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-13- <br />n <br />U <br />conditions the maximum depth of water and sediment will be on the <br />order of 10 feet. Additionally, the structure is planned with a <br />life expectancy in the range of 15 to 20 years. Saturation of <br />the embankment will probably not occur above elevation 30. Con- <br />sidering the short duration of the 10-year event and the time of <br />containment of a 100-year event, a 2:1 slope would be stable on <br />both the upstream and downstream sides for the height embankment <br />planned. However, the relatively soft underlying foundation clays <br />control the design. We recommend side slopes of 3:1 on both the <br />upstream and downstream sides of the embankment. A minimum crest <br />width of 12 feet is recommended for convenience of construction. <br />The embankment drain is recommended to control seepage conditions <br />• in the downstream portion of the embankment. <br />Stability Ana~sis <br />Strength parameters for the proposed embankment and foundation <br />soils were established on the basis of laboratory testing and our <br />experience. A graphical method of slices, as well as a computer <br />method based on Spencer's technique, were used to evaluate the <br />relative stability of the embankment and the foundation. Our cal- <br />culations indicate the recommended embankment section should be <br />stable, both during and after construction. A summary of the results <br />of our stability analysis is presented on Fig. 10. For this par- <br />ticular embankment, the most critical condition will occur at the <br />• end of construction when the maximum load will have been transferred <br />