ABSTRACT
In this paper, we propose to study experimentally internal rearrangements in a weakly perturbed granular material through electrical conductivity measurements. Small thermal perturbations lead to giant intermittent fluctuations of conductance gathered in bursts. The burst structure has been characterized via a statistical analysis of the waiting time At between two peaks of fluctuations. Both local and collective contributions have been isolated. The local part corresponds to individual beads creep. Its electrical signature is a power law distribution on At with an exponent related to the roughness exponent of the beads surface. The collective part is related to wall effect rather than collective vault reoganisations. Electrical response of the packing to several successive heating-cooling cycles also shows that, although thermal perturbations are insufficient to change the beads network, thermal ‘compaction’ can be observed in the sense that heating-cooling perturbations have less and less effect on the packing resistance.
