Jiangtao Wei

Evolution of Fabric Anisotropy in Cyclic Liquefaction of Sands

Cyclic liquefaction of sands is influenced by many factors including the initial fabric. Yet, it is difficult to quantify the soil fabric using laboratory technology. In this study, discrete element method (DEM) is used to numerically simulate the process of liquefaction under undrained cyclic loading. Samples with the same void ratio and varying degrees of fabric anisotropy are prepared by the pre-shearing method. Fabric evolution before and after cyclic liquefaction is quantified by the coordination number, angular distribution and the principal direction of inter-particle contacts. The DEM study demonstrated that the coordination number decreases and the fabric anisotropy increases gradually when the sand is cyclically sheared to approach the initial liquefaction. In this process, the principal direction of the anisotropic fabric tensor is not coaxial with the stress tensor. After initial liquefaction, all samples with different initial fabric evolve towards a same fabric, which is strongly anisotropic. The principal direction of the fabric aligns with the principal direction of the stress in the post-liquefaction stage.

Evolution of Packing Structure in Cyclic Mobility and Post-liquefaction of Granular Soils

Micromechanical change in packing structures can provide significant insights to better understand the cyclic mobility and post-liquefaction behaviors of granular soils. In this study, Discrete Element Method (DEM) is used to investigate the evolution of the packing structure under undrained cyclic loading. The coordination number is used to indicate the formation and destruction of a load-carrying structure in the post-liquefaction stage. A new index, termed as centroid distance, is proposed to quantify the effect of void and particle redistribution during cyclic loading. The new index is found to have a strong correlation with the mobilized maximum cyclic strain in post-liquefaction deformation.