published_or_final_version / Applied Geosciences / Master / Master of Science

Modeling of the mechanical behavior of geomaterials is a fundamental yet very difficult problem in geotechnical engineering. The difficulty lies in that the engineering behavior of geomaterials is strongly nonlinear and anisotropic, depending on confining pressure, void ratio, stress history, and drainage conditions. A traditional approach to the modeling of geomaterials is to formulate empirical equations to fit experimental data. Generally, this approach is not able to provide physical insights into the diverse responses observed in the soil mechanics laboratories. Another conventional approach is to make use of the classical plasticity theory, established mainly for metals, to develop constitutive models for geomaterials. While this approach is capable of shedding light on the mechanisms involved, it has been recognized that such models may violate the basic laws of physics. The objective of this thesis is to apply a new approach to constructing constitutive models for geomaterials, by making use of thermomechanical principles. The essence of the new approach is that the constitutive behavior of geomaterials can be completely determined once two thermomechanical potentials, i.e. the free energy and dissipation rate functions, are specified. The yield function and flow rule in the classical plasticity theory can be established from the two potentials, and the models so derived satisfy the basic laws of physics automatically. In this thesis, the theoretical framework for constructing thermomechanical models is introduced. Several concepts in relation to plastic work, dissipated and stored energy are discussed. Both the isotropic and anisotropic models are formulated and realized in this framework and the generated predictions are compared with the test data of a series of triaxial compression tests on sand. To address the important density- and pressure-dependent behaviors of sand in the framework, a state-dependent thermomechanical model is developed, by introducing the state parameter into the dissipation rate function such that a unique set of model parameters is able to predict the behaviors of sand for a wide variation of densities and pressures. Finally, a thermomechanical model for predicting the complex unloading and reloading behaviors of sand is developed by modifying the hardening laws, and the performance of this model is investigated. / published_or_final_version / Civil Engineering / Master / Master of Philosophy

In this thesis, a 2D CHebyshev spectral domain decomposition method is developed for simulating the generation and propagation of internal waves over a topography. While the problem of stratified flow over topography is by no means a new one, many aspects of internal wave generation and breaking are still poorly understood. This thesis aims to reproduce certain observed features of internal waves by using a Chebyshev collation method in both spatial directions. The numerical model solves the inviscid, incomprehensible, fully non-linear, non-hydrostatic Boussinesq equations in the vorticity-streamfunction formulation. A number of important features of internal waves over topography are captured with the present model, including the onset of wave-breaking at sub-critical Froude numbers, up to the point of overturning of the pycnoclines. Density contours and wave spectra are presented for different combinations of Froude numbers, stratifications and topographic slope. / by Arjun Jagannathan. / Thesis (M.S.C.S.)--Florida Atlantic University, 2012. / Includes bibliography. / Mode of access: World Wide Web. / System requirements: Adobe Reader.

A numerical investigation was conducted to evaluate the geotechnical safety and slope stability of Municipal Solid Waste (MSW) landfills, considering the effects of geosynthetic reinforcements, biodegradation of the waste, and associated changes in material properties, and extreme wind force simulating hurricane conditions. Three different landfill slopes, 1:1, 1:2, and 1:3 having the height of 122m and width of 2134m, were analyzed using Limit Equilibrium Method (SLOPE/W) and Finite Element Modeling (ANSYS). Techniques developed in this study were used to analyze a case history involving a geogrid reinforced mixed landfill expansion located in Austria. It was found that few years after construction of the landfill, there is a significant decrease in the FS due to biodegradation. Extreme wind loading was also found to cause a substantial loss in the FS. The geosynthetic reinforcement increased the slope stability and approximately compensated for the damaging effects of biodegradation and wind loading. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2016. / FAU Electronic Theses and Dissertations Collection