A numerical study on the thermo-mechanical behaviour of Gothenburg clay

Abstract

The study of thermal piles is one of the new and complex research areas in geotechnical engineering, where the coupled thermo-mechanical behaviour in the soil surrounding the pile needs to be understood, whether in the heating or cooling stage. This thesis focuses on studying a metal pile which is subjected to thermal loading of heating for 21 days and 13 days of cooling. Several variables were investigated during the research, such as the effect of changing the soil thermal properties (i.e., heat capacity, thermal conductivity), and changing the soil mechanical model (i.e., linear elastic, Modified Cam Clay). In addition to the temperature distribution in the soil, the developed excess pore water pressure was also investigated for several values of the volumetric thermal expansion coefficient. These results were compared with the experimental study of an in-situ pile filed in the Utby in Gothenburg (Bergström, 2017). The study shows, on one hand, that the thermal flow calculations yielded a good agreement between the numerical and experimental values where the heat spreads to about 2 m from the pile, then returns to the earth natural temperature of 8.5oC. On the other hand, changing the thermal properties and changing the used soil constitutive model has minor effects on the results. Additionally, the pile mechanical loading did not affect the heat spread if compared to the case of loading free. As for the excess pore water pressure, the selected models for the numerical study could not capture the experimental measurements suggesting that a more advanced soil model is needed to replicate the thermal effects on the excess pore water pressure.