Effect of the Addition of a Second Helix on the Helical Pile Performance in Sand

Helical piles have recently become more popular because of their technical, economic, and environmental benefits. However, the effect of adding a second helix to a single-helix pile on the foundation performance in sandy soils is variable and still not well understood. This study reports the physical modeling of a 1-g scaled helical pile in dry sand with different relative densities. Thus, the soil box was prepared with two relative density percentages (i.e., 45% and 95%). During the tests, researchers investigated how sand relative density and axial load direction (tensile and compressive load) influence the advantage of adding a second helix to a single-helix pile. The results indicated that the ratio of the bearing pressure mobilized by the pile helices in tension and compression (qh-T/qh-C) for a pile displacement of 0.1 of helix diameter is higher for piles in dense sand. In addition, it was found that the values of non-dimensional bearing factors obtained for the bottom helix of the piles are comparable with the results of previous tests. Further, the addition of a second helix could increase the capacity for both tensile and compressive loading. The tensile capacity gain was higher, ranging from 54 to 58%, compared to compressive capacity, which was only in the range of 26-28%. Eventually, the results demonstrated that although the relative gain in pile capacity by adding a second helix is independent of the relative density of the sand, it is more significant for tensile capacity compared to compressive capacity.

Automated summary

This study investigates the impact of adding a second helix to a single-helix pile on foundation performance in sandy soils. The results show that in dense sand, the bearing pressure mobilized by the pile helices in tension is higher than in compression. Additionally, the addition of a second helix increases the capacity for both tensile and compressive loading, with a higher gain observed in tensile capacity.