Simple model for wet granular materials with liquid clusters

We propose a simple phenomenological model for wet granular media to take into account the many-particle interaction through the liquid in the funicular state as well as the two-body cohesive force by a liquid bridge in the pendular state. In the wet granular media with small liquid content, the liquid forms a bridge at each contact point, which induces a two-body cohesive force due to the surface tension. As the liquid content increases, some liquid bridges merge, and more than two grains interact through a single liquid cluster. In our model, the cohesive force acts between the grains connected by a liquid-gas interface. As the liquid content increases, the number of grains that interact through the liquid increases, but the liquid-gas interface may decrease when liquid clusters are formed. Due to this competition, our model shows that the shear stress has a maximum as a function of the liquid content.