A study of the axial load behaviour of helical piles in sand by frustum confining vessel

Helical piles as screwed piles are a popular solution for removable or recyclable foundations that support road or offshore structures. In this study, the frustum confining vessel developed at the Amirkabir University of Technology (FCV-AUT) is used to study the axial behaviour of helical piles as the physical modelling of their apparatus. Three models of helical piles are made of hollow galvanised iron pipes (diameter of 34 mm and length of 85 cm), to which single-, double- and triple-helical plates (diameter of 70 mm) are welded. The influences of the number of helices and the geometry of the piles on failure mechanism are studied at two different densities of Babolsar sand by conducting 12 tensile and compressive loading tests in FCV-AUT. The piles are instrumented using strain gauges in order to study internal axial load distribution during pile loading. Two static analysis methods are used to verify the experimental results. The results have shown that the FCV has good performance in modelling the behaviour of helical piles under compression tests. It is also known that the shear resistance parameters of the surrounding soil are more affected by three- or multi-helix piles with higher relative densities.