Laserfiche WebLink
<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 />An RCC tri a1 mi x was prepared usi ng materi a1 from the exi sti ng embankment. <br />The resu1 ts of comprehensi ve strength tests were unsati sfactory, probably due <br />to the micaceous nature of the weathered bedrock. An alternative source of <br />RCC aggregate, such as the glacial till deposits, would have to be evaluated: <br /> <br />The stability of the existing embankment was checked using the Modified Bishop <br />method for the downstream slope under steady-state conditions, and the <br />upstream slope during operational conditions. Material properties were <br />assigned based on laboratory test results and experience with similar <br />materials. The results of the stability analysis showed the upstream slope to <br />have a satisfactory factor of safety of 1.62 during rapid drawdown. Analysis <br />of the downstream slope, however, resulted in a factor of safety of 1.07, well <br />below the minimum standards for the steady- state condition of 1.5. <br /> <br />Seepage data, collected in 1984 while the reservoir surface was near normal <br />pool elevation of 9295, was studied in an attempt to determine major sources <br />of seepage. The maximum seepage, as measured by the two V-notch weirs <br />downstream of the embankment toe, approached 100 gpm. An approximate seepage <br />analysis utilizing laboratory permeability values, resulted in a total seepage <br />volume equal to only one tenth of that amount. Therefore, it is concluded <br />that the bulk of the seepage flow is being transmitted along the dam <br />foundation contact. <br /> <br />Based on the site inspections, geotechnical investigation, stability and <br />seepage ana1ysi s, and revi ew of the dam I s performance record, it was concl uded <br />that Twin Lakes Reservoir cannot be safely operated on an interim basis; due <br />to the instabil ity of the downstream slope and the condition of the outlet <br />works. Therefore, the current zero storage restriction should remain in <br />effect until such time as the structure can be rehabilitated. <br /> <br />In order to remove the SEO restri cti on, enlarge the dam, and restore the <br />reservoir to its decreed storage volume, and to operate the reservoir safely <br />in the future, a number of defi ci ences woul d have to be repai red. These <br />deficiencies are listed as follows, in order of importance to the safety of <br />the structure. <br /> <br />v <br />