1989-10-10_REVISION - M1988112 (12)

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loading conditions considered. The calculated Factors of Safety (FOS) are presented in the tables on Figures D.6-9 through D.6- • 12. The deposited tailings on the upstream slope of the embankment should act as a buttress under bath static and pseudostatic conditions. Under static conditions, the tailings will behave as a soil with fine grained material strength characteristics. Under pseudostatic conditions, given the low permeability of the tailings and the embankment materials, there is little likelihood the embankment will be either sufficient or be subject to any significant strength reduction. The tailings were conservatively modeled as.a low-strength soil under both static and pseudostatic cases. The upstream embankment slope stability will increase continuously with the rise in the tailings level. In the analyses, it was assumed that the phreatic surface corresponds with the tailings level at the upstream face of • the embankment. Because of the controlled deposition of the tailings and the design of the embankment, it is most unlikely that a hydrostatic head equal to the height of the tailings will ever occur. Therefore, a lower effective phreatic surface will exist through the embankment. Further, considering the pervious nature of the embankment drain layer, the downstream area is indicated to remain fully drained and stable for both short-and long-term stability. In all cases the calculated factors of safety met or exceeded the U.S. Army Corps of Engineers minimum factors of safety for earth and rock-fill as discussed in Section 0.3.5. D.6.8.3 North Dike The stability of the north dike has been analyzed as shown on Figure D.6-13. The stability analysis was limited to evaluation of the critical circular slip surface. Construction C~ D-68