Analysis of freezeback process of a thermal pile in permafrost region

The cast-in-place pile foundation is commonly used in construction projects in permafrost regions due to its superior bearing capacity and its effectiveness in reducing the impact of seasonal frost heaving and thaw settlement deformation on structure engineering. The capacity of a cast-in-place pile foundation buried in permafrost is influenced by temperature, increasing as the ground temperature decreases. However, the heat generated during hydration can lead to thawing of the surrounding permafrost, which is a significant drawback. The freezeback process for cast-in-place pile foundations is lengthy, leading to construction delays. To address this issue, a thermal pile was utilized to expedite freezeback and shorten construction time. Experimental results demonstrated that the thermal pile effectively operated under negative air temperatures and minimized the impact of hydration heat on the surrounding permafrost. By the end of the first cold season following construction, the average temperature on the side of the thermal pile had dropped by 0.78 °C compared to its initial state before hydration heat generation. Additionally, the thermal pile enhanced the refreezing and cooling processes by effectively regulating heat during the first cold season after concrete pouring. It shortened the freezing phase duration to about 23 % of that required by traditional methods and reduced the total freezeback time by 32 %. Additionally, it is recommended to complete construction of cast-in-place pile foundations during the warm season to ensure optimal curing temperatures. These findings will be valuable for the design and construction of cast-in-place pile foundations in permafrost regions.