Particle shape is an intrinsic characteristic of soil particles that significantly influences mechanical responses. In this investigation, a meticulously calibrated and validated two-dimensional discrete element method (DEM) model of a biaxial shearing test was employed to simulate the shearing response of forty distinct particle shapes. The systematic evolution of particle roundness (R) and aspect ratio (AR) was achieved by utilizing idealized polygonal-shaped particles, aiming to comprehend their effects on the macro and micromechanical behaviors of granular materials. The results suggest that a reduction in R limits free rotations and enhances interlocking, thereby promoting relatively stable force transmission between particles and leading to a monotonic increase in shear strength. However, this effect diminishes as particles become more elongated. Conversely, a decrease in AR from 1.0 (increased elongation) constrains particle rotations, increases the coordination number, and enhances fabric anisotropy initially resulting in increased overall shear strength, reaching a maximum before exhibiting a decreasing trend, indicative of non-monotonic variation. For high elongations, notable fabric anisotropy impedes clear force transmission between particles thus facilitating interparticle sliding and overall strength diminishes. The extent to which AR impacts depends on the angularity feature of particles. Finally, a nonlinear equation has been proposed to predict the variation in critical state shear strength of granular samples, based on the R and AR values of the constituent particles.

The shear strength and resistance of granular materials are critical indicators in geotechnical engineering and infrastructure construction. Both sliding and rotation influence the energy evolution of soil granular motion during shear. To examine the effects of particle rotation on shear damage and energy evolution in granular systems, we first describe the transformation of irregularly shaped particles into regular shapes via geometrical parameters, ensuring the invariance of energy density and density. We then analyze the impact of particle rotation on shear-stress variation and energy dissipation through a shear energy evolution equation. Additionally, we establish the relationship between the shear-stress ratio and normal stress, considering particle rotation. Finally, we verify the influence of particle rotation on energy evolution and shear damage through shear tests on irregular calcareous sand and regular silica-bead particles. The results indicate that granular materials do not fully comply with the Coulomb strength criterion. In the initial shear stage, most of the external work is converted into granular rotational-shear energy, whereas in the later stage, it primarily shifts to granular sliding-shear energy. Notably, the sensitivity of the granular rotational energy to a vertical load is significantly greater than that of the granular sliding energy.

The applicability of particle-scale modeling using the discrete-element method (DEM) is typically evaluated by comparing simulation results with stress-strain responses observed in elementary tests. This validation at the global level may not guarantee that the simulation can capture realistic particle-level motion. Thus, this study investigated the applicability and limitation of two types of DEM models, through the comparison with experimental results of biaxial shearing tests on bidisperse granular assemblies comprising circular (round) and hexagonal (angular) particles under various confining pressures. Experimental data wherein particle rotations were identified by novel image analysis technique were used to evaluate whether the DEM models could accurately reproduce macroscopic stress-strain relationships and microscopic particle responses. Experimental findings suggested that particle rotations play a crucial role in granular deformation and are influenced by the particle shape. A detailed DEM model with precise particle shapes effectively replicated both macroscopic stress-strain relationships and microscopic responses, including particle rotation and interlocking at global and local levels. Conversely, a simpler ad hoc DEM model, which incorporates rolling resistance for circular particles, could imitate the stress-strain relationships of hexagonal particles but fell short in replicating microscopic responses accurately.

PurposeThe objective of this paper is to quantitatively assess shear band evolution by using two-dimensional discrete element method (DEM).Design/methodology/approachThe DEM model was first calibrated by retrospectively modelling existing triaxial tests. A series of DEM analyses was then conducted with the focus on the particle rotation during loading. An approach based on particle rotation was developed to precisely identify the shear band region from the surrounding. In this approach, a threshold rotation angle omega 0 was defined to distinguish the potential particles inside and outside the shear band and an index g(omega 0) was introduced to assess the discrepancy between the rotation response inside and outside shear band. The most distinct shear band region can be determined by the omega 0 corresponding to the peak g(omega 0). By using the proposed approach, the shear band development of two computational cases with different typical localised failure patterns were successfully examined by quantitatively measuring the inclination angle and thickness of shear band, as well as the microscopic quantities.FindingsThe results show that the shear band formation is stress-dependent, transiting from conjugated double shear bands to single shear band with confining stress increasing. The shear band evolution of two typical localised failure modes exhibits opposite trends with increasing strain level, both in inclination angle and thickness. Shear band featured a larger volumetric dilatancy and a lower coordination number than the surrounding. The shear band also significantly disturbs the induced anisotropy of soil.Originality/valueThis paper proposed an approach to quantitatively assess shear band evolution based on the result of two-dimensional DEM modelling.