Subtleties in discrete-element modelling of wet granular soils

The stress description provided by the discrete-element method when modelling wet granular materials is investigated for the case of low degrees of saturation within the pendular regime. The stress tensor as computed solely from contact and resultant capillary forces between individual pairs of particles is analysed in depth, being compared with an analytically derived stress expression that accounts for the distributed nature of internal actions such as the liquid pressure acting along wetted surfaces. Both fundamentally different approaches are shown to be equivalent, including for low suction values where wetted surfaces are significant and physical internal forces clearly deviate from the resultant point forces considered by the discrete-element method. Under wet conditions, it is demonstrated that the discrete-element entity now includes both a particle and half a meniscus as a unit.