Theses and Dissertations

Issuing Body

Mississippi State University

Advisor

Vahedifard, Farshid

Committee Member

Peters, John F.

Committee Member

Stone, Tonya W.

Committee Member

Amirlatifi, Amin

Date of Degree

8-8-2023

Document Type

Dissertation - Open Access

Major

Civil and Environmental Engineering

Degree Name

Doctor of Philosophy (Ph.D)

College

James Worth Bagley College of Engineering

Department

Department of Civil and Environmental Engineering

Abstract

Studying the effects of extreme conditions, such as high temperatures and low humidity, on soil properties is important to various disciplines, including geotechnical engineering, soil science, waste management, crop management, and ceramics. The goal of this research is to investigate the effect of environmental and geometrical factors on microstructure, desiccation cracking, and CO2 flux in clays. The objectives of this research are threefold. (1) Understand the effects of temperature on the microstructure of clay soils; (2) develop a standardized procedure for studying desiccation cracking in a laboratory setting with reliable and repeatable results; and (3) develop an environmental chamber capable of monitoring CO2 flux through a soil sample large enough to accommodate a fully developed crack network. To accomplish these objectives, an array of laboratory testing was conducted. First, this study examines the effects of extreme temperatures on the microstructural properties of clay using FESEM, cation-exchange capacity (CEC) tests, thermal gravimetric analysis (TGA), and Brunauer–Emmett–Teller (BET) surface area analyzer. Second, a standardized procedure for producing accurate and repeatable laboratory tests on the desiccation cracking of soils is presented. The procedure includes specifications for sample collection, material preparation and characterization (including microstructural properties), and the determination of a representative elemental area (REA) for a fully developed crack network. Finally, a new climatic chamber capable of controlling temperature and relative humidity is designed and tested. The chamber can monitor CO2 flux through a fully developed crack network, enabling fundamental research on the relationship between desiccation cracking and the oxidation of soil organic carbon. The key findings indicate a dependency of soil microstructure on temperature changes. CEC and BET surface area significantly decrease with temperatures beyond 100ºC, indicating a relationship that needs further study. Additionally, compacted and slurry cracking behavior was found to be sensitive to boundary geometry and sample thickness. A REA was identified for each slurry sample thickness. The procedures of this research can be repeated for other soil types and used to connect existing and future research to improve understanding of desiccation cracking behavior, and to study the effects of desiccation cracking on other important geo-environmental phenomena.

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