A Thermal Conductivity Model for Deformable and Unsaturated Soils to Assess the Thermal Behaviour of Energy Piles

This paper presents an empirical model that predicts the thermal conductivity of soils by accounting for the effect of both the degree of saturation and void ratio on the heat exchange capacity of shallow geothermal reservoirs. The model is generated by the product of two terms: the former accounts for the effect of void ratio on the dry thermal conductivity, whereas the latter describes the influence of the degree of saturation on the moisture-dependent thermal conductivity. The model is a function of three parameters, which are easy to calibrate based on their physical meaning. Model predictions are validated against five different sets of experimental data from literature by means of two alternative approaches: blind prediction of thermal conductivity measurements not employed during calibration and numerical simulations of thermal tests performed on energy piles. Results show that the proposed model is capable of accurately predicting both the thermal conductivity of deformable unsaturated soils as well as reproducing the thermal behaviour of energy piles.