  We propose a simple phenomenological model for wet granular media to take
into account many particle interaction through liquid in the funicular state as
well as two-body cohesive force by a liquid bridge in the pendular state. In
the wet granular media with small liquid content, liquid forms a bridge at each
contact point, which induces 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.
