Axial performance of screw micropiles subjected to quick loads in frozen soils

Screw micropiles have been recently introduced to North America as a new foundation type. The screw micropile is a steel pipe pile, threaded and tapered along its lower segment. Due to the unique characteristics, screw micropiles have major advantages such as lightweight, large capacities, reusability, and rapid installation. Screw piles may be a viable solution to foundations in the Canadian Arctic where piles are often backfilled with slurry or gravel. Conventional piles used in the Canadian Arctic require time-consuming freeze-back. However, currently there are no guidelines for the use of screw micropiles in permafrost regions. The present research investigated the engineering behaviour of screw micropiles subjected to short-term loading conditions in frozen ground using the Cold Room Facilities at the University of Alberta. Piles were installed into a smaller pilot hole in the frozen soil, which is intended to simulate the field installation method. The effects of temperature and ice content upon the short-term loading performance of model piles were examined. Preliminary results showed that the pile capacities decreased with the increase in soil temperature. The installation torque was recorded and used to infer the torque required for field installation. The failure pattern of the piles was observed to be located along the edge of individual threads; this pattern suggests that the pile capacities may be greater than conventional pipe piles in the Arctic.