It has usually been assumed that the installation of cutoff barriers (slurry walls, concrete walls, secant pile walls, jet grouted walls, deep soil mixed walls, and sheetpile walls) results in permanent mitigation of seepage problems through embankment dams and foundations. Over the past year, we have collected long-term performance data from a large number of dams that have had seepage barriers in place for over 10 years. While most of these dams appear to be performing as expected, some have not. The most extreme example of unsatisfactory performance we have seen so far is Wolf Creek Dam in Kentucky, where a concrete diaphragm wall was installed between 1975 and 1979. Seepage problems at Wolf Creek Dam have redeveloped over the past 25 years to levels equal to or exceeding those observed prior to installation of the wall. Most of the seepage at Wolf Creek Dam appears to have developed beneath and around the wall and is thought to be the result of increased hydraulic gradients in these areas. The mechanisms leading to unsatisfactory long-term performance of earth dam seepage barriers can generally be attributed to the buildup of water pressure behind the wall and the associated increase in hydraulic gradient beneath, around and through the wall. The increased gradient can lead to internal erosion and piping in the dam and foundation. This paper will include a description of the study, a brief summary of the performance of the seepage barriers we have studied, and a description of the Wolf Creek Dam case.
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