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.+~~ ubjea Cresson Project ade by gFM ob xo 043-2251 <br />~ ~~1 r odified VLF Boundary hecked by JFl, ate 7/29/04 <br />~~~ Stability Analyses pprovedbyJFL bcetxo <br />1 of 5 <br />Evaluate the static stability of the Cresson heap leach pad in the vicinity of the modified VLF boundary. <br />METHOD: <br />Conventional limit equilibrium slope stability analysis using Rocscience's Slide version 5.0 computer <br />program (Rocscience, 2003). Static and dynamic loading conditions were analyzed using Spencer's limiting <br />equilibrium stability model. <br />ASSUMPTIONS: <br />Geometry /Water Surface: <br />' • The location of the cross-section used for the stability analyses is presented in Figure 1 (Attachment <br />1). This section intersects approximately the middle of the modified VLF boundary and the Phase II <br />VLF. <br />' • The ore heap is placed at an overall maximum slope of 1.6H:1V. The ore slope was continued for <br />the entire design section, which allowed for a maximum ore height of approximately 590 feet. <br />• Figure 2 (Attachment 1) illustrates the geometry of the study section. The liner systems (soil liner <br />t fill and geomembrane) were modeled as a si,igle layer with a thickness of 1 foot. The subgrade was <br />modeled as structural fill. <br />• The ore heap is placed at an overall maximum slope of 1.6H:1 V. The ore slope was continued for <br />' the entire design section, which allowed for a maximum ore height of approximately 590 feet. <br />• The piezometric head was modeled as 1 foot above and parallel to the lined surface, which is <br />consistent with the conditions used in Amendment No. 8 (CC&V 2000). <br />Material Properties: <br />The following material properties were used for the stability analyses, consistent with those used in <br />Amendment No. 8 (CC&V 2000): <br />TABLE 1-Material Strength Properties <br />Material Unit Weight, yW Effective <br />Cohesion, c' Effective Friction <br />An le, ' <br />Phase II LLDPFJSLF Inter ace 120 cf 1,590 sf 15° <br />Phase II/III LLDPF/SLFInte 120 cf 0 sf 18° <br />Ore 110 cf 0 sf 40° <br />Sub ade Structural Fil! 120 cf 0 sf 40° <br />Pseudostatic Loading: <br />For limit equilibrium analyses, seismic accelerations were conservatively evaluated by a pseudo- <br />static force of constant acceleration and direction, i.e. as an infinite long pulse. <br />Phacen-iIIFXT-Ctahility dnr, <br />