Sam Edwards more than 30 years ago proposed a model to describe the statistics of granular packings by an ensemble of equiprobable jammed states. Experimental tests of this model remained scarce so far. We introduce a simple system to analyse statistical properties of jammed granular ensembles to test Edwards' theory [1]. Identical spheres packed in a nearly two-dimensional geometrical confinement were studied in experiments and numerical simulations. When tapped, it evolves towards a ground state, but due to incompatible domain structures it gets trapped. Analytical calculations reproduce relatively well our simulation results, which allows us to test Edwards' theory on a coupled system of two subsystems with different properties. We find that the joint system can only be described by a common compactivity if the stress equilibrium is also taken into account. The results show some counterintuitive effects, as the side with less free volume compactifies.

 

[1]: S. Levay et al,  arXiv:2007.04789