Characteristics of compressive bearing capacity and resistance to foundation freeze-thaw of the isolation helical pile

Based on the isolation helical pile designed to resist vertical loads and eliminate the effect of foundation freeze-thaw, the pile force evolution, load transfer, and foundation response characteristics of two typical types of helical piles (S/D＜S/Dcr and S/D≥S/Dcr) during settlement, as well as the influences and mechanisms of pile geometries on the bearing capacity of the single pile are revealed from the pile force perspective. Furthermore, the performance of the new pile against foundation freeze-thaw deformation is examined. The results show that: (1) The bottom helixes and the lower pile bodies of the two typical piles share the same stress characteristics during the settlement, whereas the stress magnitude and evolution characteristics of the remaining upper helixes’ end resistances and inter-helixes pile side friction resistances differ significantly. (2) The end resistance of each helix of pile S/D≥S/Dcr is essentially equal, and the additional stress that the helixes exert on the underlying soil significantly enhances the pile side friction. This also determines the top-down near-exponential decay trend of the pile side frictional resistance between the helixes. The upper helixes’ end resistances were only about 1/5 of the bottom one for pile S/D＜S/Dcr. (3) The compressive bearing capacities of the two types of piles all grow linearly as embedment ratio, helix diameter, and helix number increase, while linearly increases first and then decreases rapidly with the increment of shaft pile diameter. These pile geometries possess heavier impacts on the bearing capacity of pile S/D≥S/Dcr. The bearing capacity of pile S/D＜S/Dcr increases significantly with the increase of S/D, whereas that of pile S/D≥S/Dcr decreases linearly. (4) Helical pile has a significant advantage over the conventional pile in resisting the impact of foundation freezing-thawing deformation. The impact can be further eliminated by installing an isolation sleeve on the pile within the frozen soil depth.