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f j <br />0?1 <br />SMITH WILLIAMS CONSULTANTS, INC. <br />Project: CC&V Phase 5 VLF Job No. 1125 <br />Calculation Title: <br />Phase Iv a Ore Slope Settlement <br />Prepared B : JFL Date: February 29 2008 <br />Checked B : DTW Date: March 14 2008 <br />OBJECTIVE: <br />Assess the settlement and potential strain of geomembrane along the Phase IVa ore slope as the <br />Phase 5 VLF is loaded to 10,320 ft elevation (590 ft). These analysis will be used to estimate the <br />settlement along the PSSA bench (9770 bench on the Phase IVa slope), to assess strain in the Phase <br />5 PSSA liner system, and to assess strain on potential pipelines to be located along the 9770 bench. <br />METHOD: <br />Use PLAXIS, a two-dimensional finite element program to assess stress and strains under the 590 ft <br />ore height. <br />Apply the model to a cross-section that cuts through the Phase IVa ore slope, where the ore height <br />reaches 590 feet (see Figure 1). <br />ASSUMPTIONS: <br />• Since the focus of the analysis is the strain and deformation of the ore slope, bedrock was <br />"modeled" just below the Phase IVa and Phase 5 liner systems (e.g. the structural fill <br />beneath between the liner system and bedrock is ignored). <br />• Given the scale of the model, the geomembrane liner on the Phase IVa ore slope cannot be <br />modeled explicitly; however the liner strains can be estimated using the strains along the ore <br />surface of interest (e.g. the geomembrane liner does not contribute to the strength). <br />• The ore on the liner was modeled as a strain-hardening material with a friction angle of 40 <br />degrees, with zero cohesion. The unit weight of the ore was set to 118 pcf, which equivalent <br />to the ore at field capacity moisture content. The strain-hardening model used in Plaxis takes <br />the form of- <br />E = E-f (cr / P•ef )m <br />Where E'f is the initial (reference) elastic modulus, which was set at 130,000 psf. The <br />reference pressure (P-f) was set at 100 psf, and the power constant (m) was set to 0.32. The <br />strain-hardening parameters were derived by calibrating actual ore compressibility (from lab <br />tests) to the strain-hardening model. The curve fit between the lab data and the Plaxis model <br />are shown below. The modulus values presented agree well with typical values for fine- <br />grained rockfill as presented in Hunter and Fell (2003) and Bowles (1982). <br />C7