Macro-microscopical Discrete Element Characteristics of Confined Compression and Wetting Test for Unsaturated Loess

A three-dimensional discrete element simulation analysis is conducted using the particle flow method to explore unsaturated loess's macroscopic and microscopic characteristics under the effects of confined compression and rapid wetting. A soft cementation model accounts for the chemical cementation between particles, and inter-particle van der Waals and capillary forces are introduced. The study focuses on the variations in microscopic parameters by selecting suitable contact model parameters. The results showed that the soft cementation contact model accurately reproduces the mechanical properties of unsaturated loess during lateral compression and rapid humidification tests; the micromechanical coordination number increases with an increase in vertical pressure, whereas the inter-particle contact force and contact moment gradually decreases with an increase in water content. However, saturated specimens exhibited an inverse increase. In addition, the proportion of the damage state contact between particles increases with vertical pressure. As vertical pressure gradually grows, strain energy, sliding energy, and damping energy also rise, with strain energy significantly exceeding both sliding and damping energy values. The growth rate of strain energy accelerates with an increase in vertical pressure, peaking at approximately 200 kPa. In addition, strain energy grows gradually with an increase in vertical pressure until it reaches a maximum of around 200 kPa; higher water content correlates with lower final values of strain energy, while the final values of sliding energy and damping energy fluctuate within a small range.