Fabric evolution and liquefaction resistance in multiple-liquefaction process: a micromechanical study using DEM-clump

Recent earthquake case histories in Japan and New Zealand revealed that soil sites can experience liquefaction multiple times under a sequence of earthquake shaking. Field observation showed that the reliquefaction resistance of granular soils can be considerably different. Although geotechnical community has known that fabric change during the liquefaction and reconsolidation process may be responsible for the vastly different reliquefaction resistance, direct observation of fabric change over multiple-liquefaction stages has been rarely achieved in previous studies. In this study, 3D clumped DEM simulations are conducted to trace the microstructure evolution of soils in the multiple-liquefaction process. The use of clumped particles enables generation of soil samples with realistic particle shapes, initial void ratios and reconsolidation process, which is particularly important for modeling multiple-liquefaction phenomenon. Cyclic liquefaction and reconsolidated tests are carried out alternately until ten times, while fabric evolution and its connection to volumetric compression are characterized, seeking a linkage between soil fabric anisotropy and liquefaction resistance in multiple stages. This study reveals that strain history has a significant effect on the liquefaction resistance Nliq\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$N_{{{\text{liq}}}}$$\end{document} during multiple stages. Ultimately, a unified multiple-liquefaction resistance relationship is established by introducing soil fabrics Z and ac\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$$a_{c}$$\end{document} for all liquefaction tests, providing a critical link between fabric and liquefaction resistance in multiple-liquefaction process.