Xuelin Wang

ORCID Identifier(s)

0000-0002-4927-7735

Graduation Semester and Year

2020

Language

English

Document Type

Dissertation

Degree Name

Doctor of Philosophy in Civil Engineering

Department

Civil Engineering

First Advisor

Xinbao Yu

Abstract

Unsaturated soil is an essential consideration for many geotechnical engineering fields, for example, soil bearing capacity, soil lateral earth pressure, slope stability analysis, and seepage-related problems. Thermal-hydro-mechanical (THM) processes govern the behavior of unsaturated soils. Therefore, it is critical to simultaneously measure soil moisture, density, and thermal properties to better study THM processes. A thermo-time-domain reflectometry (thermo-TDR) sensor, a dual-probe for both soil moisture and thermal properties, is improved (based on its previous design) and fully calibrated through various soils at different soil moisture circumstances. Nine different chemical reagents with known dielectric constant were utilized to perform calibration of the dielectric constant. Potassium chloride and sodium chloride solutions of different concentrations were used to implement the calibration of electrical conductivity. The effective sampling area for the thermo-TDR sensor was determined using the COMSOL Multiphysics and MATLAB based on the transverse electromagnetic (TEM) propagation mode. The thermo-TDR sensor tested eight types of sands and clays compacted at different moisture contents. The accuracy and precision of thermal properties measurement were evaluated by comparing and analyzing the measurement results from a KD2 Pro thermal properties analyzer. Validation of temperature effects for dielectric constant and electrical conductivity was performed with sand and distilled water. A modified hanging column device (MHCD) furnished with a lab-built thermo-TDR sensor, a T5x tensiometer, and a KD2 Pro thermal properties analyzer with a TR-1 thermal needle were used to test three sands at the laboratory (24 °C) and environmental chamber (10 °C and 2 °C). The measured data indicate that the hydraulic and thermal properties are functions of the drainage and evaporation processes. The measured results, thermal conductivity dry-out curves (TCDC), and soil-water characteristic curve (SWCC) were determined from the measured results. The effect of sand type and temperature on the TCDC and SWCC curves are evaluated. The validation of the soil-water characteristic curve (SWCC) via the MHCD test method was performed using three SWCC models developed by Brooks and Corey (1964), van Genuchten (1980), and Fredlund and Xing (1994). The fitted curves' performance using the Fredlund and Xing model was better than the other two models (Brooks and Corey and van Genuchten models). Numerical models are developed to model the sand dry-out processes (drainage and evaporating) during the MHCD test. The developed models will help to understand the coupled THM processes of sands.

Keywords

Thermo-TDR sensors, Thermal properties, Hydraulic properties, Unsaturated sands, Soil-water characteristic curves, Thermal conductivity dry-out curves

Disciplines

Civil and Environmental Engineering | Civil Engineering | Engineering

Comments

Degree granted by The University of Texas at Arlington

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