Gang Lei

ORCID Identifier(s)


Graduation Semester and Year




Document Type


Degree Name

Doctor of Philosophy in Civil Engineering


Civil Engineering

First Advisor

Xinbao Yu

Second Advisor

Laureano R Hoyos


ABSTRACT: Unsaturated hydrophobic soils, induced by the decomposition of plant roots or chemical or oil contamination et al., may have potentially negative effects on soil thermal behaviors and further influence the performance of shallowly buried energy systems, including ground heat exchangers, borehole energy geo-storage systems, and buried power cable systems, etc. This research focused on the fundamental understanding of soil thermal behaviors in relation to surface wettability. Surface wettability alteration was conducted in the laboratory by applying dimethyldichlorosilane (DMDCS) on dry sands, which generated a thin hydrophobic layer on the sand particle surface. Several surface characterizations using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and Raman Microscopy, were performed to verify the surface modification. The generated polydimethylsiloxane (PDMS) on the sand surface has been proved to be strong bonding. Laboratory experiments were conducted on two types of quartz sands with various water repellencies using the KD2 standard probe to investigate the effects of level of water repellency, porosity, degree of saturation, and temperature on soil thermal conductivity. The water repellency was found to mitigate soil thermal conductivity by hindering the formation of water bridges at the particle contacts. Nonuniform water distribution within soils was induced, therefore resulting in poor pore fluid connectivity and further generating deficient paths of heat conduction. Based on the experimental results on Ottawa 20/30 and 50/70 sand with various degrees of water repellency, a continuum soil thermal conductivity prediction model was developed. The model overcame the shortcomings of the existing models, accounting for the hydrophobization effect. Validation was performed that the predicted thermal conductivities were found to be in good agreement with experimental data. When estimating thermal conductivity with full range of degree of saturation, the new continuum thermal conductivity prediction model needs parameter calibration.


Water repplent sands, Thermal conductivity modeling, Thermal conductivity


Civil and Environmental Engineering | Civil Engineering | Engineering


Degree granted by The University of Texas at Arlington

Available for download on Friday, August 16, 2024