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<br />33 <br />Geotechnical Design of Fill Areas (Exhibit #13) <br />CTL/I'hompson, Inc., geotechnical consultant to the applicant, presents a preliminary <br />generalized stability analysis of the proposed head of hollow fills within Exhibit #13. <br />This analysis was performed to determine the theoretical slope stability of two fill cross <br />sections. CTL/I'hompson, for purposes of this generalized analysis, has divided the 21 <br />proposed fills into two populations. The two chosen theoretical cross sections analyzed <br />aze portrayed as representing these two fill types, characterized as the "low section" and <br />°high section" fills. The hypothetical cross sections appear to be representative of the <br />proposed population of Fills. <br />In completing the analysis, CTL/Thompson, Inc. has varied the parameters of the analysis, <br />including material strength (angle of internal friction and cohesion), and the degree of <br />moisture. In completing the earthquake impact analysis (pseudo-static slope stability), <br />CTL/T'hompson applied three different acceleration factors. This style of pazametric <br />analysis, is commonly referred to as a "sensitivity analysis". Variation of the applicable <br />parameters allows the determination of the sensitivity of the result (factor of safety) to <br />each of the parameters. In this manner, potentially critical parameters may be defined. <br />The technician may determine the possible consequences of variation or error in <br />parameters such as the material strength or degree of saturation of the fill. Sensitivity <br />(parametric) analysis has proven to be a valuable tool in analyzing the relative stability <br />of earthen structures. <br />Analytical Assumptions <br />In completing the preliminary analysis CTL/Thompson, Inc. was required, of necessity, <br />to complete numerous assumptions: <br />(1}"The fill heights range from about 50 feet to 250 feet (toe to crest) with the maximum <br />thickness of till below the crest ranging from about 50 to 170 feet." <br />(2)"We estimated the average valley slope and maximum side slopes to compare to the <br />CDMG definition of Valley Fills." <br />(3)Conditions at the spoil disposal sites regazding geology, topography, soils, and ground <br />water were generalized. <br />(4)Fill foot print azeas were considered to be free of seeps. <br />(5)The fill foundation azeas were assumed to be stable. <br />(6)"Previous testing of a bulk sample of colluvial{residual clay soil from the New Elk <br />RDA Site indicated a liquid limit of 37 percent, plasticity index of 16 percent, and 63% <br />silt and clay sized particles. This low plasticity, sandy clay is considered consistent with <br />