Microstructural study of liquefaction in highly polydisperse granular media

During earthquakes, rapid loading on loose, water-saturated silty sands can lead to undrained (constant volume) conditions that induce high pore water pressures. This process, known as liquefaction in geotechnical engineering, involves a loss of stress in the solid phase (effective) and can result in structural failures, such as frequent mine tailings dam collapses. Understanding the particle-scale mechanisms behind liquefaction is crucial for predictive modeling. However, this aspect remains poorly explored due to experimental limitations. In this study, we use discrete element method (DEM) simulations on one highly polydisperse granular material to investigate liquefaction. Samples of varying density are prepared by removing different amounts of floating particles (rattlers) after consolidation. The samples are then sheared under constant volume to the critical state. The results show that loose samples lose all strength, medium-loose samples temporarily liquefy but regain strength at large strains, and denser samples do not liquefy and exhibit continued shear strain hardening. At the micro-mechanical scale, permanent liquefaction is linked to heterogeneous solid fraction distributions (macropores), while samples with uniformly distributed local solid fraction either resist liquefaction or recover from it.