Experimental study of solid-liquid-type transitions in vibrated granular layers and the relation with surface waves

From pressure and surface dilation measurements, we show that a solid-liquid-type transition occurs at low excitation frequencies in vertically vibrated granular layers. This transition precedes subharmonic bifurcations from flat surface to standing wave patterns, indicating that these waves are in fact associated with the fluidlike behavior of the layer. At higher frequencies we show that another kind of subharmonic waves can be distinguished. These waves do not involve any lateral transfer of grains within the layer, and correspond to excitations for which the layer slightly bends alternately in time and space. These bending waves have very low amplitude, and we observe them in a vibrated two-dimensional layer of photoelastic particles.