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1 <br />SECTIONTHREE Stability Analyses <br />' • Existing height embankment under static undrained loading condition using the phreatic <br />' surface corresponding to 6 weeks after the PMP event. <br />• Ultimate height embankment under pest-seismic loading condition using the phreatic surface <br />corresponding to the normal operating pond conditions. <br />' • Ultimate height embankment under post-seismic loading condition using the phreatic surface <br />corresponding to 6 weeks after the PMP event. <br />• Ultimate height embankment under static undrained loading condition using the phreatic <br />surface corresponding to 6 weeks after the PMP event. <br />' • Post-closure ultimate height embankment using the phreatic surface cotrespondin.g to 10 <br />years after drawing down the PMP pool (PMP pond was assumed to be sustained for 6 <br />weeks, after which the entire decant pond was assumed to be drained). Both static undrained <br />' and post-seismic loading conditions were evaluated for the post-closure geometq•. <br />Seepage conditions in the embankment following the PMP event were evaluated usirl.g both the <br />' "base case" conductivities and 1 order of magnitude higher than the "base case" condluctivity for <br />the tailing sands material. A comparison between the two phreatic surfaces indicates that the <br />higher tailing sands conductivity yields a higher phreatic surface at the end of 6 weeks following <br />' the PMP event. To conservatively estimate the stability of the embankment following the PMP <br />event, the higher phreatic surfaces were used in the slope stability analyses. The "bare case" <br />conductivities were used to estimate the phreatic surface afer 10 years. This assumption is <br />' conservative because water pressures dissipate slower for the "base case" conditions. <br />3.4 RESULTS AND ASSUMPTIONS <br />' Presented below are the results of our stability analysis followed by a discussion of our <br />assumptions. <br />' Results <br />' The post-seismic minimum factors of safety range between 1.09 and 1.13 for the existing height <br />embankment, at the end of 6 weeks following the PMP event, as shown in Figure 7. For the <br />same geometry, under static undrained loading condition, the minimum factors of safety range <br />' between 2.06 and 2.12 as shown in Figure 8. <br />The minimum factors of safety range between 1.23 and 1.30 for the ultimate height embankment <br />under post-seismic loading condition, using the phreatic surface corresponding to the normal <br />' operating pond conditions, as shown in Figure 9. <br />Following the PMP event, for the ultimate height embankment, the minimum factors of safety <br />' range between 1.04 and 1.08, for the post-seismic condition, and between 1.95 and 2.07, for the <br />static undrained loading condition, as shown in Figures ]0 and 11, respectively. <br />For the post-closure ultimate height embankment, using the phreatic surface corresponding to 10 <br />' years afer drawing down the PMP pool, the minimum factor of safety is 1.05 for the post- <br />seismic condition and 1.90 for the static undrained loading condition, as shown in Fil;ures 12 and <br />13, respectively. <br />Y~7 N.\PROJECTSKBaa618_HENDERSON_MILL_BARG\SUB_OP6.0_PROJ_DELMHJdILL R3000\]4JUL-01\\ 3-2 <br />