Modeling the Erosion and Swelling of the Sides of Transverse Cracks in Embankment Dams

Abstract

Concentrated leak erosion occurs in transverse cracks in dams when the reservoir rises above the base of the cracks. As water flows through the crack, the sides of the crack will erode if the hydraulic shear stress exceeds the critical shear stress of the soil, and the crack will widen. For cracks above the phreatic surface, the sides of the partially saturated soil in the sides of the cracks will swell with increasing moisture content, narrowing the crack. These two phenomena occur concurrently. Laboratory erosion and swell tests have been carried out on five soils which are representative of the soils used in the core of embankment dams. Using this data and the equations controlling the rate of erosion, crack width versus time has been modelled. This shows that for the soils tested the crack will close for cracks up to about 5 mm wide for a flow gradient of 0.1, and 1 mm to 2 mm wide for a flow gradient of 0.4. For wider cracks the erosion will progress.