Cooperative length approach for granular media

We analyze the non-equilibrium relaxation properties of granular materials in the perspective of a cooperative length approach of Adam and Gibbs. The existence of complex geometrical interactions between the grains induces a rough landscape in the structure of the allowable phase space and in the configurational entropy. At their turn these effects induce the need of complex cooperative rearrangements which account for the very slow relaxation dynamics of these systems. On this basis we relate quantitatively the characteristic dynamical properties to quasistatic quantities, e.g. free-volume and configurational entropy.