Assessment of thermal conductivity of unsaturated frozen soils based on three-dimensional numerical models

The thermal conductivity of unsaturated frozen soil is a critical parameter influencing a wide range of engineering applications, including geothermal energy systems, radioactive waste disposal, and infrastructure development in cold regions. As a typical multiphase medium comprising solid, gas, ice, and water, the thermal behavior of unsaturated frozen soil is highly complex, with each constituent phase affecting the overall thermal conductivity. This complexity poses significant challenges for accurate prediction. To address this issue, a novel three-dimensional (3D) identification-reconstruction-mesoscale-simulation model is proposed to evaluate the thermal conductivity of unsaturated frozen soils. The modeling process consists of three key steps: feature identification, mesostructure reconstruction, and thermal conductivity calculation. The first step is implemented by computed tomography scanning, contacting angles testing as well as nuclear magnetic resonance to determine the input parameters. Following this, the identified characteristic parameters are utilized to reconstruct mesostructured. Thermal conductivity is then calculated by the finite-element method coupled with the Monte Carlo simulation. To verify the accuracy of the proposed model, numerical data are compared with the results obtained from experiments and empirical models. The comparison demonstrates that the proposed approach offers strong predictive capability for the thermal conductivity of unsaturated frozen soils. Furthermore, a parametric study is conducted using the 3D model to explore the effects of phase composition on thermal conductivity. This study provides new insights into the influence of internal structure on thermal behavior and offers practical guidance for engineering applications in cold regions.