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

Abstract

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 θ, 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 θ, the amplitude and peak value of the anisotropy tensor increased.