Résumé
Using Contact Dynamics simulations of quasistatically driven assemblies of rigid particles we show that the contact network at every stage of deformation is composed of two complementary subnetworks: a "strong" percolating subnetwork of the contacts carrying a force larger than the mean force, and a "weak" subnetwork of the. contacts carrying a force lower than the mean force. In the strong subnetwork, all contacts are nonsliding and forces have a decreasing exponential distribution. Almost the whole dissipation takes place inside the weak subnetwodc, where the number of normal forces decays as a power-law. The strong subnetwork supports all the deviatoric load, whereas the weak subnetwork contributes only to the mean pressure. The orientation of the induced anisotropy (major principal axis of the fabric tensor) in the strong subnetwork is the same as that of the stress tensor, but the orientation of the induced anisotropy in the weak subnetwork is orthogonal.