*WINNER* Effect of levee foundation coefficient of consolidation on the extent of the saturated zone after flooding for rapid drawdown analysis

Abstract

As part of a broader research initiative exploring the extent of the saturation zone in levees due to flooding, this study investigates the effects of foundation properties on levee through-seepage. The coefficient of consolidation, cv dictates the response of levee and foundation soils to transient flow conditions and subsequently the extent of saturation in levees. Uncoupled transient seepage analysis from finite element methods was used to estimate parametrically the position of the phreatic surface in levees considering soil coefficient of consolidation, levee geometry and flood hydrograph. The results showed that the extent of the saturated zone for an impervious foundation was similar to that found for levees with cv higher than the foundation cv. The saturated zone tends to have an L-shape when a more pervious foundation is considered. Seepage from the retained water (Zone A) is not significantly affected by the presence of a pervious foundation. On the other hand, Zone B is influenced by the rate of seepage within the foundation and the levee properties. The results indicate that levee foundation conditions have the largest impact on levee through-seepage when the foundation has a higher cv than that of the levee itself. The study develops equations and chart which can be used to make appropriately conservative assumptions about the saturation zone within levees on pervious foundation prior to rapid drawdown. Cases where the levee has a higher cv than the foundation may be analyzed for RDD by assuming an impervious foundation.