Erosion-driven earth dam failure: A two-phase multi-state smoothed particle hydrodynamics model

Earth dam failures are typically triggered by overtopping, involving complex soil–water interactions and progressive structural collapse. Empirical and semi-empirical models provide efficient estimates of breach parameters and outflow hydrographs, but they usually offer limited resolution of the local stress state, rheological transition, and morphology evolution during overtopping-induced erosion. In this study, a graphics processing unit-accelerated two-dimensional, two-phase dam failure numerical model has been developed based on the Drucker–Prager yield criterion and weakly compressible smooth particle hydrodynamics. Combined with the Herschel–Bulkley–Papanastasiou (HBP) rheological model, the two-dimensional framework represents the yield-stress and strain-rate-dependent behavior of yielded soil during overtopping erosion. Stable inflow boundary conditions are established to simulate overtopping-induced erosion, entrainment, and subsequent transport of yielded soil particles by the water flow. Different failure modes of earth dams with different power law indexes are simulated. By comparing with experimental data, it can be observed that the model captures the key physical phenomena of scour thickening and “headcut” on the downstream slope. A transition in the modeled mechanical response of the eroded soil at the soil–water interface is identified, where the material changes from an unyielded state governed by the Drucker–Prager criterion to a yielded flow state described by the HBP model. Furthermore, the study findings indicate that the migration of fine particles and the rheological evolution of yielding soil during the erosion process lead to a reduction in the strength of earthen dams, which in turn accelerates the expansion of breaches.