Assessment of Potential for Seepage-Induced Unraveling Failure of Flow-Through Rockfill Dams

Abstract

A purely numerical parametric study of 24 flow-through rockfill dam geometries was conducted. The nonlinear nature of the p-LaPlacian–like partial differential equation was dealt with using a finite-difference scheme that directly incorporated the exponent of a power law that replaced Darcy’s law. Convergence, use of specialty nodes, nodal density, and boundary condition effects were quantitatively investigated. The flow-field angle of the toe was found to be a useful starting point in studying the potential for unraveling failure. Factors of safety (FS) against this type of failure are then presented for a range of downstream slopes, thus showing which combinations of slope and particle diameter are unsafe. It is shown that the FS tends to drop below unity under the seepage face primarily because of the strength of the exit gradient near the toe of the structure and secondarily because of the overflow velocity. It is hoped that the techniques and results presented will facilitate the design and assessment of flow-through rockfill structures.