Calculation for Frost Jacking Resistance of Single Helical Steel Piles in Cohesive Soils

摘要

Helical steel piles (HSPs) are currently used as supports for photovoltaic panels in seasonally frozen ground in order to mitigate the adverse impacts of frost jacking; nevertheless, issues frequently arise due to considerable frost-heave forces through the frozen domain and the piles' limited embedment depth. This study aims to properly estimate the heaving of HSPs and the mobilized resisting forces as the frost penetrates, providing a quick guide to the application. To this end, small-scale model tests were first performed on three types of HSPs installed in cohesive soil with a straight-shaft pile served as a comparison. The pile head was vertically constrained or unconstrained when the surrounding soil was to be frozen from the top down. A linear relationship between the anchor-resisting force and pile head displacement was then derived from test data, and its implications for other boundary conditions (e.g., dead load and flexible boundary at pile head) were discussed. A calculation method was finally proposed to analyze the thermomechanical behavior of HSPs during unidirectional freezing process. The applicability of this approach was examined by two indicators. Hopefully, the findings of this paper can be synthesized into design criterion and facilitate a wider use of HSPs.