An effective approach to prevent piping in older dams using cut-off walls construction/design

Recent studies have shown that the probability of failure of large embankment dams, that were constructed prior to 1986, is approximately 1.2% over the life of the dam, and that piping is responsible for approximately 46% of those failures. Piping incidents lead to failure approximately 34% of the time, and dams built before 1950 are 7.5 times more likely to fail by piping than dams built after 1950 [Saber et. Al, 2001]. When a dam is constructed without adequate filters and foundation treatments, the prevention of piping may require constructing a cut-off wall. The Hodges Village Dam (built in 1959) in Oxford, Ma., the Whitney Point Dam in Binghamton (built in 1942), N.Y., the West Hill Dam in Uxbridge (built in 1961), Ma. and the Vermont Waterbury Dam (built in 1938) are examples of projects, with seepage related problems, at which cut-off wall designs were implemented to prevent piping paths from undermining the structures. In this paper, the West Hill dam and the Waterbury dam rehabilitations are investigated, as case studies, in order to better understand how two different cut-off wall designs, Slurry Cut-off wall and the Secant Cut-off wall were employed to rehabilitate the dams. The Waterbury dam secant cut-off wall was discontinued after several issues with its construction developed; the design approach and the evolution of its rehabilitation through this process will be briefly mentioned.