Rattlers’ involvement for possibly looser critical states under higher mean stress

Sacha Duverger,Pierre Philippe,Stéphane Bonelli,Jérôme Duriez,M.A Aguirre,L.A Pugnaloni,R Soto,S Luding

doi:10.1051/epjconf/202124911002

Abstract

The critical state of a granular material made of rounded tetrahedral particles is studied through DEM simulations of triaxial compressions. A minimum number of 7,500 particles is first obtained as the representative volume element (RVE) for the present triaxial simulations. Then, the macroscopic critical state line (CSL) is shown to be increasing in the (stress, density) space for low confining pressures. Such an unexpected behaviour is explained by the existence of a significant proportion of rattlers. Considering rattlers as voids indeed reinstates a classically decreasing CSL.

Highlights

The ability of granular materials to sustain increasing shear strains under constant volume and constant shear stress has long been recognised as one of their salient features
Experiments [3,4,5] have shown that a critical state line (CSL) exists in the (log(p), e) plane and that this CSL is decreasing
Tetrahedral particle made of clumped spheres that the slope of the CSL depends on the inter-particle friction angle, and a positive slope was observed therein in some cases

Summary

Material

The ability of granular materials to sustain increasing shear strains under constant volume and constant shear stress has long been recognised as one of their salient features. Experiments [3,4,5] have shown that a critical state line (CSL) exists in the (log(p), e) plane (with p the mean pressure and e the void ratio) and that this CSL is decreasing These observations were mostly confirmed numerically in [6,7,8], using Discrete Element Methods (DEM) with spherical particles and the Hertz-Mindlin contact model. Tetrahedral particle made of clumped spheres that the slope of the CSL depends on the inter-particle friction angle, and a positive slope was observed therein in some cases. Our numerical triaxial tests are performed on a material made of tetrahedral particles interacting according to a visco-elastic contact model with friction. As for the tangential stiffness Kt, it was determined by setting arbitrarily the stiffness ratio Kt/Kn

Contact model

Triaxial tests

RVE determination

Critical state and rattlers’ influence

Conclusion