A Sensitivity Analysis on the Parameters Affecting Large Diameter Helical Pile Installation Torque, Depth and Installation Power for Offshore Applications-Article

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The study theoretically evaluates large-diameter, single-helix piles as potential offshore foundations in clay. It examines a 500 mm shaft with helix-to-shaft ratios of 1.5, 2.0, and 2.5, target uplift capacities of 10, 15, and 20 MN, and clay strengths up to 500 kPa. Two methods estimate uplift capacity and required embedment depth, while two models estimate installation torque. Installation power is calculated from torque and rotational speed; a Monte Carlo analysis assesses uncertainty in predicted depth.<br /><br />Results show that larger helices generally reduce the depth needed to achieve a target uplift capacity. Accounting for clay sensitivity and strength loss caused by installation increases the required depth, but reduces resistance to installation and therefore torque. The Japanese capacity method, which does not account for remoulding, predicts depths around 15–25% shorter than the Das–Seeley method. Torque predictions vary with the selected calculation method, particularly when remoulding is omitted. Increasing the steel–clay interface friction angle has only a modest effect on torque.<br /><br />The analysis also identifies structural limits: for the assumed pile and A36 steel, installation torque may exceed the pile’s yield capacity at uplift targets of 15 or 20 MN, depending on the models used. Possible remedies include thicker or stronger shafts, or using more piles per foundation leg. The Monte Carlo results indicate substantial variability in estimated pile length due to uncertainty in soil properties.<br /><br />Overall, the findings suggest that offshore helical pile feasibility depends strongly on the capacity and torque models, soil variability, and pile structural strength. The study is theoretical, and the authors caution that offshore design guidance is limited; field validation and careful assessment are needed. It also does not model long-term strength recovery or aging.

Keywords

helical piles

offshore foundations

clay uplift capacity

embedment depth

installation torque

single-helix pile

soil sensitivity

Monte Carlo analysis

pile structural strength

capacity methods