Strength and Fabric Evolution of Unsaturated Granular Materials by 3D DEM Analyses

A three-dimensional (3D) capillary water contact model was established and implemented into the Distinct Element Method (DEM) to investigate the mechanical behavior of unsaturated granular materials. 3D assemblies of spheres were examined under triaxial compression loading with focus on the effects of suction and initial compaction density on macro-behavior (e.g. strength and deformation) and micro-structure (e.g. stress-induced fabric anisotropy). The fabric was described by the directional distribution of contact-normal and transient particle rotation axis. The DEM results show that the cohesion of the material increases with the suction and is independent of the initial compaction density while the peak friction angle only depends on the density. The loading can change the distribution of contacts in a specimen by increasing the proportion of contacts in the loading direction. Particles are statistically more prone to rotate about axes in the plane orthogonal to the loading direction when the specimen is contractive, which is followed by more prominent rotation about the loading direction when the specimen is dilative. The dense assemblies exhibit greater anisotropy than the loose ones for the two defined fabrics.