Unsaturated soils from a micro-mechanical perspective
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In this study, we explore the micro-scale behavior of granular soils under unsaturated conditions, with a particular focus on the dynamics induced by wetting and drying cycles. Although the pendular regime has been extensively studied, the funicular and capillary regimes remain less understood and are often inadequately represented in existing models. These limitations motivate the development of a new modeling approach capable of capturing more realistic unsaturated soil conditions, particularly within the funicular regime. To address this, we couple the Lattice Boltzmann Method (LBM), used to simulate capillary bridge dynamics, with the Discrete Element Method (DEM), which captures grain kinematics. This LBM-DEM framework successfully reproduces key features such as the Soil-Water Characteristic Curve (SWCC) and the the evolution mean capillary stress in terms of water content. Our simulations reveal notable hysteresis in both suction and mean capillary stress during wetting and drying, proving the model’s ability to represent unsaturated granular materials across all saturation regimes. These findings underscore the importance of micro-scale interactions in predicting the mechanical response of unsaturated soils, offering valuable insights for engineering applications, including the behavior of earthen dikes subjected to climate change-induced hydraulic cycles.