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-; Ms. Honey R. Moschetti, President -5- December 19, 1994 1. The observed poor condition of the raise section, substantiated by the results of the 1986 core tests. 2. This section presents the greatest concern to the SEO, as discussed in several recent inspection reports. The analyses were performed using classical two-dimensional gravity methods. The two- dimensional gravity approach results in a conservative evaluation of the ability of the raise section to withstand various levels of overtopping. A conservative analyses will result in an estimate of the maximum adverse forces acting on the dam, and hence the lowest level of overtopping that could cause sliding or failure of the raise section. Our experience suggests that the analyses will not to predict the actual behavior of the raise section; and that the dam may be capable of withstanding greater levels of overtopping. A prediction of the actual behavior of the structure would require a more rigorous analysis which would consider the true three-dimensional behavior of the entire dam. The following assumptions were used in our simplified analyses: 1. Sliding stability was evaluated at the contact surface ("joint") between the original dam and the base of the raise section (at gage height 30.1). Stress and stability conditions at this location are the most severe in the section because of the relatively weak concrete in the lower concrete raise section, and because of the higher loads applied at this location of the section. 2. The effects of vertical water loads on the crest and downstream face of the raise section during overtopping were not included. 3. The effects of cohesion at the base of the raise section (gage height 30.1) were not included in the sliding stability calculations. Cohesion at this location would require adequate bonding of the concrete in the raise section to the surface of the original dam crest. Meaningful estimates of the effective bond at this surface would require knowledge of the surface preparation techniques employed during construction of the raise, or field test data showing actual conditions at the joint. This information was not available for use in our analyses. 4. Sliding stability analyses were performed with values of the static coefficient of friction (Il) of 0.6 and 0.7 at the base of the raise section. For simplicity, only the analysis results for Il equal to 0.7 are reported. 5. The unit weights for the concrete were taken as 135 pounds per cubic foot in the lower portion of the raise section (gage height 30.1 to gage height 34.1), and 149 943IJIDDREI'ORT.L 11l.