The influence of particles’ aspect ratio on the shear behaviour of granular materials

Abstract

The mechanical response of granular material depends both on the material properties (e.g. stiffness, anisotropy, permeability, etc.) and particle geometry (shape, roughness, etc.). This paper presents a study of the effect of particle shape (i.e. aspect ratio) on the mechanical behaviour of a granular assembly using DEM (discrete element method). In this study, the numerical simulations employ samples with different particle aspect ratios but identical particle size distribution (PSD). Conventional triaxial compression DEM simulations are carried out under both ‘drained’ and ‘undrained’ (constant volume) conditions. The shear behaviour of the assemblies and the evolution of their microstructure under shearing are examined in detail. At the macroscopic level, the test results show that the particle aspect ratio has a significant effect on the stress-strain curve, peak strength, dilatancy characteristics and critical state behaviour. In particular, the samples with lower aspect ratios can lead to higher peak/residual shear strengths, and higher angles of shearing resistance. The critical state occurs at a higher position in a void ratio versus mean normal stress plot for lowest particle aspect ratio. The results from numerical analysis compare reasonably well with the available experimental data. At the microscopic level, the fabric evolution is greatly affected by the aspect ratio, and the critical state fabric is also examined.