This paper focuses on the thermo-hydro-mechanical behavior of soft clay surrounding a prefabricated thermal drain. A prefabricated thermal drain combines features of a conventional prefabricated vertical drain (PVD) and a closed-loop geothermal heat exchanger by placing plastic tubing within the core of the PVD through which heated fluid can be circulated. The prefabricated thermal drain can be used to increase the temperature of the surrounding soft clay, which will generate excess pore water pressures due to differential thermal expansion of the pore fluid and clay particles. As these excess pore water pressures drain, the soft clay will experience volumetric contraction. The elevated temperature leads to an increase in the hydraulic conductivity and the volumetric contraction leads to an increase in thermal conductivity, making this a highly coupled process. Although thermal drains have been tested in proof of concept field experiments, there are still several variables that need to be better understood. This paper presents numerical simulations of the coupled heat transfer, water flow, and volume change in the soft soil surrounding a prefabricated thermal drain that were validated using the results from large-scale laboratory experiments. Numerical simulations were found to agree well with the experimental data. A further analysis on the performance of the thermal PVD indicates an increase in surface settlement with an increase in drain temperature and a significant reduction in the surcharge required when using a thermal PVD.
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