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. © the author(s), under exclusive licence to the iran university of science and technology 2023.