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<br />~, <br />San Luis Mine - Phsse•n, Raise 1 Design Rcport <br />' tailings level rises to its maximum. Figures 4.1 and 4.2 depict the embankment geometry used for <br />upstream and downstream slope stability evaluations, respectively. <br />' Stability was analyzed using limiting equilibrium principles and atwo-dimensional idealized cross- <br />section of the embankment, tailings, and foundation. The stability analyses were conducted through <br />the use of the computer program PC STABL SM developed at Purdue University in West Lafayette, <br />Indiana. Rotational or circulaz failure surfaces utilized the Modified Bishop method for satisfying <br />moment equilibrium. Block or sliding wedge failure surfaces utilized the simplified Janbu method <br />for satisfying force equilibrium and utilized Janbu's empirical coefficient. Active and passive <br />portions of the wedge surface were determined according to Rankine Theory. <br />The STABL program incorporates a seazch routine to locate those failure surfaces with the least <br />factor of safety within user defined search limits and can analyze up to 1000 individual failure <br />surfaces in a single run. Successive program runs aze made to determine the mmst cridcal potential <br />failure surface. Computer printouts of the stability analyses are contained in Appendix D. <br />Stability analyses of the downstream face considered only failure surfaces which involved the entire <br />crest of the dam raise thereby having the potential to result in a release of tailings if they were to <br />' occur. Potential downstream failure surfaces involving less of the raise crest which may be slightly <br />less stable would not compromise physical containment of the solid or liquid components of the <br />' tailings. <br />Stability analyses of the upstream face of the embankment raise considered potential failure surfaces <br />' which involved the full height of the raise. As the analyses considered the critical condition for this <br />portion of the raise whereby no tailings are impounded by the raise, a failure corresponding to the <br />conditions analyzed would not compromise containment of the tailings. If a failure of the upstream <br />face occurs, there would be an opportunity to re-construct the failed portion prior to it being <br />required to contain tailings. As the tailings level in the impoundment rises, stability of the upstream <br />' face will increase. <br />' The following sections present the results of the stability analyses conducted under static and <br />dynamic loading conditions. <br />' 4.4 Static Loading Conditions <br />' Through repetitive analyses, the lowest factor of safety under static loading fot spy failure surface <br />considered was found to be 1.58 indicating that stability of the structure is within normally <br />' July 13, 1993 7 SRK Pmjecx No. 7M1719 <br />1 <br />