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1 <br />t July 23,1998 mil- 983-2348.160 <br />STABII.ITY RESULTS <br />Golder calculated the FOS for each section based upon a general layout of 1.6H:1V <br />sideslopes and a maximum Ore depth of 320 feet. The maximum sideslope of 1.6H:1V was <br />' calculated based upon an infinite slope analysis, which determined the steepest sideslope <br />which will still provide a FOS of 1.0 for surface raveling of the ore material during a 0.148 <br />seismic event. Calculations are presented in Attachment A. Therefore, a sideslope of <br />1.6H:1V was selected as a maximum Ore sideslope for the valley leach pad. <br />' The slope stability of the valley leach facility was evaluated using five stability sections. <br />Sections A-A', B-B', C-C', and D-D', are as located previously in a January 21, 1997 <br />letter to CC&V, with cross-sections A-A', B-B' and C-C' located in Phase II perpendicular <br />to the valley drainage, and cross-section D-D' located in the Phase I/Phase I Expansion <br />area. Cross-section E-E' is transverse to the centerline of the Phase II Toe Berm, and was <br />located such that the potential effects on the valley leach stability of the underdrain corridor <br />' could be ascertained. Two possible failure modes were evaluated along section E-E': (1) a <br />failure along the geomembrane and Soil Liner that exits through the Cresson ore buttressed <br />by the Phase lI Toe Berm, and (2) a translational failure under the Phase II Toe Berm, <br />' along the underdrain. <br />A plan view identifying the section locations is shown in Figure 1, and cross-sections with <br />critical surfaces are shown in Figure 2. The slope stability output files aze presented in <br />Attachment B. <br />' TABLE 1 <br />' SUMMARY OF FOS VALUES <br /> <br />1 <br />1 <br /> <br />1 <br /> <br />1 I:\98\.398\1]48RR4.LTR <br />...:..:...:..::.:..: <br />.`: n :.::::.. <br />•: `::: ~ectto ..... .. <br />. <br />. <br />:::::..` fade::::::: <br />S ............. . <br />'::::::::::statie::F : .;;::.<;.;; <br />A <br />A; 2.2 1.5 <br />B-B' 2.l 1.2 <br />C-C' 1.5 1.1 <br />D-D' 2.5 1.8 <br />E-E'~ 1.6 1.1 <br />E-E'" l.5 1.0 <br />FOS of wedge failure upgradient of Phase Il Toe Berm with an ore sideslope of 2.SH:IV <br />•' FOS of translational failure along underdrain Through Phase 11 Toe Berm with an ore sideslope o(2.SH:1 V <br />Golder Associates <br />