Thermal performance and applied evaluation of the pre-bored grouting planted nodular pile in warm frozen soil

The thermal effect of pile foundation in frozen ground is crucial for the formation of its bearing capacity. To break through the problems of strong thermal disturbance and slow formation of bearing capacity in the existing pile foundations. In this paper, a new type of pile named Pre-bored Grouting Planted Nodular (PGPN) was first introduced to the permafrost area, which was a prefabricated composite pile. Its unique structure can reduce the amount of cementitious materials and improve the bearing capacity. To reveal the thermal performance of the PGPN pile to warm permafrost, and compare with that of bored concrete pile, the model experiment and numerical simulation of the pile were conducted in this paper. It was found that: 1) The refreezing time and thermal disturbance radius of the PGPN pile were 270 days and 1.8 m, respectively, which were one-third and half of those of cast-in-place pile. The cemented-soil around the PGPN pile could significantly reduce its hydration heat and reduce the thermal disturbance to frozen ground. 2) Because of the high cement concentration in cementedsoil, the early hydration reaction of the pile was strong, and the temporary high temperature provided a favorable environment for the strength maintenance of cemented-soil in frozen soil. On the contrary, the hydration reaction of bored concrete pile lasted a long time, which intensified the degree of thermal disturbance to permafrost; and 3) Affected by the cooling effect of the atmospheric environment and the self-recovery effect of the lower permafrost, the temperature field of the pile foundation refrozen from the upper and lower ends to the middle. The structure of the frozen soil was changed by hydration heat, making it difficult to return to its initial state. The research results can provide data support for the promotion and application of prefabricated pile foundation in permafrost regions.