Capillary forces between equally sized moving glass beads: an experimental study

Abstract

The mechanical response of near-surface unsaturated soils in large-strain environments such as earthquakes, landslides or debris flows is highly dependent on capillary forces. While the evolution of capillary forces under static loading has been studied in detail, the dynamic response of unsaturated soils associated with the viscous deformation and rupture of interparticle liquid menisci at large strains is not as well characterized. Particle-scale pullout tests were conducted to achieve better understanding of how separation rates and distances contribute to capillary force evolution and meniscus rupture between two equally sized glass spheres. Capillary forces evolve nonmonotonically in a manner that first increases and then decreases with increasing separation distances and is dependent on the initial meniscus geometry and wettability of the particles. The rate of capillary force reduction and particle separation distance at liquid bridge rupture are functions of the meniscus volume and rate of particle separation. The two-particle experimental results suggest that the dynamic response of bulk (multi-particle) unsaturated soil systems would depend on processes of drainage and imbibition and provide insight into the evolution of stiffness and the ductility of unsaturated soils undergoing large-strain deformations.