Downstream filter control of flow in cracks in embankment dam cores

A major hazard to embankment dams is internal erosion and piping arising from concentrated leaks through transverse cracks in the core near the crest due to differential settlement or desiccation. Erosion is controlled by the wall stresses resulting from flow in the crack, the critical shear stress, and rate of erosion properties of the soil. Many older embankment dams have filters or transition zones downstream of the core to arrest erosion, but the filter or transition is coarser than required to satisfy modern no-erosion filter design criteria, so erosion potentially initiates and progresses. We previously presented an analysis of flow through such transverse cracks without a filter, applicable to homogeneous embankments. This present analysis models flow in embankment cracks with a vertical filter downstream. Capillary and adhesion processes are neglected. Multiphase flow computations are avoided by assuming that the filter is saturated and then demonstrating that pressure along the separating streamline between the crack discharge and the saturated zone is ∼0. The consequent water levels and hydraulic shear stresses within the cracks are then determined. Plausible methods for adapting the assumed geometry and flow conditions to other commonly-occurring arrangements are also presented.