2008-04-15_REVISION - M1980244 (256)

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,~ SMITH WILLIAMS CONSULTANTS, INC. • 5.2 Settlement 5.2.1 PSSA Foundation Settlement calculations were completed for both the Phase 5 VLF PSSA side-slope (the regraded Phase IV ore slope), and the PSSA embankment. Settlement analyses were conducted using the numerical model Plaxis V8.2 (Plaxis 2007). Plaxis is atwo-dimensional, finite element program that is used to analyze the response of geomaterials under applied loads. The results of the settlement calculations are presented in Appendix C. For the PSSA embankment, settlement was calculated by "constructing" the embankment within the model and.applying the maximum ore loading from the VLF. The embankment materials were modeled as afine-grained rock fill with a unit weight of 120 pcf, with an effective friction angle of 32 degrees and zero cohesion. The embankment materials were modeled as a linear elastic soil, with a modulus of 5,800 psi, which is based laboratory test data. The results of the settlement calculations are presented in Appendix C and indicate that the anticipated settlements along the PSSA embankment will likely be less than 1 inch under the applied ore loading. These settlements are considered minor and are not anticipated to damage the PSSA liner system. For the Phase 5 PSSA side-slope, which is to be constructed along the existing Phase IV ore slope, a model. section was constructed based on the existing site conditions and the proposed grading plan. The model focused on the deformation of the regraded ore slope (PSSA side- slope) as the ore height in the VLF increased to 590 feet. For this model, the ore on the liner was modeled as astrain-hardening material, whereby the stiffness increases with applied stress. The ore shear strength was modeled with a friction angle of 40 degrees, with zero cohesion. The unit weight of the ore was set to 118 pcf, which equivalent to the ore at field capacity moisture content. The strain-hardening model used in Plaxis takes the form of: Where Eief is the initial (reference) elastic modulus, which was set at 130,000 psf. The reference pressure (pLef) was set at 100 psf, and the power constant (m) was set to 0.32. The strain- hardening parameters were derived by calibrating actual ore compressibility from lab tests to the strain-hardening model. The modulus .values presented agree well with typical values for fine- grained rockfill as presented in Hunter and Fell (2003) and Bowles (1982). S:\PROJECTS\1125 CCBV PHASE 5 VLF\H2 - DESIGNWREQUA VLF\VLF PHASE 5 FINAL REPORT V2.DOC 3