Application of a concrete thermal pile in cooling the warming permafrost under climate change

Permafrost degradation caused by climate warming is posing a serious threat to the stability of cast-in-place pile foundations in warm permafrost regions. Ambient cold energy can be effectively utilized by two-phase closed thermosyphons (TPCTs) to cool the permafrost. Therefore, we installed TPCTs in a cast-in-place pile foundation to create a unique structure called a thermal pile, which effectively utilizes the TPCTs to regulate ground temperature. And we conducted a case study and numerical simulation to exhibit the cooling performance, and optimize the structure of the thermal pile. The purpose of this study is to promote the application of thermal piles in unstable permafrost regions. Based on the findings, the thermal pile operated for approximately 53% of the entire year and effectively reduced the deep ground temperature at a rate of at least −0.1 °C per year. Additionally, it successfully raised the permafrost table that is 0.35 m shallower than the natural ground level. These characteristics prove highly beneficial in mitigating the adverse effects of permafrost degradation and enhancing infrastructure safety. Expanding the length of the condenser section and the diameter of the TPCT in a suitable manner can effectively enhance the cooling capability of the thermal pile and ensure the long-term mechanical stability of the pile foundation even under climate warming.