A general observation is that the influence of polydispersity on mechanical behaviour has been the subject of very few systematic studies in the literature. In the framework of a project with CEA Cadarache on the compaction of Uranium powders, we have shown that the packing fraction increases both with increasing polydispersity in size and shape. However, shape polydispersity dominates at low particle size distributions, while size polydispersity dominates at high particle size distributions. Under quasi-static loading, a remarkable result is that the internal angle of friction is independent of the grain size distribution, but surprisingly it decreases with increasing shape polydispersity. On a microscopic scale this is explained by a greater dispersion of the contacts as the shape irregularity increases. In a second collaboration with CEA-Cadarache we have extended these surprising results to the 3D case of spherical powders. In collaboration with Chiang Mai University we have extended these results to the case of polyhedral grains.

In a completely different application context, in collaboration with the SRK company located in Australia, we were interested in the characterization of coarse mining waste. Such a characterization requires elaborated techniques for modifying the particle size distribution, which leads to difficult reproducibility of results. We have clearly shown that the reproducibility of the results requires to take into account the alteration of the shape of the grains in each sub-grain size class. Such a result should lead to an update of standard geotechnical practices. These studies should be continued, this time considering very polydisperse but cohesive materials (presence of water on contact).

Main articles

6] Microstructural analysis of sheared polydisperse polyhedral grains Phys. Rev. E 2020
5] Impact of grading on steady-state strength, Geotechnique Letters 2019
4] Rheology and structure of polydisperse three-dimensional packings of spheres, Phys. Rev. E 2019
3] Shear strength and microstructure of polydisperse packings: The effect of size span and shape of particle size distribution, Phys. Rev. E 2017
2] Effects of shape and size polydispersity on strength properties of granular materials, Phys. Rev. E 2015
1] Effect of size polydispersity versus particle shape in dense granular media, Phys. Rev. E 2014