The effect of soil water and temperature on thermal properties of two soils developed from aeolian sands in South Africa

The influence of soil water content and temperature on the three thermal properties, namely volumetric heat capacity (C), thermal conductivity (Kt) and diffusivity (D) were analysed in laboratory using the KD2 Pro Thermal Analyser. Five water content and temperature levels were investigated in a two-factor factorial experiment. The results showed an interaction effect between water and temperature on all the thermal properties. From the analysis, three important water content and temperature combinations were identified, i.e. wetting of a dry soil with a rising temperature (up to 60 °C), the effect of freezing (0 °C) and thawing (10 °C) with increasing water content, and the excessive wetting of soils beyond 0.16 mm3 mm− 3 with increasing temperature. Wetting of dry soils with little water improved all thermal properties of these aeolian soils. Hence, a 94, 703 and 346% increase in C, Kt and D has been observed between dry and slightly wetted soils. On the other hand, an average 55% decrease in C, 137 and 367% increase in Kt and D, respectively, were observed due to an increase in temperature from 0 to 60 °C in the two water contents. Freezing (0 °C) and thawing (10 °C) temperatures also had a significant influence in the volumetric heat capacity of the soils. As a result, there was an average 8% increase in C as the temperature changed from 0 to 10 °C while a 42% decrease was recorded due to a change in water content from 0 to 0.39 mm3 mm− 3. Though the influence of freezing and thawing temperatures was negligible, Kt decreased by 11% and D increased by 10% due to an increase in water content from 0 to 0.39 mm3 mm− 3. The effect of the excess addition of water with a rising temperature differs for the three thermal properties. Hence, C and Kt increased at a decreasing rate with addition of water up to DUL whereas D increased dramatically with increasing water content up to 0.16 mm3 mm− 3. Throughout all water contents, C increased with temperature. Thermal conductivity and diffusivity also increased with temperature up to DUL and 0.16 mm3 mm− 3, respectively, followed by a decrease with increasing temperature.