A fast- freezing system to enhance the freezing force of cast-in-place pile quickly in permafrost regions

Abstract Quick refreezing of the soils surrounding a pile in permafrost regions has been an widely concerned issue for infrastructure construction, since the bearing capacity would be quite small before a full back-freeze was finished. In order to accelerate the refreezing process of cast-in-place pile and improve its freezing force in permafrost, a fast- freezing system (FFS) using the method of artificial freezing was put forward. Field test of two piles with and without FFS was conducted in Beiluhe of the Qinghai-Tibet Plateau (QTP). A three-dimensional thermal-fluid coupling model was established to analyze the cooling effect of FFS under different conditions. The results show that FFS has a significant cooling effect, which can quickly freeze the pile foundation to −3 °C ~ -4 °C, effectively reducing the temperatures of the surrounding soils and increasing the cold reserves of the pile foundation. Even if the molding temperature and the size of the pile increase, it can still reduce the temperature of the pile to below the natural ground temperature. Since FFS significantly reduced the temperature of soils around the foundation and kept the foundation under a lower interface temperature and a higher freezing force for 7 months, the cooling technology can save the latency time of subsequent construction and is meaningful to solve the problem of rapid construction of cast-in-place pile in permafrost.