <br /> were excluded from the analysis, as they should not impact the overall performance of the slope <br /> liner. <br /> The data provided suggest, the soil conditions are generally uniform across the site. For our <br /> analysis, the model incorporated one typical soil profile. This profile consisted of a 5-foot thick <br /> layer of clayey overburden soils, underlain by a 26-foot thick layer of sand and gravel. A 2-foot <br /> thick weathered bedrock layer was incorporated into the model 31 feet below the ground surface. <br /> Then firm bedrock was modeled below a depth of 33 feet. <br /> A 3:1 (horizontal to vertical) slope was initially analyzed. The slope geometry and configuration <br /> are shown in the Drawing section of this Project Manual. <br /> Four cases were analyzed for the slope configuration: an as-constructed or before water storage <br /> case, a rapid drawdown case, a full reservoir case, and a full reservoir with earthquake loading. <br /> For the rapid drawdown case, the shell was not considered free draining, but a thin layer of slope <br /> protection material was considered to be free draining. Therefore, for this case phreatic surface <br /> was raised to just below this free draining material. A pseudo-static horizontal acceleration <br /> coefficient of 0.1 g was used to determine earthquake loading for the full reservoir with <br /> earthquake case. <br /> Table 2 summarizes the results of our stability analysis. Output graphics for each of the analyses <br /> are provided in Attachment A of this Project Manual. The factors of safety required by the State <br /> Engineers Office (SEO) for these same loading conditions on above-grade embankment dams are <br /> listed for comparison. Considering that the consequences of failure are less for a below-grade <br /> slope liner than for a dam, lower factors of safety may be acceptable. However, the factors of <br /> safety for the 3:1 slope met or exceeded the SEO criteria for each case. <br /> Table 2: Deep Seated Failure Analysis Results <br /> Model As-Constructed Case Rapid Drawdown Full Reservoir Full Reservoir with <br /> Geometry and Earthquake <br /> Mode of Model SEO Dam Model SEO Dam Model SEO Dam Model SEO Dam <br /> Failure Factor of Factor of Factor Factor of Factor Factor of Factor Factor of <br /> Sae Sae o Sae Sae o Sae Sae o Safety Safety <br /> 3:1 (h:v) 2.1 1.5 1.3 1.2 2.4 1.5 1.4 1.0 <br /> SUMMARY AND RECOMMENDATIONS <br /> The stability models predict suitable factors of safety for 3:1 (horizontal to vertical) liner <br /> geometries. A toe berm may be locally required for site specific conditions where thick mud <br /> - 3 - <br />