  The propagation of mechanical energy in granular materials has been
intensively studied in recent years given the wide range of fields that have
processes related to this phenomena, from geology to impact mitigation and
protection of buildings and structures. In this paper, we experimentally
explore the effect of an interstitial fluid on the dynamics of the propagation
of a mechanical pulse in a granular packing under controlled confinement
pressure. The experimental results reveal the occurrence of an
elastohydrodynamic mechanism at the scale of the contacts between wet
particles. We describe our results in terms of an effective medium theory,
including the presence of the viscous fluid. Finally, we study the nonlinear
weakening of the granular packing as a function of the amplitude of the pulses.
Our observations demonstrate that the softening of the material can be impeded
by adjusting the viscosity of the interstitial fluid above a threshold at which
the elastohydrodynamic interaction overcomes the elastic repulsion due to the
confinement.
