This project seeks to advance a pore-scale micromechanical modeling framework for quantifying capillary-induced intergranular stress in unsaturated soils. Focus is placed on refining a statistical upscaling methodology used to differentiate portions of the pore network partially filled with water in the form of interparticle liquid bridges and portions of the pore network completely filled with water in the form of saturated pockets. A corresponding capillary stress function may be computed from relatively simple measurements of the soil-water characteristic curve, quantified over the complete range of pore water saturation, and cast into conventional effective stress formulations for saturated soil behavior. Specific objectives are to refine the modeling framework for capturing generalized pore geometries, account for surface adsorption effects in fine-grained materials, and account for wetting-drying hysteresis effects. Laboratory measurements of water retention behavior, particle and pore morphology, shear strength, tensile strength, and small-strain dynamic behavior will be used to evaluate the model performance. Education and outreach activities designed to stimulate graduate and undergraduate research, diversity, and more effective implementation of unsaturated soil mechanics into practice are integrated with the research plan. Improved basic understanding of the pore-scale forces and processes that govern unsaturated soil behavior is expected to yield insight into problems in geotechnical engineering practice that may occur under unsaturated soil conditions, including precipitation-induced landsliding, foundation and excavation stability, and the dynamic response of compacted earthworks.
