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Cripple Creek & Victor Gold Mining Company July 21, 2005 Timm C. Comer -4- 053-2399 placement in an angle of repose overburden facility and are not meaningful in evaluation of stability for the overall facility. Earthquake loads were simulated using apseudo-static approach. The pseudo-static approach was used because accelerations produced by seismic events rapidly reverse motion and generally tend to build to a peak acceleration that quickly decays to lesser accelerations. Consequently, the duration that a mass is actually subjected to peak seismic acceleration is finite, rather than infinite. The pseudo-static approach conservatively models seismic events as constant acceleration and direction, i.e., an infinitely long pulse. When using the pseudo-static approach, it is customary for geotechnical engineers to take only.a fraction of the predicted peak maximum acceleration. The pseudo-static coefficient for stability analysis for this evaluation was 0.14 g, which is consistent with the value presented in Amendment No. 8 to the Office of Mined Land Reclamation Permit M-1980-244 The results of the analyses (Appendix C) indicate the SGOSA has a minimum static factor of safety of 1.3 and a minimum pseudo-static factor of safety of 1.1. The results of the stability analyses corroborate the site observations and surface prism data, and indicate stable conditions. Deformation Analysis A deformation analyses was conducted to evaluate whether the movements recorded by the surface prisms can be explained by self-weight settlement of the overburden. The deformation analysis was conducted using Plaxis Version 8.0 (Plaxis, 2005). Plaxis is atwo-dimensional, finite element program designed to model rock, soil, and structure systems. The deformation model was constructed using the same critical section as [hat used For the stability analyses. In order to model self-weight settlement, the model was constructed using a phased construction approach, whereby overburden is placed as a series of lifts and allowed to settle with each subsequent lift. The deformation model included overburden and bedrock. The subgrade was not included as its contribution to settlement is considered very smaII given its limited thickness. The overburden and bedrock were modeled as Mohr-Coulomb materials. A summary of the material properties used in the deformation model is presented in Table 2. The bedrock was given a very high constant stiffness to represent the "floor" of the model. The bedrock stiffness was selected based on typical values presented in Bowles (1982). The overburden was given astress-dependent stiffness to simulate compression of the overburden with load. The stress-dependent stiffness was back-calculated from the prism data. The output from the deformation model is presented in Appendix D. The output from the model shows that predicted settlement of the overburden has vertical and horizontal components that closely resemble the observed deformations of the facility. Figure 5 presents a plot of measured and predicted vertical settlements at the crest of the SGOSA facility. The plot shows that the model closely simulates the measured vertical settlements. The results from the deformation model indicate that self-weightsettlement of the overburden explains the surface cracking observed along the crest of the SGOSA facility. 1:\OS2399~ptW\SGOSA SUbEvilOT10SO5R]99.Oa00Rep doc Golder AssoClates