Adfreeze Strength of Wooden Piles in Warm Permafrost Soil

In recent years, permafrost warming has adversely affected the performance of infrastructure projects in northern Canada. The common construction practice in these permafrost-underlain areas is to use the pile foundation for building and infrastructure rather than using shallow foundations. Thus, the influence of warming permafrost on the loading capacity of pile foundations is critical for evaluating forthcoming changes under a warming climate. The present study was performed to assess the influence of temperature and loading rate on the adfreeze strength of piles in permafrost soil. A series of uniaxial compressive tests on wooden piles drilled into frozen soil were carried out at various temperatures, mimicking the conditions in warming permafrost. The results demonstrated that an increase in strain rate led to an increase in the adfreeze strength of piles. Moreover, the wooden piles exhibited peak adfreeze strength at a displacement of less than 2 mm for most temperature and deformation rate combinations. Interestingly, although the adfreeze strength of piles increased as temperatures cooled below −1°C, a transition phase between −3°C and −4.5°C was observed in which the adfreeze strength decreased. It could be noted that failure occurred in the wooden piles at temperatures colder than −5°C rather than frozen soil failure at these temperatures. These variations in the adfreeze strength were related to soil temperature, unfrozen water content, and the adhesive bonds at the interface between the frozen soil and pile.