Investigation of spacing effect in group helical piles with laboratory tests

Helical piles are steel foundation systems that are practical to transport and install, and have been gaining popularity in deep foundation applications. Owing to their advantages such as sustainability, rapid installation, and applicability in various soil types, they are increasingly preferred over conventional piles. Although this system can be implemented as single or group piles, the literature contains extensive research on single helical piles, whereas studies on group helical piles are relatively limited. In this study, the effect of pile spacing on the axial compressive load-bearing capacity of group helical piles with 1x2, 1x3, 2x2, and 1x4 configurations was investigated through laboratory model tests. The tests were conducted in loose sand, examining not only different pile spacings but also the effects of parameters such as the number of helical plates (N), helical plate diameter (D) and group configuration. Load–displacement relationships were obtained, and the ultimate load-bearing capacity was evaluated according to the %5D failure criterion. The results indicated that increasing pile spacing leads to a reduction in load-bearing capacity, group configuration of helices, as well as an increase in the number and diameter of helices, enhances the load-bearing capacity.