Bimodal character of induced anisotropy in granular materials under undrained shear

Granular anisotropy is attributable to many complex behaviors of granular materials and reflects important microstructures at the grain scale, and should be fully considered towards the development of realistic constitutive models for such materials. In this paper, we present a study on the behavior of anisotropy using a three-dimensional Discrete Element Method (DEM). Isotropic packings of sand with different initial states are sheared to large strain under undrained conditions. The bimodal character of force transmission and induced anisotropy in the granular assembly is carefully examined. Under some conditions, such as when liquefaction occurs, it is found that certain degree of geometric anisotropic may develop in the weaker-than-average force network, wherein the mechanical anisotropy remains largely small. The study helps to improve our understanding on granular materials, and will be useful for geotechnical applications.