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<br /> <br /> <br /> <br />5 <br />Case Studies – Repairs <br />Fish Lake, CO –This dam has a history of seepage <br />along the downstream toe, believed to be due to <br />the open matrix character of the foundation rock. <br />A sinkhole recently occurred on the upstream side <br />of the dam near the left abutment, presumably <br />due to voids most likely at the interface between <br />the dam embankment and the foundation. The <br />sinkhole was first observed during a routine <br />inspection in July 2011. Further inspection and dye <br />testing by a geotechnical engineer in October 2011 <br />confirmed the location of the entrance and exit <br />point of the seepage flowing from the toe of the <br />embankment. The use of urethane grout was <br />recommended to fill the sinkhole. Grouting took <br />place in August 2012. <br />The sinkhole was first cleared of rock and debris <br />and then flushed with approximately 5 gallons of <br />water to obtain thorough pre-wetting for the grout <br />application. <br /> <br />Photo 5: Flushing of sinkhole at Fish Lake, CO <br />The application of the grout into the sinkhole was <br />aided by a steel pipe and tarp to funnel the material. <br />Stratathane ST-504 Vari-Gel Injection resin was used. <br />Lake water was used for flushing and mixing the grout. <br />The grout was applied in stages with three different <br />mixes, becoming more viscous with each application. <br />The mixes were: <br />• 15 water to 1 grout: 30 gallons of water <br />applied, grout completely absorbed, poured <br />easily. <br />• 10 water to 1 grout: 30 gallons of water <br />applied, grout completely absorbed, some <br />backing up during pouring. <br />• 5 water to 1 grout: 5 gallons of water applied, <br />grout was not entirely absorbed, pipe <br />containment was half full. <br /> <br />Photo 6: Final application of grout, contained within pipe (Fish <br />Lake) <br />The most fluid mixture took longer to set up before the <br />next application could be poured, but obtained the <br />greatest penetration into voids or cracks related to the <br />sinkhole and seepage path. The second and third <br />application took less time to set up but obtained less <br />penetration. All mixtures expanded upon application <br />and the last mixture served to cap the sinkhole. After <br />the grout had set up and cured, the pipe was removed <br />and the area was backfilled with rock to provide <br />protection for the grout. An inspection 6 months after <br />the grout application found some shrinkage of the <br />grout at ground surface, but the sinkhole appeared to <br />be sealed. No issues have been reported around the <br />sinkhole or in other areas of the dam since the repair. <br />Lake Ann, CO – Seepage 400 feet downstream of the <br />dam has been a longstanding issue at Lake Ann. <br />Evidence indicates water was flowing through the <br />foundation of the dam from upstream. A sinkhole from <br />the 1960s was repaired with a plastic liner. <br />Deteriorated plastic was found and removed in the <br />excavation of a more recent sinkhole in the same area. <br />The recent sinkhole was observed at the dam <br />approximately 15 feet upstream of the intake and 100 <br />feet right of the outlet. The flow was approximately 0.3 <br />cubic feet per second when initially measured in <br />October 2014. The reservoir was immediately drained