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<br />San Luis Mine Phase II, Raise 2 Design Report <br />' referred to as apost-earthquake stability analysis and is advocated by numerous authorities on <br />earthquake stability of dams and embankments (Finn, 1982; Seed, 1987; Lo and Klohn, 1990; <br />Marcuson, Hynes and Franklin, 1990; and Ishihara, 1993). <br />' With this type of analysis, the structure's stability is evaluated for static loading conditions with <br />' post-liquefaction residual strengths to determine if the driving forces exceed the resisting forces. <br />If this is not the case, a flow slide can not occur and the structure is determined to be stable. Phis <br />method assumes that the dam or embankment will be safely able to tolerate the limited deformations <br />' which occur during the earthquake shaking. For the San Luis tailings facility the post-earthquake <br />stability analysis method predicts a large factor of safety against a flow slide as indicated by the <br />' relatively large yield accelerations, i.e. inertia forces, which are required to reduce the factor of <br />safety to 1.0 for post-liquefaction conditions. <br />' It should also be clearly understood that the probability of the MCE event occurring is very low. <br />Based on Dr. Glass' estimates of probability presented in the Permit, there is a 0.1 to 2.5 percent <br />' probability that 0.6g PGA could be experienced at the site in the next 20 years. <br />Construction of the dam raise will include establishing survey control points along the crest of the <br />' raise and existing embartlnttent as well as various locations on the downstream face. Following any <br />large earthquakes in the area, these survey points can be utilized to determine if any deformation <br />_ of the structure has occurred. This will provide a basis for determining the extent, if any, of <br />' damage to the structure, and although unlikely, the need for remedial action. 'litre dam should also <br />be inspected by a qualified geotechnical engineer for any signs of cracking, increased seepage, and <br />' slope instability or bulging. <br />' Long term stability of the structure will increase as time goes by as the tailings consolidate. <br />1 <br />1 <br />1 <br /> <br /> <br />~ Y 5.2 ro~ect o. <br /> <br />