Numerical investigation of mode failures in submerged granular columns

TL;DR

This paper uses a two-fluid numerical model to investigate failure modes of submerged granular columns, revealing how initial packing affects collapse dynamics and predicting breaching phenomena relevant to natural and engineered slopes.

Contribution

The study introduces a two-phase flow numerical approach to simulate granular column failures, capturing the effects of initial packing density on collapse behavior and breaching processes.

Findings

Loosely packed columns rapidly collapse due to positive pore pressure.

Densely packed columns stabilize and collapse slowly due to negative pore pressure.

The model accurately predicts breaching and turbidity currents in large-scale scenarios.

Abstract

In submerged sandy slopes, soil is frequently eroded as a combination of two main mechanisms: breaching, which refers to the retrogressive failure of a steep slope forming a turbidity current, and, instantaneous sliding wedges, known as shear failure, that also contribute to shape the morphology of the soil deposit. Although there are several modes of failures, in this paper we investigate breaching and shear failures of granular columns using the two-fluid approach. The numerical model is first applied to simulate small scale granular column collapses with different initial volume fractions to study the role of the initial conditions on the main flow dynamics. For loosely packed granular columns, the porous medium initially contracts and the resulting positive pore pressure leads to a rapid collapse. Whereas in initially dense-packing columns, the porous medium initially dilates and negative pore pressure is generated stabilizing the granular column, which results in a slow collapse. The proposed numerical approach shows good agreement with the experimental data in terms of morphology and excess of pore pressure. Numerical results are extended to a large-scale application known as the breaching process. This phenomenon may occur naturally at coasts or on dykes and levees in rivers but it can also be triggered by humans during dredging operations. The results indicate that the two-phase flow model correctly predicts the dilative behavior and, the subsequent turbidity currents, associated to the breaching process.