Generalized effective stress in unsaturated granulate by DEM analysis

An extension of the Distinct Element Method (DEM) in corporated with a capillary water (CW) contact model proposed is used to obtain an insight into the effective stress in the unsaturated granulate from the viewpoint of strength. The disappearances of menisci and air bubbles were numerically simulated in the wetting process. DEM biaxial compression and hydric tests showed that: with the description of net stresses, peak strength envelopes move parallel to each other in the direction of increases of peak shear strength nonlinearly with the increase of suction. There appears a unique peak/residual strength line if it is described with generalized effective stress (called GES here). The GES due solely to CW (called GESS here), is a nonlinear function of suction on a wide range of values suction. GESS vs. suction curve appears to be analogous to the water-retention curve, and to be correlated with the particle gradation.