Self-organization, localization of shear bands, and aging in loose granular materials

We introduce a mesoscopic model for the formation and evolution of shear ba nds in loose granular media. Numerical simulations reveal that the system u ndergoes a nontrivial self-organization process which is governed by the mo tion of the shear band and the consequent restructuring of the material alo ng it. High density regions are built up, progressively confining the shear bands in localized regions. This results in an inhomogeneous aging of the material with a very slow increase in the mean density, displaying an unusu al glassylike system-size dependence.