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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 />PREVIOUS STUDIES <br /> <br />Smith Geotechnical, Fort Collins, prepared the Feasibility Study for Jackson Lake <br />Dam2 in 1993 to evaluate upstream slope protection options and to provide a <br />recommendation for the upstream slope maintenance and repair. The study was <br />performed in support of an application for a $1,000,000 loan from the CWCB. An <br />investigation of the dam embankment was conducted in 1992 as a part of the Smith <br />Geotechnical work. This study is included in Appendix E of the Smith Feasibility Study. <br />The investigation included drilling and sampling the embankment materials at locations <br />suspected of containing voids, or adjacent to areas experiencing sinkhole problems. <br />The work included a ground penetration radar survey into the embankment from the' <br />dam crest. No voids were definitively revealed. An attempt to evaluate the <br />embankment materials under the upstream slope surfacing failed. <br /> <br />The Smith report also included soil data from a subsurface investigation of the <br />dam embankment, an embankment slope stability analysis, and surveyed embankment <br />cross-sections that are useful in this current study. <br /> <br />.*., <br /> <br />In general, the dam embankment and dam foundation consist of fine sands and <br />non-plastic silty sands. Standard Penetration tests indicated blow counts of from two <br />to ten blows per foot. Laboratory testing indicated minus 200 fines in the range of <br />11 .6 percent to 43,5 percent. <br /> <br />The geologic map of the area indicates eolian deposits including dune sand, silt, <br /> <br /> <br />and loess. Units of the Pierre shale are present in the area principally on the north side <br /> <br /> <br />of the reservoir. <br /> <br />7 <br />