A soil's grain-size distribution affects its physical and hydraulic properties; however, little is known about its effect on soil thermal properties. To better understand how grain-size distribution affects soil thermal properties, specifically the effective thermal conductivity, a set of laboratory experiments was performed using binary mixtures of two uniform sands tightly packed with seven different mixing fractions over the full range of saturation. For each binary mixture, the effective thermal conductivity, l, capillary pressure, h c , and volumetric water content, q, were measured. Results demonstrated that the l-q relationship exhibited distinct characteristics based on the percentage of fine-and coarse-grained sands. We further compared measured l-q properties with independent estimates from two semi-empirical models (Campbell Model and Lu and Dong Model) to evaluate the models' applicability in relation to physically based parameters associated with changes in soil mixing (e.g., porosity and grain size). Both models were able to fit experimental data but to varying degrees based on the number of physically based parameters used. In general, model improvements are needed to capture the l-q relationship solely on physically based parameters.Abbreviations: SWRC, soil water retention curve. U nderstanding soil thermal properties is important to properly determine the impact of heat transfer on the distribution, circulation, and evaporation of water in soil. Heat transfer within soil influences micrometeorological phenomena (Hanks et al., 1967), engineering efforts such as cooling electronic devices with heat pipes and insulating buildings (Bussing and Bart, 1997;Sakaguchi et al., 2009;Moradi et al., 2015), agricultural production (Al Nakshabandi and Kohnke, 1965;Usowicz et al., 1996;Lipiec et al., 2007), and landmine detection efforts that rely on thermal contrast (e.g., Garcia-Padron et al., 2002;Martínez et al., 2004). Previous studies provide insight into the effect of soil moisture, temperature, and soil physical characteristics on soil thermal properties, specifically the effective thermal conductivity, l (W m -1 K -1 ; e.g., De Vries, 1963;Johansen, 1975;Hopmans and Dane, 1986;Ochsner et al., 2001;Tarnawski and Gori, 2002). However, to our knowledge, none of the studies to date has investigated the effect of mixing differently sized particles on controlling the l behavior under varying soil water contents (q, cm 3 cm -3 ). Knowledge of the l-q relationship for differently sized soil fractions is particularly important in many engineering applications such as soil borehole thermal energy storage (SBTES), landfill covers, and engineered material stabilization.Previous research provides strong evidence that l is affected by a wide range of parameters including q (e.g., Philip and de Vries, 1957;De Vries, 1963;Yadav and Saxena, 1977; Core Ideas• Thermal conductivity and water content relationship based upon mixtures are distinct.• Systematic change in particle fine fraction directly affects thermal cond...
at Austin in Environmental Engineering. Most recently, he graduated with his Ph.D. from the Colorado School of Mines in Civil and Environmental Engineering. He teaches Water Resources Planning and Management, Environmental Science, and Environmental Engineering Technologies. Col. Jeffrey A. Starke, United States Military Academy COL (Ret) Jeff Starke served as a Military Intelligence officer with command and staff experiences at the battalion, brigade, joint task force and combatant command levels. His most recent operational experience was as a strategic planning at the United States Central Command in support of Operation Inherent Resolve (actions against ISIS). Academically, COL Starke specializes in environmental engineering with research and teaching interests in drinking water, public health, and microbial-mediated processes to include renewable energy resources. COL Starke taught senior-level design courses in Physical and Chemical Processes, Biological Treatment Processes, and Solid and Hazardous Waste Technologies. COL Starke has published several peer reviewed research articles and has presented his research at national and international conferences. He maintains a focus on the scholarship of teaching and learning in engineering education. COL Starke is a registered Professional Engineer (Delaware), member of several professional associations, and is a member of the National Council of Examiners for Engineers and Surveyors (NCEES).
His work has been focused on engineering education and advancements in the field of environmental engineering. His current research interests are in physicochemical treatment processes with recent applications in drinking water disinfection, lead remediation, sustainable environmental engineering systems, and contaminant transport. Butkus is a Board Certified Environmental Engineer and he is a registered Professional Engineer in the state of Connecticut.
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