Macro-Meso Mechanical Behavior of Loose Sand under Multi-Directional Cyclic Simple Shear Tests

Loose sand samples under different complex shear paths and directions of consolidation shear stress were simulated using bi-directional simple shear DEM models. Liquefaction characteristics and corresponding meso-mechanisms were analyzed, and the following conclusions were drawn. Bi-directional cyclic shear stress accelerated the drop in vertical stress, especially in the first and last cycles. Compared to uni-directional cyclic simple shear tests, the contact force between particles decreased faster in bi-directional cyclic simple shear tests. With an increased ?, the skeleton of the sample became unstable, and more particles were in a floating state, making the sample easier to liquefy. The mechanical coordination number decreased rapidly at the beginning and the end of shearing, and was relatively stable in the middle; it was around 4.2 when samples were liquefied. The magnitude of the anisotropy tensor gradually increased during shearing. Under bi-directional shear paths, the sample's skeleton structure was subjected to a greater disturbance during the initial shear stage, caused damage to the particle skeleton and faster liquefaction. With an increased ?, the amplitude and peak value of the anisotropy tensor increased.

Automated summary

Loose sand samples under bi-directional simple shear DEM models were simulated to study the liquefaction characteristics and meso-mechanisms. Results showed that bi-directional cyclic shear stress accelerated the drop in vertical stress and decreased the contact force between particles. An increased ? led to sample instability, increased floating particles, and easier liquefaction. The mechanical coordination number decreased at the beginning and end of shearing and was stable in the middle. The anisotropy tensor magnitude and disturbance to the skeleton structure increased under bi-directional shear paths.