Unsaturated Particulate Materials—Particle-Level Studies

Analyses and experiments are performed to gain further insight into the behavior of unsaturated particulate materials, with emphasis on the pendular stage. First, interparticle forces are computed based on Laplaceapos;s equation; soil particles are ideally considered spherical or flat to facilitate the identification of the most relevant factors that affect unsaturated soil behavior. Second, the small strain stiffness is continuously measured on specimens subjected to drying, and changes in stiffness are related to changes in interparticle forces; data show important differences with previously published trends based on remolded specimens. Third, microscale experiments are performed to assess the strain at menisci failure in multiple deformation modes; results indicate that the lower the water content, the lower the strain required to eliminate the effects of capillarity, therefore, while capillary forces affect small strain stiffness, they may not contribute to large strain stiffness or strength. Finally the rate of menisci regeneration is studied after a perturbation; stiffness recovery decreases with decreasing water content, and full recovery may not be reached when the degree of saturation is low. Several phenomena associated with the evolution of capillary forces during drying are identified.