How particle shape affects the critical state, triggering of instability and dilatancy of granular materials – results from a DEM study

The discrete-element method (DEM) has gained popularity for developing a qualitative understanding of soil behaviour under a critical state soil mechanics (CSSM) framework. Most studies with a three-dimensional assembly of particles have used spheres as representative granular material to reduce computational demands. However, most granular materials – for example, sands – are not rounded, but possess features of angularity. Therefore, ellipsoid and cluster particles with different degrees of eccentricity were used in this study to evaluate the effect of the particle shape on the drained and undrained triaxial loading behaviour after isotropic and K₀ consolidation. The particle numerical properties and grain size distributions were kept the same for all specimens, irrespective of particle shape. The critical state data points for spheres and ellipsoids plotted on almost the same critical state line (CSL) in e–log(p′) space, whereas the CSLs of clusters plotted above them. Additionally, M lines shifted downward with increasing sphericity. It was also found that the stress ratio at the triggering of static liquefaction (η_IS = q/p′) in η_IS–ψ space was affected by particle shape and consolidation path. The dilatancy (d = dε^p_v/dε^p_q) was also affected by particle shape. It was found that dilatancy parameters for the SANISAND constitutive model are affected by particle shape, which may contribute to an improved understanding of particle shape in constitutive modelling.