A Temperature-Dependent Model for Thermal Conductivity Function of Unsaturated Soils

The thermal conductivity of soil is an important property in the study of several emerging geotechnical and geoenvironmental engineering applications. In this study, a temperature-dependent model for the thermal conductivity function (TCF) of unsaturated soils is established by considering the effects of temperature on pore structure, water content, and heat transfer mechanisms. Most of the existing TCF models ignore the effects of temperature on pore structure and water content by treating the thermal conductivity only as a function of temperature and isothermal degree of saturation. To address these limitations, a new TCF model is developed by considering the effects of temperature on matric suction and the soil water retention curve (SWRC). The formulation for matric suction accounts for the effects of temperature on the surface tension, contact angle, adsorption, and enthalpy of immersion per unit area. The proposed model also applies a decay function to the degree of saturation to account for the thermal conductivity function affected by heat transfer phenomena such as conduction and convection of pore water in both liquid and vapor phases and latent heat transfer due to vaporization and condensation. A comparison between the results with experimental data obtained from the literature substantiates the validity of the model. The proposed model is used in a parametric study to examine changes in the thermal conductivity of a clay soil under temperatures ranging from 25 degrees C to 100 degrees C.