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<br />' San Luis Mine Phase D, Raise 2 Design <br />' to evaluate embankment response. Makdisi and Seed calculated the deformation induced in a variety <br />of embankments, ranging in height from 75 to 150 ft with varying slopes and material properties, <br />which were subjected to accelerations from three different magnitude earthquakes (6'k, 7'fz, and <br />' 8'/a) scaled to peak ground accelerations ranging from 0.2 to 0.75g. They analyzed a variety of <br />failure surfaces with a wide range of yield accelerations and present an envelope of the resulting <br />' displacements for each magnitude earthquake relative to the ratio of the yield acceleration to the <br />average maximum acceleration induced on the slide mass. <br />' Ambraseys and Menu (1988) present an update of the earlier work of Franklin and Chang (1977) <br />and Makdisi and Seed (1977). They update these previous studies with recent strong motion records <br />paying particular attention to near-field ground motions in order to improve upon the correlation <br />between permanent displacement and earthquake characteristics for these events. The magnitude <br />range for which near-field data is available is limited and the study of these events was restricted <br />' to the magnitude range of Ms=6.9 +/- 0.3. Thus these results are directly applicable to the San <br />Luis facility MCE ground motions. Ambraseys and Menu present their results in graphical form <br />' with various levels of probability of exceeding a given displacement for each critical acceleration <br />ratio ("yield acceleration" divided by PGA, see Section 4.6.2.2). <br />' The Corps of Engineers, Makdisi and Seed, and Ambraseys and Menu methods have been utilized <br />to estimate displacements for each dam section and Failure surface previously analyzed for static <br />_ stability. While these methods give a numerical result, their approximate nature must be <br />' incorporated by assuming the results indicate the order of magnitude for displacements rather than <br />the actual value. The displacement analyses assumed no modification to the base motion as a result <br />' of embankment response or liquefaction of the tailings or phase relationships of the motion over the <br />height of the structure. Thus the average acceleration acting on the potential failure masses has been <br />' assumed to be 0.6g. <br />4.6.2.2 Yield Accelerations <br />' In order to estimate displacements on a failure surface due to seismic loading, it is necessary to <br />determine the "yield" acceleration for the potential failure surface. The yield acceleration is defined <br />' as the average acceleration acting on a mass above a potential sliding surface that results in a <br />horizontal inertia fotce which coupled with static forces results in a factor of safety of unity for <br />' sliding of the mass along the potential failure surface. The yield acceleration was calculated through <br />conventional limiting equilibrium stability analysis methods utilizing the PC STABL SM computer <br />program. <br />' The lowest yield acceleration calculated for either the upstream or downstream embankment face <br />' was 0.106g. This yield acceleration was calculated for a sliding wedge type failure of the <br />u Y 4-8 ro~ect o. <br />