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<br />. <br /> <br />. <br /> <br />. <br /> <br />. <br /> <br />0850 <br /> <br />6. Foundation, Q'Pl1d:l.:\;il;lnS. - The alluvium in the valley bottom where <br /> <br /> <br />the embankmeht would be placed, ranges from 20 to 30 feet in thickness. <br /> <br /> <br />On the abut!Jlsnts the soil mantle varies from a foot or so to 15 feet. <br /> <br /> <br />1he greater portion of the bedrock under the valley fill is soft shale <br /> <br /> <br />with comparatively low-strength values. Subsurface explorations indicate <br /> <br /> <br />that no serious foundation problems would arise if proper protection is <br /> <br /> <br />given to the 'shale beds dUring construction. Both abutments are on firm <br /> <br /> <br />sandstones and shcles with joint cracks in the sandstones due to river- <br /> <br /> <br />ward creep. An 8conomically balanced program of grouting and stripping <br /> <br /> <br />should prQvide a sound stable foundation for the proposed embankment. <br /> <br /> <br />7. Leaka.,e conditions. - It is possible that some leakage would <br /> <br /> <br />occur through sandstones 'of both abutments without a grout curtain; how- <br /> <br /> <br />ever, a suitable cut-off trench and grouting program ~Iould make a tight <br /> <br /> <br />structure. Any leakage that would occur would not be serious in that it <br /> <br /> <br />would not progressively increase., No large amount of seepage is antici- <br /> <br /> <br />pat'ed through the underlying shale. <br /> <br /> <br />8. Construction materials. - The material located in the borrow <br /> <br /> <br />areas as shown on plate 3 WQuld be suitable for the proposed structure. <br /> <br /> <br />Sufficient embankment material is a~ailable within a 2-mile radius of <br /> <br /> <br />the dam site. Rock excavation from the spillway and outlet works would <br /> <br /> <br />be'utilized in a 6-foot dumped rock blan1{et on the upstream slope of the <br /> <br /> <br />embankment. Concrete aggregate can be secured from Pueblo, COlorado, the <br /> <br /> <br />nearest source of acceptable aggregate. <br /> <br /> <br />9. Conclusions and recommendations. - <br /> <br /> <br />1. The construction of an earth dam at the Trinidad site <br /> <br /> <br />appears to be feasible from a geologic viewpoint. <br /> <br /> <br />2. Subsurface investigations indicate that the foundation con- <br /> <br /> <br />ditions are satisfactory and that there should be no detrimental leakage <br /> <br /> <br />if the abutments are properly sealed with a grout curtain, and postive <br /> <br /> <br />cut-off trench. <br /> <br />4 <br /> <br />AlYENDIX F <br /> <br />