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1 <br />San Luu Mine -Phase Q, Rsiac 1 Deign RcpoR <br />i' embankment raise and PGA=0.6g, the displacement estimated for both the failure surfaces depicted <br />on Figure 4.1 is approximately 2.1 feet. <br />~' <br />5.0 CONCLUSIONS AND RECOMMENDATIONS <br />The data collection and evaluations presented herein were conducted to confirm and finalize the <br />' conceptual designs for the embankment raise presented in the Amendment. Evaluation of the <br />tailings adjacent to the existing Phase I embankment confurmed the lack of significant amounts of <br />saturated, liquefiable tailings beneath the proposed upstream raise. Dynamic stalbility analyses based <br />' on a refined model of the structure confirmed that the conceptual raise design provides a stable <br />structure and no modifications to this design were necessary. <br />' Displacements on the order of magnitude estimated for the raised embankment under the levels of <br />earthquake ground motion considered do not pose a threat to the integrity of the structure. The <br />displacements calculated would not result in a loss of freeboard sufficient to allow escape of tailings <br />solids or liquid, therefore positive containment would be maintained. Following~the earthquake, the <br />deformed crest of the embankment could be re-constructed to provide sufficient freeboard for full <br />containment of PMF inflows if required. <br />' The primary concern with respect to deformations of the order estimated for 0.6g PGA is the <br />integrity of the liner system beneath the embankment. With 2.2 ft of displacemeAt for a wedge type <br />of failure involving sliding on the liner, there is a possibility that the geomemblane component of <br />' the liner system could be torn. However, as presented in the Amendment adlequacy responses, <br />several key factors reduce this possibility and the consequences should it occur. <br />' In the event the geomembtane liner is torn, the underlying soil component of the liner system would <br />serve to limit the loss of contained fluids. Although the displacement analyses assume that failure <br />' occurs on a well defined plane, the actual failure surface through the embankment material would <br />be a zone several ft or more in width which would distribute the strain in the liner over a similar <br />zone. Since VI.DPE liner can tolerate strains upwards of 1000 percent prior to rupture, it is entirely <br />possible that the liner would remain intact. In addition, the analyses inwrporated conservative sheaz <br />strengths for the embankment fill and fill to liner interface thereby resulting in codservatively lazge <br />displacements. <br /> <br />' July 13, 1993 12 SRK Projxt No. 14719 <br />