Strength anisotropy of granular material consisting of perfectly round particles

Abstract

The strength anisotropy of granular materials deposited under gravity has mostly been attributed to elongated particles' tendency to align long axes along the bedding plane direction. However, recent experiments on near‐spherical glass beads, for which preferred particle alignment is inapplicable, have exhibited surprisingly strong strength anisotropy. This study tests the hypothesis that certain amount of fabric anisotropy caused by the anisotropic stress during deposition under gravity can be locked in a circular‐particle deposit. Such locked‐in fabric anisotropy can withstand isotropic consolidation and leads to significant strength anisotropy. 2D discrete element method simulations of direct shear tests on circular‐particle deposits are conducted in this study, allowing for the monitoring of both stress and fabric. Simulations on both monodispersed and polydispersed circular‐particle samples generated under downward gravitational acceleration exhibit clear anisotropy in shear strength, thereby proving the hypothesis. When using contact normal‐based and void‐based fabric tensors to quantify fabric anisotropy in the material, we find that the intensity of anisotropy is discernible but low prior to shearing and is dependent on the consolidation process and the dispersity of the sample. The fact that samples with very low anisotropy intensity measurements still exhibit fairly strong strength anisotropy suggests that current typical contact normal‐based and void‐based second‐order fabric tensor formulations may not be very effective in reflecting the anisotropic peak shear strength of granular materials. Copyright © 2017 John Wiley & Sons, Ltd.

3D DEM simulation of principal stress rotation in different planes of cross‐anisotropic granular materials

“…There are three main methods for imposing boundary conditions in DEM simulations: (1) rigid wall, (2) periodic boundary, and (3) flexible boundary. Rigid walls are the most widely used type of boundary . Li and Yu performed two‐dimensional DEM simulations of PSR with polygon samples enclosed by rigid walls.…”

“…Rigid walls are the most widely used type of boundary. 14,15,17,28,[30][31][32][33] Li and Yu 15 performed two-dimensional DEM simulations of PSR with polygon samples enclosed by rigid walls. Periodic boundaries 26,[34][35][36] are widely used to reduce the boundary effects induced by rigid walls.…”

Dependency of Dilatancy Ratio on Fabric Anisotropy in Granular Materials

“…In this study, 2D DEM biaxial tests are conducted using the Polyarc Parallel-processing Discrete Element Modeling code (PPDEM) , which has been successfully applied to a number of studies on the mechanical behavior and fabric anisotropy of granular materials (Fu and Dafalias 2011;Wang et al 2016Wang et al , 2017aWang et al , b, 2019. 3D DEM triaxial tests are conducted using Yade (Šmilauer et al 2015), a widely used open source code (e.g., Kozicki et al 2013;Zhao and Guo 2015).…”

Discussion of “Description of Inherent and Induced Anisotropy in Granular Media with Particles of High Sphericity” by M. Oboudi, S. Pietruszczak, and A. G. Razaqpur

“…Using the simulation method described in detail by Fu and Dafalias (2011b), the discussers conducted a series of direct shear simulations on monodispersed circular-particle (D = 0.8 mm) granular material using twodimensional (2D) DEM (Cundall and Strack 1979); the results (Fig. 3) show vivid evidence of the strength anisotropy within granular materials with perfectly round particles, with a more than 20% difference between the maximum and minimum peak friction angles (Wang et al 2017).…”