Estimation of uplift capacity and installation power of helical piles in sand for offshore structures

In the offshore field, helical piles are being considered as a novel offshore pile system because of their flexibility regarding ease of installation and the large uplift capacity they can generate. This paper analyzes 120 cases in sand for different friction angle values, from 30 to 45°, considering five uplift forces, i.e., 5 to 25 MN, and three different wing ratio values (i.e., helix-to-shaft ratio). By using two different uplift capacity equations, the resulting embedment depths, depending on soil conditions and uplift axial force, are obtained. Torque was assessed with a model considering the relationship with the uplift capacity for deep helical piles in sand. Installation power was also initially assessed taking into account the torque and the crowd force. Calculations show that torque increases with the increasing helix diameter for the same geotechnical properties of the sand. Also, during installation, induced shear stress in the pile may be too high if the standard yield strength of steel is assumed.