Small and large strain dynamic response of unsaturated soils.

摘要

Mechanical response of near-surface unsaturated soils in large-strain environments such as earthquakes, landslides, and debris flows is highly dependent on magnitudes and evolution of capillary forces. While the magnitude of capillary forces under static loading has been studied in detail, dynamic response of unsaturated soils associated with viscous deformation and rupture of interparticle liquid menisci at large strain is not well characterized. This document presents microscale (two particles) and mesoscale studies to be able to describe how formation, sudden breakage, and reconstruction of menisci at large strains affect the mechanical response (i.e., shear strength, stiffness, and deformation) of unsaturated soils.;Micro scale pull-apart tests were conducted to achieve better understanding of how deformation rates and separation distances contribute to capillary force evolution and meniscus rupture between two equally-sized glass spheres. Capillary force evolves non-monotonically in a manner that first increases and then decreases with increasing separation distance and it is dependent on the initial meniscus geometry and wettability of the particles. The rate of capillary force reduction as the displacement progresses and the point of liquid bridge rupture are both functions of meniscus volumes and displacement rates. Micro-scale experimental results suggest that dynamic response of bulk (multiparticle) unsaturated soil systems would depend on processes of drainage and imbibition and provide insight into evolution of stiffness and ductility of unsaturated soils undergoing large-strain deformation.;Mesoscale experimental tests were performed to better understand the unsaturated soil behavior after cyclic events. If unsaturated soils undergo large and rapid strains, the menisci that provide the capillary forces may suddenly break leading to a change in mechanical response (e.g., stiffness suddenly drops due to rapid strain change) and it takes a finite length of time to recover. Experimental results show that the mechanical response of unsaturated soils is highly dependent on rate of loading. That is, the evolution of capillary forces under low net stresses may contribute to the slip-stick behavior observed on slope stability failures.;The results presented in this thesis hint at phenomena that should be considered in the modelling of the macro-scale behavior of unsaturated soils. The effect of capillary force evolution, the rupture of the menisci, and the reformation of the water bridges must be considered to properly address the stress-strain behavior of unsaturated soils to capture the behavior of complex, yet ubiquitous material.