This paper represents study results of the bearing characteristics and influencing factors of large diameter bored pile under refreezing condition in permafrost region. Principles for designing piles in permafrost on the basis of both ultimate capacity and limiting deformations are first reviewed. To solve problems such as pile cap and bridge pier construction, super structure construction, time limit construction, a field experiment was carried out on both the bearing capacity and deformation characteristic of large diameter bored pile in high-temperature fine-granular frozen soil of Fenghuoshan region of the Qinghai-Tibet plateau. Based on ground temperature and in-situ experiment data, pile tip resistance accounted for the entire load is just 2.5% when load on pile top reached 6000 kN after frozen soil refreezing was completed. In the meantime, it was also observed that the deformation features of refreezing large diameter bored pile in permafrost. The bored pile is a typical friction pile of the friction pile characterized by the settlement characteristic that pile tip resistance had less loading sharing ratio. The results also indicated that it was very difficult for the permafrost to refreeze to the original state as soon as it had been disturbed due to the bored pile construction. Also, pile shaft force and pile side resistance were connected to pile top loading, characteristic of frozen soil around the pile and ground temperature. The study results can be used as some guides and references in the process of pile foundation construction.
Key words: bored pile, permafrost, pile side resistance, pile bearing capacity
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