Characterization of the Overtopping Flow through the Downstream Shell of Rockfill Dams

Abstract

In 1997, Toledo developed a numerical model to characterize the flow through the downstream shell of a rockfill dam for the overtopping scenario. He performed a parametric study focused on nondeformable, completely saturated dams and analyzed the effect of different geometric and rockfill parameters on the characteristics of pressure heads and throughflow, such as the infiltration and emergence lengths. This paper provides experimental validation of this theoretical work. Six physical models were tested in a flume, modeling the downstream shell of 1-m high rockfill dams and using three uniform gravels with D50 sizes varying between 0.0126 and 0.045 m. The conceptual frame developed by Toledo was confirmed, and the derived results allow the estimation of the minimum discharge needed for full saturation of the downstream shell, and also the determination of the pressure heads and the position of the first emergence point for that saturated state. Differences between the physical and numerical data varied around 23% for the saturation discharge and around 7.0% for the pressure head, and were reduced to 3.9% for the emergence length. Experimental observations were also used to fit new formulas for the phreatic surface profile. Future research is needed in areas related to the anisotropy of rockfill dams and the definition of nonlinear resistance laws based on the main characteristics of the rockfill.