Multifactorial influence patterns and resistance mechanisms of frost-jacking characteristics in conical piles

To investigate their evolution characteristics of frost-jacking behavior and their resistance mechanisms, a testing device for the anti-frost-jacking performance of conical piles is developed. The unidirectional freezing tests on the conical piles are conducted to analyze the effects of pile materials, cone angles, soil moisture contents around the piles and freeze-thaw cycles on their frost-jacking performance as well as their anti-frost-jacking mechanisms. It is indicated that under the same conditions, the frost-jacking displacement of the piles decreases exponentially with the increase in the cone angles. As the number of freeze-thaw cycles increases, the growth rate of the frost-jacking displacement for vertical piles increases in a semi-logarithmic manner, while changes in the conical piles are not significant. The pile materials have a significant impact on the frost-jacking characteristics of the conical piles, and the wooden pile may experience thawing extraction. During the unidirectional freezing process, the moisture within the soil surrounding the piles migrates upward from the bottom. The greater the initial moisture contents, the more pronounced the migration, leading to larger frost-jacking displacements. However, the effects of the moisture contents on the frost-jacking displacement are weaker than those of the cone angles. During the freezing process of the soil around the piles, the freezing depth increases, the tangential frost-jacking force on the pile surface increases, and the normal frost jacking force gradually decreases from compressive stress to tensile one. When these two forces exceed the tangential freezing strength of the soil and the ultimate normal tensile strength, the frost-jacking of the piles occurs. Considering the resistance to frost jacking, economic factors and the protection of frozen soil, the cone angles of the anti-frost-jacking conical piles should be designed to be between 7° and 9°, but the pile depth must also be taken into account.