Evaluation and Laboratory Measurement of the Coefficient of Permeability in Deformable, Unsaturated Soils

Abstract

The primary objective of this dissertation is to study the coefficient of permeability function for unsaturated soils. The research program commenced with a literature review on the coefficient of permeability function. The permeability function for a constant volume porous medium was categorized into empirical equations, macroscopic models and statistical models. The influence of void ratio on the coefficient of permeability for a saturated soil was outlined as well, followed by a discussion on the permeability function of a deformable, unsaturated porous medium. The limitations of the available models were briefly discussed. On the basis of the available information, a theory which incorporated the influence of both void ratio and degree of saturation has been developed. New models were proposed corresponding to the empirical equations, macroscopic models and statistical models presented in the literature review. The proposed model can be represented by a three-dimensional surface, which is referred to as the coefficient of permeability surface. The influence of Volume change on the permeability function for a selected silty soil was experimentally investigated using a specially designed triaxial permeameter system where the stress state variables (i.e., the net normal stress, (o - ua), and the matric suction, (ua - uw)) were independently controlled. Twelve silt specimens were consolidated either isotropically or one-dimensionally (i.e., K, consolidation), after which measurements of the coefficient of permeability were made at specified matric suctions. The total volume changes during the tests for the isotropically consolidated specimens were continuously monitored using three non-contacting strain indicators. The specimens were consolidated to various void ratios under different consolidation pressures. Another twelve specimens were placed in a pressure plate cell in order to define the soil-water characteristic behavior for the drying process starting at different initial void ratios. The experimental data, along with available data for swelling soils in the literature, were analyzed and discussed as it relates to the proposed theory. The analyses showed that the theory can be used to describe the coefficient of permeability of an unsaturated soil. The soil-water characteristic behavior was found to be of value in the prediction of the permeability function for unsaturated soils.