Quasistatic response of loose cohesive granular materials

Lab Navier, Univ Gustave Eiffel, École des Ponts, CNRS, 14-20 boulevard Newton, 77427 Champs-sur-Marne, France

^* e-mail: walid.lammali@univ-eiffel.fr
^** e-mail: jean-noel.roux@univ-eiffel.fr
^*** e-mail: anh-minh.tang@enpc.fr

Published online: 7 June 2021

Abstract

DEM-simulated model cohesive assemblies of spherical grains of diameter d, with contact tensile strength F₀, once prepared in loose states, are quasistatically subjected to growing isotropic pressure P, and then to triaxial compression, maintaining lateral stresses σ₂ = σ₃ = P while increasing axial stress σ₁ = P + q and strain є₁. Reduced pressure P^* = d²P/F₀ varies from 0.1 (cohesion dominated case, for which systems typically equilibrate with solid fraction Ф ≃ 0.35), to large values for which the cohesionless behavior is retrieved. In triaxial compression, while the moderate strain response (є₁ ~ 0.1) is influenced by initial coordination numbers and mesoscale heterogeneities, the approach to the critical state, as both q (deviator) and Ф steadily increase, gets slower for smaller P^*. Critical ratio q/P strongly increases for decreasing P^*, as roughly predicted in an “effective stress” scheme. Anomalously small elastic moduli are observed in the gel-like structures. While extensive geometric rearrangements take place, no shear banding is observed. Loose cohesive granular assemblies are thus capable of large quasistatic stable plastic strains and ductile rupture.