Date of Award

Winter 2017

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Materials and Infrastructure Systems

First Advisor

Jay Wang

Abstract

Moisture content in soil has a great implication in engineering design, and it has been heavily investigated by soil engineers and scientists. If moisture content in expansive soil changes drastically, it will create significant volume change in the soil. If expansive soil is present in building foundation or pavement subgrade, it may result in structural failure. On the other hand, if sufficient moisture content is present in soil, it will increase the production of geothermal energy from the ground soil. This dissertation is an effort to understand the effects of moisture content on both expansive soils and geothermal energy that is extracted from ground soils.

Louisiana has been affected by its expansive soil. In north Louisiana especially, pavements often get longitudinal cracks due to the expansive subgrade soil. In this dissertation, one of the major types of expansive soils, which is called Moreland clay, is investigated to understand the swell-shrink properties. The dissertation research started with the characterization of Moreland clay by performing a series of laboratory tests. As a by-product, a GIS-based swelling potential map of expansive soil in Louisiana was developed. It is concluded from the characterization that Moreland clay is one of the most expansive soils in the world.

In the dissertation research, an easily implementable model is developed based on the theory of beam on elastic foundation, in which the mechanism of soil strength is mathematically considered. The predicted heave or shrinkage of expansive soils below the pavement is integrated in the model as the beam deflection. In the proposed method, pavement is simplified as a beam with a virtual load as a form of Fourier series applied on top of the beam to mimic the heave/settlement caused by the volume change of expansive soils. The virtual load is determined by making the predicted subgrade soil heave/settlement equal to the beam deflection. Finally, a closed-form solution of the beam's deflection, rotation, bending moment and shear force are developed, which is caused by the heave/shrinkage of the expansive soil below the pavement. Compared with the traditional finite element models, the proposed analytical model is significantly more simple and more easily implemented. The closed-form solutions make pavement stress analyses and soil heave predictions separate. All the equations and calculations are incorporated in the Excel spreadsheet. The Excel-based software package will be the only required tool for design calculations. As a part of the expansive soil research, using different soil stabilizers (e.g., geopolymer concrete (GPC) and cement) to stabilize the expansive soil is also investigated.

Finally, the moisture content of soil on geothermal energy is investigated. At the beginning, a three-story building in New Orleans is designed with an energy-pile foundation as an example to see the prospect of geothermal energy in Louisiana. The research shows, if geothermal energy is used for the building's heating and cooling energy source, less carbon dioxide would be emitted compared to its traditional heating and cooling energy source (i.e., electricity, natural gas, etc.). As a part of the research, a simple graph method is proposed to design a borehole heat exchanger for small apartments and offices. A small apartment in Ruston, Louisiana, is designed as an example using the graph method and later again designed with the two very popular commercial software GLD 2012 and GLHEPRO. The result from the graph method shows a great convergence with both commercial software programs. At the end, a sensitivity analysis of different design parameters of energy pile is performed to have a better understanding of the geothermal energy system.

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