Force transmission in dry and wet granular media

We compare the probability density functions of normal forces in dry and wet granular systems from 3D simulations by molecular dynamics and contact dynamics methods. While the strong forces are characterized by a decreasing exponential distribution, we show that in the range of weak forces the force distribution in a dry granular packing is sensitive to the anisotropy of the packing and the shape of the particles. By means of a model of capillary cohesion, implemented as a force law expressing the capillary force as a function of water volume and the distance between particles, we find that distributions are exponential for both compressive and tensile forces. The particle pressures are shown to form a bi-percolating structure.