| This dissertation centers on unsaturated soil stiffness and the post-liquefaction shear strength of sandy soils. The main goals are to explore the effects of unsaturation on shear stiffness, to identify underlying physical processes involved in post-liquefaction shear strength, to recognize inherent limitations in test procedures, and to provide adequate procedures and criteria for the assessment of post-liquefaction shear strength in saturated soils for engineering practice.; The negative pore-water pressure in unsaturated soils adds an additional interparticle force, resulting in the change in stiffness and strength. The behavior of unsaturated soils is related to particle size, shape, and water content. The shear strength of a liquefied soil can be assessed within the framework of critical state soil mechanics, which captures the large strain behavior of soils. Critical state parameters are strongly related to microscale soil properties and are correlated to soil index properties. The critical state parameters can be effectively obtained in the laboratory using the simple CS test procedure. Strain localization affects the determination of critical state parameters. The use of contractive, homogeneous specimens subjected to drained shear is recommended. The void ratio is the most important parameter to estimate the post-liquefaction shear strength. Its spatial distribution affects the macro-scale behavior. The interaction among temporal and spatial scales requires further studies. |
