A particle-scale perspective on internal erosion: Observations from computational simulations and physical experiments

This study presents particle-scale insights into internal erosion mechanisms using computational simulations and physical experiments. Existing design criteria to determine the susceptibility of soils to initiation mechanisms, along with filter criterion for assessing continuation have been predominantly developed based on macro-scale observations. However, limited studies have explored the underlying particle-scale mechanisms. As internal erosion involves the detachment and transport of particles due to seepage, the mechanisms that lead to the initiation and continuation of erosion are rooted at the particle-scale. Computational simulations were performed using the discrete element method which investigated the stress distribution in gap-graded soils. A key finding is that under anisotropic loading conditions, certain transitional gap-graded soils can change from being fines-dominated to coarse- dominated, and hence, their susceptibility to suffusion may change under the anisotropic loading conditions. Physical experiments were conducted using a purpose-built coaxial permeameter cell that utilised spatial time domain reflectometry, an electromagnetic observational method which enabled near-continuous measurement of local porosity during the erosion process. This enabled physical insights into the changes in the internal structure of the soil during filtration experiments. By varying particle sizes and hydraulic boundary conditions, the influence of geometric and hydraulic criteria was investigated. These particle-scale findings can improve the robustness and reliability of existing tools, whilst leading to the development of new techniques to investigate and assess internal erosion.