Research PaperA novel refrigerant system to reduce refreezing time of cast-in-place pile foundation in permafrost regions

- The freezeback time of cast-in-place pile foundation was analysed by observed data.
- The concrete strength development of pile foundation was investigated by test.
- The cast-in-place pile foundation with CARS was put forward.
- The CARS may decrease the freezeback time by a year.

The heat of hydration of cast-in-place pile foundations may cause an increase of ground temperature and lower the bearing capacity of pile foundation. Observed temperature data indicated that the cast-in-place pile foundation of the Chalaping Bridge, Qinghai-Tibet Plateau, without any cooling measure required two years to freezeback to a natural state. A cold air refrigerant system (CARS) is proposed to reduce the refreezing time. The CARS operates in winter, and the exhaust fan forces circulation of cold air in the pile foundation and removes heat from the ground. Experimental data indicated the concrete strength of pile foundation met the design criteria after curing 99 days under cold conditions. Based on the experimental result, the operation time of CARS can be established. A three-dimensional FEM model of the cast-in-place pile foundation of Chalaping Bridge with CARS was developed and the cooling effect of CARS was evaluated. The results showed that CARS might decrease the freezeback time by one year.