Probing Fabric Evolution and Reliquefaction Resistance of Sands Using Discrete-Element Modeling

Abstract

Recent case histories have demonstrated that soil liquefaction can occur repeatedly at a site during a sequence of earthquake events. Field observations and laboratory tests imply that reliquefaction resistance can be markedly different, depending on the strain histories and induced fabric change. However, direct observation of fabric evolution during the entire process remains limited. In this study, we perform simulation using a three-dimensional (3D) discrete-element method (DEM) to quantify fabric evolution in granular soils during liquefaction, reconsolidation, and reliquefaction processes, with the goal of investigating the effects of fabrics on reliquefaction resistance. Clumped particles are used to construct realistic particle shapes of Toyoura sand in the DEM, and soil fabric is characterized by a coordination number Z and a degree of anisotropy ac. By reconsolidating samples at different states after the first liquefaction, we describe the relationships between the maximum preshear strains versus volumetric compression and the resulting soil fabrics (Z, ac) after reconsolidation. Finally, we set up correlations between the reliquefaction resistance and soil fabrics (Z, ac). This study shows that the effects of strain histories on reliquefaction resistance are intrinsically attributed to changes in soil fabrics before and after reconsolidation. The DEM simulation also generates data that are consistent with laboratory tests and provides micromechanical insights into the reliquefaction phenomenon.