1989-10-10_REVISION - M1988112 (12)

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D.6.8.2.1 Analyses Criteria • The embankment cross-section illustrated on Figures D.6- 9, D.6-10, and D.6-12 represent the critical section analyzed for stability purposes. The stability of the upstream and downstream faces was evaluated assuming several possible conditions during operation. The worst-case-scenario for the upstream face occurs prior to tailings deposition. The stability analysis for the downstream face is considered to be critical when the impoundment is filled to capacity with tailings. In considering the stability of the downstream face, it has been assumed that the phreatic surface was confined to the pervious drainage layers. This assumption is considered valid as the relative permeability of the construction material to the tailings is such that unsaturated conditions will be maintained within the embankment fill. • The cases selected for the embankment stability analyses are shown on the aforementioned figures, and acre summarized as follows: Case 1: Phase 1 embankment; Case 2: Raise 1, Phase 2 embankment; and Case 3: Raise 2, Phase 2 embankment. The embankment is to be constructed on a foundation that slopes at approximately 3.0 percent. The area beneath the embankment will be completely lined. To estimate the planar stability along the liner interface, an analysis was also performed to determine the potential for instability using a sliding wedge analysis. The potential for instability of the embankment under seismically-induced loading was evaluated by using a pseudostatic analysis. A pseudostatic analysis models • instantaneous seismic accelerations as static forces applied D-65