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0 / I YieldAcceleration <br />The second step in the seismic slope stability analysis was to determine the yield <br />acceleration for cross-sections AA, BB, and CC using a pseudo -static slope stability <br />analysis. The yield acceleration is the magnitude of horizontal acceleration that reduces <br />the factor of safety to unity (i.e., 1). Iterative analyses were performed to determine the <br />yield acceleration value for each of the three global slope stability cross-sections. <br />In the pseudo -static analysis, it was assumed that the base liner and the sideslope liner <br />systems will meet a minimum residual shear strength envelope defined by a friction angle <br />of 10.5 degrees, based on the static analysis discussed previously. Also, in cross-section <br />AA, the waste sideslope was assumed to be 3H: I V. In cross-sections BB and CC, the <br />waste sideslope was assumed to be 3.5H:1V. In addition, 20 -foot benches were assumed <br />at elevations 300, 350, and 400 feet within all three cross-sections, as noted under the <br />static analysis. <br />The results of the pseudo -static slope stability analyses are presented in Attachment 3. <br />The yield acceleration was determined to be 0.09g for all three cross-sections. Since this <br />values is significantly higher than the kmax value of 0.054, the potential for permanent <br />displacement during the MPE does not exist. Because of this, a site response analysis <br />using SHAKE computer program is not warranted, and therefore, not performed. Also, <br />since no permanent displacement is anticipated, a Newmark analysis was not required. <br />4.5 Conclusions From the Seismic Slope Stability Analyses <br />The seismic slope stability analyses results discussed above shows that as long as the <br />Module l liner systems satisfy the residual shear strength envelope defined by a friction <br />angle of 10.5 degrees and the waste slope geometry restrictions discussed under the static <br />analyses, permanent displacement would not take place during the MPE. <br />Liquefaction of the foundation soil at the FSL site is not a concern for the following <br />reasons: <br />• As noted earlier in the report, the groundwater table at the FSL site is located at <br />depths greater than 150 feet below the existing ground surface. <br />• The foundation soils consist of non -liquefiable, hard, cemented sandy silt and <br />clay. <br />• The site is located in a low seismicity area. <br />N:\sacDP12002\PRJ\PJ8\83\835608.2bz.doc EMCOWOWT, Inc. <br />Rev. 0, 07/31/02 <br />4-3 <br />