A finite element model for coupled deformation-flow analysis of unsaturated soil-structure systems and its validation

In recent years, various forms of finite element formulations and numerical tools have been developed for studying the behavior of unsaturated soils. Among these, TeraDysac, a framework based finite element software developed by Ravichandran and Muraleetharan is found to be an effective tool for analyzing soil-structure interaction in a fully coupled manner. This software consists of two decoupled codes: dysac and udysac. dysac is for the analysis of saturated soil-pile system and udysac is for the analysis of unsaturated soil-pile system. The original udysac code has simplified (reduced formulation) and complete finite element formulations.;In this research, the simplified formulation is improved by incorporating a viscous damping model. The improved simplified formulation seems to predict the unsaturated soil-pile interaction response reasonably well, compared to the simplified formulation. As a major development, a partially reduced finite element formulation for coupled deformation-flow analysis of unsaturated soil-structure systems is developed and implemented in TeraDysac. Soil-Water Characteristic Curve (SWCC), which represents the moisture-suction variation of unsaturated soils, is one of the constitutive models necessary for numerical modeling of unsaturated soil systems. In this research, limitations of commonly used SWCC models such as the Brooks and Corey, van Genuchten, and Fredlund and Xing models are extensively analyzed and limitations/disadvantages are identified. Based on this and also to avoid the identified limitations, two new SWCC models are developed and presented in this dissertation. The capability of the new SWCC models in fitting the measured data of different types of soil is investigated. The comparisons show that the new models are effective and can be used to fit the experimental data well over the entire range of degree of saturation. The numerical stability and the performance of the new models in finite element simulations are investigated by implementing these models within TeraDysac and simulating both static and dynamic problems. These studies showed that the new models are numerically stable and effective in calculating the moisture-suction variation in finite element simulations.;Permeability coefficients of fluids occupying the pore space of unsaturated soils greatly influence the deformation and flow behaviors of unsaturated soils. The permeability coefficient varies with degree of saturation or volumetric water content of the unsaturated soils. The other properties that affect the permeability coefficient are void ratio and particle/pore size distribution. Accurate evaluation of the permeability-degree of saturation or permeability-suction relationship is very important to study the coupled deformation-flow behaviors of unsaturated soils using numerical tools. However, experimental studies of coupled deformation-flow problems such as slope failure after rainfall, and contaminant transport will be time consuming and may require advanced equipments. As a result, experimental studies will not be an effective choice.;The properties which affect the permeability coefficients also affect the soil water characteristic of unsaturated soils. Therefore, soil water characteristic curve models can be effectively used to calculate permeability-degree of saturation or permeability-suction variation. In this research, a simple mathematical equation is developed using the model parameters of S-R SWCC models for determining the permeability-suction variation. The predictive capability of the permeability model is verified by comparing with experimental data of eight different soils found in the literature. This proposed model is capable of predicting the relative permeability of water in unsaturated soil over a wide range of degrees of saturation.;An effective coupled deformation-flow analysis finite element model for unsaturated soils, should consist of the following elements: (1) governing equations and corresponding finite element formulation that represent the physical phenomena of unsaturated soils more closely and capable of calculating deformation-flow characteristics in a fully coupled manner, (2) realistic and accurate constitutive model that represents the stress-strain behavior of unsaturated soil skeleton, (3) soil-water characteristic curve (SWCC) model that represents the moisture-suction relationship in unsaturated soils, and (4) permeability model that represents the flow of fluids in unsaturated soils. (Abstract shortened by UMI.)...