Review of torque models for offshore helical piles

Abstract

Helical (or screw) piles, sometimes defined as anchors, are a piled system consisting of one or multiple helices welded along the shaft. Piles are installed by applying a torque to the shaft. The pile is rotated into the soil and the rate of advancement should be an amount equal to the pitch for each rotation in order to minimize the disturbance of the original soil. Torque is maybe the most important parameter to be assessed during pile installation. In fact, torque and uplift capacity are directly proportional. Generally, torque depends on the soil conditions and on the geometrical features of the pile. Torque increases with sand density, installation depth, friction angle of sand, pile shaft and helix diameters. The geometry of the pile has a strong influence on the torque, the larger the helix-to-shaft ratio is, the larger the torque will be. In offshore applications helical piles are being considered as a valid alternative. However, one of the issues is still related to the assessment of the installation torque values. Several torque models have been considered and critical evaluated. Some simple comparisons among selected torque models have been also done and discussed.