Proceedings of the Deep Mixing 2015 Conference, (DFI)
Design Solutions for Seepage End-Around Effects at Cutoff Wall Depth Transitions
Michael Hughes, P.E., AECOM, United States; Ray Costa, P.E., G.E., Independent Consultant to California Department of Water Resources, United States; Selva Selvamohan, P.E., California Department of Water Resources, United States
Cutoff walls are commonly used to mitigate underseepage problems for levee remediation projects. At abrupt changes in seepage cutoff wall depths there is a potential for water to flow around the back of the deeper cutoff wall leading to elevated seepage pressures on the landside that could result in exit gradients exceeding design criteria. This condition is referred to as end-around-effects and is a complex problem that requires detailed and time consuming 3-D numerical modeling to represent accurately. This paper presents a simple approach for assessing end-around-effects using the results of 2D seepage analysis to determine if lateral extension of the deeper portion of the cutoff wall is required. This simplified approach provides a pragmatic solution to a complex 3-D problem. The presented procedure was used as part of the Feather River West Levee Project in Yuba City, California, to assess end-around-effects at 26 locations. The results showed that wall extensions of up to 100 feet were needed at only 2 locations.
|article #2030; publication #1013 (DM-2015)|