Internal Instability of Granular Soils at Particle Scale: A DEM Analysis

Internal instability establishes when fine particles of bimodal soil migrate with seepage flow into voids created by coarse fabric, altering the original gradation. The tendency for soils to undergo internal instability centres on their compaction level and particle size distribution. This study employs the discrete element method to evaluate the potential for internal instability at the particle scale. Numerical simulations enable a thorough analysis of particle contacts in soils, encompassing both internally unstable and stable conditions. The study examines particle connectivity at different relative densities and uses particle connectivity and stress reduction factor to draw clear distinctions between soils that are internally unstable and those that are stable. Grain-scale data allows for a precise measurement of the stress reduction within the finer portion of the materials. The stress distribution is observed to be influenced by the particle-size distribution, percentage of finer fraction, and relative density. The predictions of the current numerical model align with the constriction-based criterion, enhancing practitioners’ confidence in a timely preliminary evaluation of soil internal instability potential.