Variation of the thermal conductivity of a silty clay during a freezing-thawing process

The thermal conductivity of soils is a key factor in calculating soil heat transfer and analyzing temperature fields of geotechnical engineering in cold regions. We measured the thermal conductivity of a silty clay by a QuickLine-30 Thermal Properties Analyzer during a freezing-thawing process, and analyzed the variation of the thermal conductivity. We then calculated the thermal conductivity under the same experimental conditions using the three general models, i.e. weighted arithmetic mean model, weighted harmonic mean model, and weighted geometric mean model. The results show that for the thawed or frozen soils with little variation of unfrozen water content, the thermal conductivity is slightly influenced by temperature; however, for the soils in the major phase transition zone, the variation of the thermal conductivity with temperature is significant. After a freezing-thawing process, the thermal conductivities of the soils with higher initial dry densities become smaller, while those with lower initial dry densities become larger. We also found that the variation of porosity and hysteresis effect of unfrozen water content cause the difference of the thermal conductivity of soils between freezing and thawing processes, however the variation of porosity acts as the primary role. Furthermore, the three general models can all be used to calculate the thermal conductivity of soils; however, the weighted geometric mean model agrees best with the experimental data.