Assessment of exit hydraulic gradients at the toe of levees in water drawdown conditions

The aim of this paper is to study the behavior of exit hydraulic gradients at the toe of homogeneous and isotropic levees, which are subjected to transient-state conditions caused by the water drawdown phenomenon. Unsaturated transient flow analyses are performed based on numerical modeling by the finite element method. Initially, an overview of the applied theoretical background is given. Afterward, with the purpose of obtaining a general panorama under different scenarios, the paper focuses on showing results of parametric analyses for computing exit hydraulic gradients assuming variable drawdown rates, soils with distinct hydraulic conductivities and different slope ratios of the levees. Additional calculations are carried out for demonstrating the usefulness of placing filters inside the levee in order to reduce soil erosion problems and increase the stability. Slope stability analyses are also executed by the Morgenstern-Price limit equilibrium method. Finally, conclusions and general recommendations drawn from the achieved analyses are provided.