Unsaturated particulate materials - Particle-level studies

Analyses and experiments are performed to gain further insight into the beh avior of unsaturated particulate materials, with emphasis on the pendular s tage. First, interparticle forces are computed based on Laplace's equation; soil particles are ideally considered spherical or flat to facilitate the identification of the most relevant factors that affect unsaturated soil be havior. Second, the small strain stiffness is continuously measured on spec imens subjected to drying, and changes in stiffness are related to changes in interparticle forces; data show important differences with previously pu blished trends based on remolded specimens. Third, microscale experiments a re performed to assess the strain at menisci failure in multiple deformatio n modes; results indicate that the lower the water content, the lower the s train required to eliminate the effects of capillarity, therefore, while ca pillary forces affect small strain stiffness, they may not contribute to la rge strain stiffness or strength. Finally the rate of menisci regeneration is studied after a perturbation; stiffness recovery decreases with decreasi ng water content, and full recovery may not be reached when the degree of s aturation is low. Several phenomena associated with the evolution of capill ary forces during drying are identified.