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<br />I <br /> <br />I <br /> <br />I <br />I <br /> <br />I <br /> <br />Option 6B - Armor with Riprap <br />In this option, it is proposed to leave the existing concrete facing in place to <br />provide a seepage barrier in the embankment. Because the riprap facing is flexible, <br />minor settlement of the existing slabs would not impact the serviceability of the riprap. <br />A major program to investigate voids under the existing slabs would be undertaken. <br />This program would include drilling into the slabs and probing for voids. If voids were <br />encountered, the site would be further explored. It is expected that the voids would be <br />grouted, but in some cases it may be necessary to entirely remove the existing slabs. <br />The toe wall foundation would be constructed of riprap and bedding materials. A riprap <br />layer 36 inches thick is recommended, with the 050 rock size of 24 inches. Granitic <br />riprap would be imported from the front range area and riprap bedding imported from <br />nearby gravel pits in the Greeley or Fort Morgan area. <br /> <br />I <br /> <br />I <br />I <br /> <br />I <br />I <br /> <br />Riprap placement is a conventional installation for upstream slope protection. <br />The primary problem is the extensive distance to potential rock and gravel sources, and <br />the cost to haul these materials. Rock riprap is expected to last 100 years with <br />occasional routine maintenance. The issues of possible voids and/or loose soils under <br />the facing producing settlement are addressed adequately with the void investigation <br />and the inherently flexiqle n'3tur~ of the riprap.. The dam embankment stability issue is <br />addressed with the flattening of the slope. The seepage issue is acceptably addressed <br />by leaving the existing slabs in-place (rock riprap does not provide any seepage control). <br />Selective borrow of silty-clayey soils for the embankment flattening may also help <br />reduce the potential for excessive seepage through the embankment. The expected <br />long construction duration is expected to impact the ability to use and/or store water. <br /> <br />I <br /> <br />I <br /> <br />I <br />I <br /> <br />Proiect Costs <br /> <br />I <br /> <br />The preceding section . described the repair alternatives, and qualitatively <br />discusses durability, longevity, maintenance issues, and other uncertainties associated <br />with t~e alt~rnatives. The primary project evaluation factors are overall project cost, <br />including consideration of maintenance and life span, and perceived risk due to untried <br />and/or unproven applications. For all alternatives except Option 1 - Do Nothing, where <br />severe water storage restrictions are expected, there is no difference in the project <br /> <br />I <br />I <br />I <br />I <br /> <br />32 <br />