Breach Development and Core Failure during Overtopping of Zoned Embankment Dams

When a zoned embankment dam fails due to overtopping, each material zone affects the process of failure. To investigate the failure of each zone, and to study the effects of embankment material properties and core geometry on breach formation, an experimental study has been conducted. Eleven laboratory experiments were performed, in which embankment dams containing noncohesive shell and filter zones and a cohesive core zone were overtopped. The overtopping flow was observed to progressively erode the shell and filter zones downstream of the core, forming a breach channel that gradually expanded and exposed the downstream face of the core, reducing its stability against upstream water and sediment pressures. Under these pressures, the core bent, a vertical crack formed, and the core eventually separated along the crack. The separated parts subsequently broke due to cantilever rotation, resulting in a core breach. The breach formed faster for dams with thinner cores, and with the shell zone downstream of the core wetted. Equations describing core exposure at failure are proposed as a function of dam height, core thickness, and core water content.