Novel Undrained Servomechanism in Discrete-Element Modeling and Its Application in Multidirectional Cyclic Shearing Simulations

Abstract

Multidirectional shearing of granular soils involves shearing more than one shear stress component, and thus may result in more-complex soil responses than unidirectional shearing. This study developed an advanced numerical procedure that can impose an arbitrary loading path on a granular assembly in three-dimensional space as a basis for discrete-element simulations to investigate the behavior of granular assemblies under undrained cyclic multidirectional shearing conditions. The tests included varying stress trajectories on the deviatoric stress plane, including straight-line, circular, figure-8, and teardrop shapes. The numerical results indicated that the liquefaction resistance of a sample for a given cyclic shear stress ratio (CSR) depends on the stress orbits, and that of the teardrop shape was the highest and that of the figure-8 shape was the lowest. The microstructure of the granular assembly was quantified by the contact-normal-based fabric tensor, and its evolution trend correlation with stress–strain responses was explored. The evolution of fabric and stress–strain relationships from discrete-element modeling under multidirectional shearing conditions can provide useful insights into the behavior of granular soils.