Compaction of granular materials: experiments and contact dynamics simulations

We present an original experimental study of the slow compaction dynamics for two-
dimensional isotropic granular systems. Compaction dynamics is measured at three different
scales : the macroscopic scale through the normalized packing fraction ˜
ρ, the mesoscopic scale
through the normalized fraction ˜
φ of domains ideally ordered in the system, and the microscopic
scale through the grain mobility μ. The domains ideally ordered are found to obey a growth
process dominated by the displacement of domain boundaries. We present also preliminary
results of three-dimensional simulations with a model of contact dynamics. These results allow
to discuss the difference between the two-dimensional and the three-dimensional cases.