Discrete element simulations of direct shear tests with particle angularity effect

Abstract

This paper investigated the effect of the particle angularity in light of its importance in angular particle assemblies, using the discrete element method (DEM). A discrete element model with a general contact force law for arbitrarily shaped particles was developed, in which angular particles were modeled using convex polyhedra. Quasi-spherical polyhedral shapes with different vertexes were adopted to reflect the change of angularity. Four categories of assemblies with different angularities were generated. A series of direct shear tests performed on these assemblies were simulated at different vertical stresses. All numerical implementations were achieved using a modified version of the open source DEM code YADE. It was found that the macroscopic shear strength and dilatancy characteristics are in agreement with experimental and numerical results in the literature, indicating that the present numerical model is reasonable. Besides, the evolutions of coordination number, normal contact force distribution, and anisotropies of particle orientation and contact normal were investigated. The results show that the angularity plays a vital role in strengthening the interlocking of angular particles.

Geomechanical Modelling of Railroad Ballast: A Review

“…Zaho et al [194] showed the importance of particle angularity in modelling of ballast behaviour. The authors studied the shear stress-strain, volumetric change and the relationship of friction angle and cohesion to angularity.…”

Qualitative and quantitative DEM analysis of cohesive granular material behaviour in FT4 shear tester

“…The values of φ are in the range of 15° to 35° and are expected to be smaller than the experimental measurement because of the effect of particles angularity. In other words, if a geometric parameter for the particle shapes is considered in the DEM simulation, φ is expected to increase (Zhao, et al, 2015). The particles used in the simulation are perfectly spherical, which decreases the value of φ (Coetzee, 2016).…”

Simple particle shapes for DEM simulations of railway ballast: influence of shape descriptors on packing behaviour

“…[21] defines convexity with respect to the particle's volume, while [39] defines it using perimeters of approximating intersections of spherocylinders. Some works even define shape descriptors, which can only be used for the chosen DEM particle type: [63] defines angularity of the polyhedral particles as ratio of the sphericity to the number of vertices. These examples show again the challenge of particle shape characterisation and that care has to be taken when drawing conclusions from different studies.…”