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Micromechanical modeling provides significant insight into the fundamental mechanism of soil liquefaction. In this study, a series of undrained cyclic simple shear simulations were conducted by using discrete element method (DEM). The particle-scale information provided by DEM was used to quantify the local void distribution around particles. Two microscale descriptors, named as the shape-elongation descriptor (Ed) and the orientation-anisotropy descriptor (Ad), were proposed to quantify the overall anisotropy of local void distribution in the granular packing. Before initial liquefaction, the particle-void distribution remains to be globally isotropic for isotropically consolidated samples. An irreversible development of anisotropy in terms of Ed and Ad mainly occurs in the post-liquefaction stage. In addition, jamming transition of the liquefied soil is determined by using these descriptors because a unique hardening state line (HSL) is found in the Ed−Ad space that can differentiate a post-liquefaction flow state from a hardening or jamming state. Furthermore, large post-liquefaction flow strains are found to be closely correlated to the descriptors. [ABSTRACT FROM AUTHOR]

The drag force law acting on a moving circular disk in a two-dimensional granular medium is analyzed based on the discrete element method (DEM). It is remarkable that the drag force on the moving disk in moderate dense and pure two-dimensional granular medium can be well reproduced by a perfect fluid with separation from the surface of the tracer. A yield force, being independent of the moving speed of the disk, appears if a dry friction between the granular disks and the bottom plate exists. The perfect fluidity is violated in this case. The yield force and the drag force diverge at the jamming point. [ABSTRACT FROM AUTHOR]