Thermal Conductivity Function for Fine-Grained Unsaturated Soils Linked with Water Retention by Capillarity and Adsorption

A thermal conductivity function (TCF) is proposed for unsaturated fine-grained soils describing the evolution of thermal conductivity with respect to degree of saturation at room temperature and having parameters associated with the different mechanisms of water retention. Calibration with data from different fine-grained soils reveals that the proposed TCF captures the sigmoidal evolution in thermal conductivity with degree of saturation with a better fit to data in the low and high saturation regimes compared to other TCFs. Correlations between the parameters of the proposed TCF with those of a soil-water retention curve (SWRC) that considers both capillarity and adsorption water retention mechanisms confirm the coupling between these thermo-hydraulic relationships. Thermal conductivity values at degrees of saturation of 1 and 0 can be obtained from experiments on saturated and dry specimens, and the parameters of the new thermal conductivity function correlate linearly with the degree of saturation at maximum adsorption and the SWRC pore size distribution parameter. A strong correlation was also observed between maximum suction and thermal conductivity in dry conditions, possibly due to effects of mineralogy and dry density on these parameters. A successful validation example for compacted bentonite indicates that consideration of the mechanisms of water retention permits deeper insight into linkages between the TCF and SWRC for fine-grained soils.