Featured Application The failure analysis of soil in the field of geotechnical engineering.Abstract The localization of deformation in shear bands is a fundamental phenomenon in granular materials like soil. In this study, we focus on the characteristics of shear bands, particularly the size effect, by implementing biaxial discrete element method (DEM) modeling. Firstly, we describe the establishment of the biaxial experimental model with dense sands. Then, we implement analyses of specimens with different sizes and find that there is a clear size effect in the stress-strain curve after the peak strength point, and there is less of a size effect in the angle of the shear band; the angle is consistent with Arthur's theory. Finally, the reason for the size effect is analyzed using the width of the shear band and the porosity inside the shear band. As the specimen size increases, the ratio between the shear band area and the whole specimen decreases. This effect reduces as the isotropic confining stress increases. The difference in the proportion of the shear band area mainly causes the size effect that affects the specimen deformation characteristics. We also find that with the increase in isotropic confining stress, the type of shear band gradually changes from cross-type to single-type. Our study provides valuable insights into understanding the behavior of granular materials.

Applying the discrete element method (DEM) in soil mechanics can provide abundant information at the particle-scale and facilitates illustration of the macro-mechanical behaviour of soils based on the interparticle mechanisms. The triaxial test is one of the most common laboratory methods to study the macro-mechanical behaviour of particulate materials such as soil. However, many problems in geotechnical design can be assumed and simplified as a plane strain phenomenon. Therefore a biaxial test can be conducted to reproduce the macro-mechanical behaviour of soil, where the sample is enclosed by two horizontal rigid platens and a vertical latex membrane, which is a deformable continuous element and allows the enclosed specimen to deform freely while maintaining confining stress during loading. This paper presents an algorithm to represent physical and mechanical characteristics of latex membrane in the 2D DEM simulation of biaxial test using the PFC2D code. To investigate the impact of the lateral boundary conditions on the micro-macro mechanical behaviours of soil samples, two sets of DEM biaxial tests are conducted, i.e. with rigid and deformable lateral boundary conditions. The DEM modeling results indicate that the lateral boundary conditions have a significant effect on the micro-scale fabric properties, thickness and inclination of the shear band. The comparison between these two simulations also demonstrates that the lateral boundary conditions play a major role in the peak and post-peak stress-strain behaviours as well as the dilation and critical state behaviours of granular soils.(c) 2023 Chinese Society of Particuology and Institute of Process Engineering, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.