Estimating the thermal conductivity of granular soils based on a simplified homogenization method

Thermal conductivity is a fundamental parameter for analyzing the thermodynamic behavior of granular soil as well as the workability of geothermal structures. Most of the previous work on modeling the thermal conductivity of granular soil is empirical, and the inter-granular structure is not considered. Therefore, a simple yet effective model is required for accurately capturing the heat transformation behavior of granular soils. To this end, a structure variable is introduced to describe the evolution of inter-granular structure of granular soils, which is found to decrease with the porosity but is rather independent of the nature of particles. Based on the insight drawn from the laboratory tests, a simple homogenization equation is formulated for correlating effective thermal conductivity of granular soil and that of soil particles. Finally, a novel thermal conductivity model is established by incorporating the structural variable into the simplified homogenization equation. Validation of the model is done by comparing the predicted results with the experimental data as well as the data compiled from literatures, indicating that our model can effectively capture the thermal conductivity of various granular soils with wide range of porosity.