Impact of subsurface warming on the capacity of helical piles installed in permafrost layers

This paper focuses on the effect of frozen soil thawing on the pull-out capacity of a helical pile in fine-grained soils. Helical piles are increasingly popular in cold regions because of their ease of installation and minimization of the impact of frost heave. However, any temperature changes caused by a warming subsurface may adversely affect pile capacity. In this paper, helical piles installed in frozen soil layers are investigated to elucidate the changes in capacity due to thawing. A numerical model describing the load-displacement and capacity response of helical piles in frozen and thawed soils is successfully validated by comparison to previous results from two field-scale pull-out (tension) experiments. The results indicate that the pile uplift capacity decreases significantly with soil thawing due to decreases in soil undrained strength and stiffness, resulting from increasing pore pressures. The results from this study will contribute towards future development of design guidelines for helical piles in cold regions for sustainable infrastructure and resilient communities.