Abstract

Due to the dynamic nature of the shallow subsurface, knowledge of soil thermal properties across a wide range of soil moisture and temperature conditions is necessary to accurately describe heat transport in many settings. Soil thermal properties are difficult to measure at high temperatures, however, due to the lack of suitable measurement devices and the potential for measurement-induced changes. Therefore, thermal property data are often scarce and incomplete and very often limited to specific soils. Due to this scarcity of accurate experimental data, empirical relationships often do not accurately predict the thermal properties of soils as a function of both soil moisture and temperature. In this study, thermal conductivity and diffusivity were measured for silica sands under loose and tight packing conditions and a field sand under varied water saturation and temperature. Several recent sensor-based technologies were integrated into a small cell modified to have a network of sampling ports, continuously monitoring water saturation, temperature, and soil thermal properties. For the test sands studied, data showed that the thermal conductivity and diffusivity increased noticeably for sample temperatures >50°C. At sample temperatures between 30 and 50°C, any change in thermal properties with temperature was small. Thermal conductivities measured in this study were compared with independent estimates made using empirical models from the literature. In general, good agreement was observed for most thermal conductivity data when proper fitting parameters were established, except at intermediate saturation values.

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