Partic. vol. 56 pp. 124-131 (June 2021)
doi: 10.1016/j.partic.2020.11.001
Effect of particle type on the shear behaviour of granular materials
Shunkai Liu^{a}, Zhihong Nie^{a}, Wei Hu^{b,*}, Jian Gong^{a}, Peng Lei^{c}
Highlights
Abstract
In discrete element method (DEM) simulations, multi-sphere (MS) clumped and convex particles are two main particle models that are used to study the mechanical behaviours of granular materials. Of interest is the evaluation of the effect of multiple contacts between clumped particles or single contacts between convex particles on the mechanical behaviours of granular materials. In this context, a series of drained triaxial compression tests were conducted on convex true (CT) ellipsoids and MS ellipsoids with aspect ratios (ARs) ranging from 1.0–2.0. The microscale results indicate that at a given AR, the critical friction angle φ_{c} changes with the particle type, whereas the peak friction angle φ_{p} is nearly independent of the particle type. The anisotropic analysis provides underlying mechanisms of the shear strength evolution from two perspectives. First, the anisotropies of granular materials are essential to shear strength as the deviatoric (q)-to-effective mean (p') stress ratio can be expressed as the sum of the anisotropies, i.e.,q/p' ≈ 0.4a_{c} + 0.4a_{n} + 0.6a_{t} , where a_{c}, a_{n} and a_{t} are the normal contact anisotropy, normal contact force anisotropy and tangential contact force anisotropy, respectively. For all samples, a_{c} and a_{n} underpin the shear strength and are influenced by the particle type. The similar φ_{p} displayed by the CT and MS ellipsoids does not translate to similar a_{n} and a_{c} but similar a_{c}+a_{n} for the two particle types. In addition, owing to their larger a_{c}+a_{n}, the CT ellipsoids have a higher φ_{c} than the MS ellipsoids. Second, there is a satisfactory linear relationship between q/p' and a_{c} within strong and non-sliding (sn) contacts a_{c}^{sn} (i.e., q/p' = ka_{c}^{sn}, where k is the fitting parameter. Accordingly, in the peak state, the subtle difference in shear strength is attributed to the greater a_{c}^{sn} in the CT ellipsoids than in the MS ellipsoids that is counteracted by the smaller k. However, in the critical state, the greater difference in a_{c}^{sn} between the CT and MS ellipsoids is partially offset by the smaller difference in k, causing a higher φ_{c} in the CT ellipsoids than in the MS ellipsoids.
Graphical abstract
Keywords
Multi-sphere clump; Convex true particle; DEM; Particle type; Anisotropy; Shear strength