Explanations of anisotropic strength and fabric evolution in granular soils by DEM simulations and buckling failure theory

Abstract

ABSTRACT This research aims to discover a micro explanation of anisotropic strength of granular soils caused by different inherent fabrics based on the discrete element method (DEM) simulations. Soil particles are simulated as ellipsoids (i.e., clumped spheres) to preserve the elongation distributions of real soil particles that are determined by analysing 90,000 particles from 18 sands. Then, virtual soil specimens are prepared at 12 different inherent fabrics by restricting the particle long axis orientations. For each inherent fabric, triaxial tests are simulated at five intermediate stress ratio values, resulting in a total of 60 DEM simulations. The relationships between anisotropic shear strength and fabric evolution are investigated based on simulation results. For a specific inherent fabric, Lade’s isotropic failure theory can be used to describe shear strengths and octahedral contact normal fabric factors at peak and critical states. A buckling failure theory from structural engineering is introduced to explain the anisotropic strength of granular soils and fabric evaluations observed in laboratory tests and simulations. As the angle between loading and fabric direction increases from zero to 90 degrees, the conceptual widths of soil columns decrease, leading to the smaller buckling failure loads and therefore the smaller shear strength of granular soils.