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"D" Seam Slope Stability Paqe 4 October 19, 1998 Section 7300 sliding surface. Factors of safety are provided for an assumed completely dry slope condition and for a fully saturated • slope condition. The dual analysis was necessary to verify the conservative nature of the assumptions previously described. If the factors of safety for the saturated slope condition were greater than one, the assumed shear strength values would be too high to correctly predict the slope failure that occurred. The fact that the rock mass slid after part of the toe of the slope was removed during road construction demonstrated that the 1976 ground surface factor of safety had to be less than one, which is correctly predicted by the preliminary analysis. The Section 7300 dry slope factors of safety for the 1976 ground surface slide mass segments are all greater than one. with the exceptions of Segment Ib at the crest and Segment VIb near the toe, saturated segment factors of safety are less than one. The overall Section 7300 slope factors of safety for the 1976 ground surface, shown on the last page of Table 1, indicate stability for a dry slide slope (FS = 1.32) and predicts failure of the fully saturated slope (FS = 0.90). The analysis predicts that the Section 7300 slope failed before the slope was fully saturated, i.e. when the uplift pore pressure reduced the frictional resin tance to sliding to less than the calculated downslope thrust. The impact of the planned excavation of part of the slide mass above the Section 7300 sliding surface, indicated by the "cut • surface" curve on Figure 1, is considerable. None of the "cut surface" segment factors of safety drop below one, even when the remaining slide mass is assumed to be saturated. The overall saturated slope factor of safety increases to 1.50 for the "cut surface" slope analyzed from 0.90 for the 1976 ground surface slope. The first page of Table 2 presents the calculated factors of stability for the six individual segments along the estimated Section 7450 sliding surface. Factors of safety are provided for an assumed completely dry slope condition and for a fully saturated slope condition. The dual analysis for Section 7450 further verifies the conservative nature of the assumptions previously described. Not all the factors of safety for the saturated cut slope segment condition are, however, greater than one. The calcu- lated factor of safety for saturated Segment IVa cut slope is 0.87, indicating that failure is a possibility within Segment IVa if the cut slope becomes saturated. However, the high saturated factor of safety of downslope Segment Va (FS = 1.41) should protect the "D" Seam portal area. Failure of Segment IVa slope after excavation to the cut surface should result in the sliding surface rising to the cut surface and possibly overriding the upper part of the Segment Va cut surface.