Short-term axial loading of continuous-flight pile segment in frozen soil

Research on the performance of continuous-flight piles for the use in permafrost is rare. In the present laboratory research, continuous-flight pile segments with 89 mm diameter and 300 mm length were installed in frozen soils and loaded under a constant displacement rate. The objectives were to investigate the load-transfer mechanism and the failure modes associated with the shaft resistance of the piles. Pile segments were screwed into a chamber filled with frozen soil and then loaded in the axial direction; installation torques and pile load resistance were measured, respectively, during the installation and loading stages. The effects of soil temperature, salinity, and water content on the short-term performance of these piles were examined. Results show that the pile capacities decreased with warming temperatures. The installation torque increased significantly as the soil temperature and salinity decreased. Cylindrical shearing mode (CSM) and individual bearing mode (IBM) of pile failure were observed at soil temperatures of -1 and -5 degrees C, respectively. Adfreeze and plate bearing resistance were determined under these failure modes. The global failure surface occurred at the edge of the threads under the CSM, and the shear resistance was increased along this surface. The existence of plate (i.e., flights) bearing resistance under the IBM suggests a potential advantage of continuous-flight piles over conventional smooth piles, because the plate bearing resistance is mobilized during loading.