Experimental investigation on uplift stability of helical anchors in silty sand under freeze-thaw cycles

At present, the helical anchor has been gradually adopted in electric power projects in cold areas. However, the experimental investigation on its freeze-thaw stability in seasonal frozen soil is limited, especially considering the uplift load simultaneously for transmission line foundation. Therefore, the unidirectional freeze-thaw cycle model tests on the helical anchors in silty sand are carried out to investigate the effects of anchor geometry, top constraint conditions, freeze-thaw cycle times and freezing temperature on the development of frost-jacking displacement. It is concluded that when the helical plate is buried below the frozen depth line, the frost-jacking displacement is basically related to the uplift capacity of the anchor, that is, the anchors with larger uplift capacity in non-frozen soil have relatively small frost-jacking displacement. And when the uplift capacities of both are anchors similar, the anchor with small helix-spacing is more beneficial to resisting frost jacking than that with large spacing. The frost-jacking displacement of the anchors partially recovers after the soil melts for the case of the anchors without top constraint, while the upward displacement of the anchors continues to develop during soil melting process for the case of the anchors subjected to uplift force. The single-helix anchor with large diameter and multi-helix anchor with small spacing have good anti-frost-jacking behavior, and their displacement increments at the end of each freeze and thaw become stable after suffering the third freeze-thaw cycle. In the closed system, the decrease of freezing temperature at the same freezing period will increase the tangential frost-heave force of the anchor rod, which will aggravate the development of the frost-jacking displacement. The study results may provide reference for the design of the helical anchors in seasonal freezing areas.