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<br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />Free water was measured In the test holes at depths ranging from 19 to 24 feet at the time of <br />drilling or one day later. Information on long-term fluctuations of water levels in the test holes <br />Is not available; however, it Is expected that water levels In the test holes would vary <br />significantly with the reservoir levels. <br /> <br />5.3.4 STABIUTY OF EXISTING DAM <br /> <br />Our analysis of the stability of the existing dam included consideration of the history of the dam, <br />exterior slope and dam height, internal water level and subsurface soil conditions we found <br />within and beneath the dam. We evaluated this information as described below and selected <br />two Idealized study sections for our stabiltty analysis. We assumed soil parameters and Internal <br />water levels that we believe are reasonably conservative considering the history of the dam and <br />the variations in subsurface soil conditions found. <br /> <br />5.2.4.1 Study Sections <br /> <br />We evaluated two idealized study sections : the maximum section at about Station 3 + 00, <br />and at the seepage area at about Station 115 + 00. The upstream slope for the main <br />embankment averaged about 3:1 (horizontal to vertical), and the downstream slope ranged <br />from about 2.4:1 to about 4:1 on the lower portion of the slope. The exterior slope of the <br />study section taken at about Station 115+00 ranged from about 3:1 on the upstream slope <br />to about 2: 1 on the downstream slope. The dam height ranged from 42 feet at the <br />maximum section to 13 feet at about Station 115+00. Phreatic levels in the Idealized study <br />sections were based on knowledge of the history of the dam and the assumption that the <br />reservoir is returned to full storage capacity (gage height 34.5 feet). The study sections <br />used in the stability analysis are shown on Figure 11. <br /> <br />5.3.4.2 Stability Analysis <br /> <br />We considered standard penetration test results, triaxial test results and our experience for <br />selecting soil parameters for the stability analysis of the existing embankment. Earthquake <br />loading was simulated by psudo-statlc analysis using a seismic coefficient of 0.10. The <br />parameters used for the stability analysis are presented on Figure 11. The results of our <br />stability analysis, summarized on Figure II, indicate a minimum factor of safety of 1.6 for <br />static conditions and 1.4 with earthquake loading, thus the stability of the existing <br /> <br />5-11 <br />