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j. , . I . . I I I . . . I . I I . I I I 002656 Using this method, a series of trials was performed to determine the critical slip circles on the downstream slopes. The resulting critical downstream slip circle and factor of safety is presented in APPENDIX D. Upstream Slope Stability. The stability of the upstream slope of the dam was analyzed using . the total stress soil shear characteristics for the various mater- ials determined as previously discussed assuming rapid drawdown conditions. Pore pressures developed are accounted for in the total stress shear values and need not be derived for the rapid drawdown stability analysis. The same unit weight values and a similar method of analysis was used as presented above for deter- mination of the downstream slope stability. The resulting upstream slip circle and factor of safety is presented in APPENDIX D. As presented by Lambe and Whitman (Soil Mechanics, 1969, John Wiley and Sons) the effective stress soil shear characteristics were used for analysis of the downstream slope as would occur during steady state operation, and the total stress characteristics were used for the upstream analysis as during rapid draw down. Generally accepted practice requires the use of 1.5 as a minimum factor of safety where the soil shear strength parameters are known. The results of the analysis presented herein show the safety factors both upstream and downstream to exceed 1.5 by an acceptable margin. -5-