Slow dynamics of consolidated granular systems: Multi-scale relaxation

Dynamic acousto-elastic testing, a pump-probe scheme, is employed to investigate the recovery of consolidated granular media systems from the non-equilibrium steady state established by a pump strain field. This measurement scheme makes it possible to follow the recovery from the non-equilibrium steady state over many orders of magnitude in time. The recovery is described with a relaxation time spectrum that is found to be independent of the amplitude of the non-equilibrium steady state (pump amplitude) and of the environment in which samples reside. The non-equilibrium steady state and its slow recovery are the laboratory realization of phenomena that are found in many physical systems of practical importance.