2008-04-15_REVISION - M1980244 (256)

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~; "~ SMITH WILLIAMS CONSULTANTS, INC. The results of the PSSA side-slope settlement analysis indicate that the PSSA slope will settle approximately 5 feet under the applied ore load. Based on these results, the PSSA bench on the Phase IV ore slope will be completed at an elevation of 9,775 feet to accommodate long-term settlement. The PSSA liner strain is predicted to be less than 5 percent, which is acceptable for LLDPE geomembrane liner. 5.2,2 VLF Foundation Settlement calculations for the VLF foundation considered two conditions: 1) settlement of the VLF foundation under the application of 800 feet of ore, and 2) settlement of the regraded AGOSA slopes under the application of 590 feet of ore. Settlement of the VLF foundation was analyzed using the Plaxis V8.2, finite-element code. The results of the settlement calculations .are presented in Appendix C. For the VLF foundation under 800 feet of ore, a model section was created through the Phase I VLF, where the ore loads are anticipated to be the greatest. This section also crossed the Phase UPhase IV and the Phase IV/Phase 5 boundaries, where extensions of the liner system were made in previous Amendments. These locations were selected to assess the strain in the geomembrane • within the extension areas: For this analysis, the model focused on the deformation of the structural fill beneath the geomembrane liner system. The structural fill was modeled as a linear elastic soil with an effective friction angle of 32 degrees and zero cohesion. The soil modulus was set at 5,800 psi, which was based on laboratory test results. The results from the settlement analysis indicate that the VLF foundation is anticipated to settle less than 2 feet under the maximum ore load. This displacement occurs at the mid-slope of the. PSSA, not at the crest. Maximum strains along the geomembrane liner are predicted to be less than 5 percent, which is acceptable for LLDPE geomembrane liners. For the settlement of the AGOSA foundation, a model section was developed along the AGOSA slope, which also crosses the relocated Carlton Mill tailings. In the model, the AGOSA material was modeled as a coarse rock fill. The rock fill properties (unit weight and stiffness) were derived from a previous settlement analysis of Squaw Gulch Overburden Storage Area (SGOSA) facility. The rock fill was modeled as astrain-hardening material with a stiffness that varies with applied normal stress. The strain-hardening model used in Plaxis takes the form of: Where Eief is the initial (reference) elastic modulus, which was set at 823,700 psf. The reference pressure (P`ef) was set at 100 psf, -and the power constant (m) was set to 0.50. The strain- S:\PROJECTS\1125 CCBV PHASE 5 VLF1H2 - DESIGNWREQUA VLF\VLF PHASE 5 FINAL REPORT V2.DOC ~~