Evolution of Void Fabrics and Their Effects on Liquefaction Behaviors of Granular Soils: Insight from DEM-Clump Simulation

Previous studies have demonstrated that macroscopic liquefaction behavior is closely related to the evolution of the microstructure (fabric) of soils. Here we perform three-dimensional (3D) discrete-element method (DEM) simulations of soil liquefaction considering irregular shapes of Toyoura sand particles, which are approximated by 3D clumps. We introduce the Minkowski tensor to quantify the anisotropy of the particle-void cells around each clumped particle, and propose two void fabric proxies, E-d and A(d). The evolution of E-d and A(d) during the entire liquefaction process and their effects on pre- and postliquefaction behaviors are investigated. Specifically, E-d quantifies the shape elongation of particle-void distribution, while A(d )represents anisotropy of the particle-void orientation, which is closely correlated with the flow strain accumulation. We further quantify irreversible changes in fabrics and anisotropic load-bearing structures developed in liquefaction processes, and propose fabric-based criteria for jamming transition in flow deformation. The volumetric strain during reconsolidation is well correlated with E-d and A(d), whereas the jamming transition during liquefaction can only occur if Ad becomes sufficiently large. The interplay between strain, stress, and fabric evolution during pre- and postliquefaction will improve fundamental understanding and modeling of liquefied soils.