Field observation of the thermal disturbance and freezeback processes of cast-in-place pile foundations in warm permafrost regions

The bearing capacity of pile foundations is affected by the temperature of the frozen soil around pile foundations. The construction process and the hydration heat of cast-in-place (CIP) pile foundations affect the thermal stability of permafrost. In this paper, temperature data from inside multiple CIP piles, borehole observations of ground thermal status adjacent to the foundations and local weather stations were monitored in warm permafrost regions to study the thermal influence process of CIP pile foundations. The following conclusions are drawn from the field observation data. (1) The early temperature change process of different CIP piles is different, and the differences gradually diminish over time. (2) The initial concrete temperature is linearly related with the air temperature, net radiation and wind speed within 1 h before the completion of concrete pouring; the contributions of the air temperature, net radiation, and wind speed to the initial concrete temperature are 51.9%, 20.3% and 27.9%, respectively. (3) The outer boundary of the thermal disturbance annulus is approximately 2 m away from the pile center. It took more than 224 days for the soil around the CIP piles to return to the natural permafrost temperature at the study site.