Model tests on frost jacking behaviors of helical steel piles

The foundations of the photovoltaic frames suffer from uneven frost heave of the soils during cold seasons, triggering generation inefficiency or even the total failure of superstructures. As a result, the helical steel piles (HSP) are widely adopted to deal with frost diseases in engineering practices. A small scale experiment is conducted to assess the jacking behaviors of different helical piles and the piles with no helix exposed to unidirectional freexing. Then, the variation laws of the temperature, jacking displacement and axial uplift force are summarized. The results indicate: (1) The average frost jacking rate η_j is determined as the reasonable index in terms of anti-jacking ability. In this study, η_j of the large half-helix pile is the least, with the value of 1.03 %, and η_j of the multi-helix one is the largest; (2) There is a linear relationship between the jacking displacement and the frost depth, and the layout of helices has impact on the development of frost jacking; (3) With the vertical displacement of the pile restrained, the axial uplift force grows exponentially over the frost depth. Thus, the research results can provide reference to address the frost jacking problems of lightweight structures in seasonally frozen regions.