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<br />San Luu Mine - Ptuueln, Roue 1 Design Report <br />' motions. Selecting a specific failure surface it is then possible to determine the average earthquake <br />induced acceleration and yield acceleration (i.e. the acceleration which resulu in a factor of safety <br />of unity). The displacements which occur any time the induced acceleration exceeds the yield <br />acceleration is then evaluated by simple numerical integration. <br />Makdisi and Seed calculated the deformation induced in a variety of embankments, ranging in height <br />from 75 to !50 ft with varying slopes and material properties, which were subjected to accelerations <br />' from three different magnitude earthquakes (6'h, 7'fi, and 8'/a) scaled to peak ground accelerations <br />ranging from 0.2 to 0.75g. They analyzed a variety of failure surfaces with a wide range of yield <br />accelerations and present an envelope of the resulting displacements for each magnitude earthquake <br />' relative to the ratio of the yield acceleration to the average maximum acceleration induced on the <br />slide mass. <br /> <br /> <br />1 <br /> <br />1 <br /> <br /> <br /> <br /> <br /> <br /> <br />The Corps of Engineers and Makdisi and Seed methods have been utilized to estilttate displacements <br />for each dam section and failure surface previously analyzed for static stability. While these <br />methods give a numerical result, their approximate nature must be incorporated by assuming the <br />results indicate the order of magnitude for displacements rather than the actual value. The <br />displacement analyses incorporated three levels of earthquake ground motion, 0.2g, 0.4g and O.tig <br />(site MCE event as defined in the Permit and Amendment), and assumed no modification to the base <br />motion as a result of embankment response or liquefaction of tailings. <br />4.5.2.2 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 force 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 STA$L SM computer <br />program. <br />The lowest yield acceleration calculated for either embankment face was 19.8 percent of gravity <br />(0.198g). This yield acceleration was calculated for a sliding wedge type failure of the downstream <br />face with basal sliding along the embankment-liner interface. The lowest yield accelerations <br />computed for sliding wedge and rotational type failures of both embanlanent slapes aze given in <br />Figures 4.1 and 4.2. <br />July l3, 1993 lp SRK Project No. 14719 <br /> <br />