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Frost Heave and Thawing Settlement of Frozen Soils around Concrete Piles: A Laboratory Model Test

The frost heave and thawing settlement of soils around piles could cause a series of problems, such as freezing of the pile and reduced bearing capacity of the pile. Based on the soil profiles recorded at a permafrost region in Western China, laboratory tests were performed to investigate the frost heave and thawing settlement of frozen soils around piles. The ambient temperature was adjusted in such way that the thawing and freezing of soils occurred from top to bottom, respectively. As the thawing and freezing reached different depths, the temperature, unfrozen water content, and displacements of soils around eight piles were recorded. The results showed that when the thawing was completed, the unfrozen water content of soil located at a distance equal to the pile’s diameter measured from its face was larger than that of the soil located at a distance equal to triple the pile diameters. At the end of freezing, the unfrozen water content of the soil located at a distance equal to the pile’s diameter (from the pile’s face) was smaller than that of the soil located farther (triple pile diameters). It was also shown that for the soil region between 1 and 2 times the pile diameters from its face, the amount of thawing settlement and frost heave increases, while the magnitude of the soil thawing settlement and frost heave decreases from 2 to 3 times the pile diameters. The laboratory results also showed that the difference in the frost heave and thawing settlement is related to the difference of the performance of heat transfer between the pile and soil during the freezing process. Therefore, a transverse temperature gradient exists in the pile-soil system, causing the unfrozen water to migrate toward the pile–soil interface and freeze.