16 / 2025-04-24 11:27:18

Internal erosion at the contact between different materials in earthfill zoned dams: numerical simulation and review of empirical criteria

Particles migration and internal erosion phenomena occur if soil particles are dragged by seepage forces through embankments (e.g., at the contact between core and downstream materials) and foundation soils, from embankment to foundations, around and into pre-existing conduits within embankments. The granulometric stability at the contact between materials characterized by different grain size distribution (i.e. B-T systems) plays a key role in safety of zoned embankment dams as shown by historical failures and incidents.
The the granulometric stability of a fine-grained base material (B) requires a correctly designed protective granular transition material (T) whose voids, related to the grain size distribution (GSD) and porosity, must be small enough to stop the migrating particles of B within short distances (formation of “natural filter”), and simultaneously allow a safe drainage of B to prevent the occurrence of limit states (piping, clogging, blinding….).
The available (empirical and analytical) methods to analyze particle migration phenomena at the contact between different materials generally don’t take into account the coupled effects of the involved geometrical and hydraulic variables (e.g. GSD, porosity, volume voids distribution, permeability, piezometric gradients, seepage velocity….), as well as their progressive space-time evolution. Thus, a numerical procedure allowing to simulate coupled 1D seepage and particle migration processes, depending on both geometrical and hydraulic governing variables, as well as on their mutual dependency, has been developed and applied (for its validation) to a detailed analysis of the well-known Terzaghi’s criteria as well as subsequent methods derived from it.
The proposed procedure may be applied to design protective granular transitions as well as to predict undesirable phenomena that might evolve up to limit states.