Spatio-temporal variability on the interface thermal resistance of clay-sand composite strata

Thermal contact resistance (TCR) at the interfaces of soil layers has significant effect on thermal conductivity of composite strata. However, limited investigation has been conducted in this subject. A model test of a clay-sand composite stratum heated at the clay end is established. TCR tests are conducted at temperature gradients of 50 °C, 60 °C, 70 °C, and 80 °C using a self-made soil column thermal resistance tester, revealing that TCR increased with rising temperature. Subsequently, a large-scale rectangular plate heating model tester is employed to measure TCR in layered soil. The results show that, temporally, TCR initially increases rapidly, then gradually decreases, and eventually fluctuates within a certain range. Spatially, TCR increased with increasing distance from the heating center and is lower along the shorter side of the rectangular heating zone compared to the longer side. Finally, finite element numerical simulations are performed to model the temperature fields in the one-dimensional soil column and the clay-sand composite stratum, considering the spatial distribution of TCR. The simulation results are in good agreement with two experiments. This study provides valuable insights for optimizing economic and thermal performance in geotechnical engineering involving heat conduction, emphasizing the importance of balancing energy supply and heat loss.