Numerical study on the base shear force-displacement relationship for laterally loaded monopiles in dense sand

Large-diameter monopile is the most widely used foundation for offshore wind energy converters, which behaves as a semi-rigid/rigid pile under lateral loading. However, the current laterally loaded monopile design method recommended by API ignores the toe-kick phenomenon and the base shear force (Qb), which was developed initially for slender piles. The base shear force calibration method is still ambiguous due to the lack of lateral loading tests for large-diameter monopiles. In this study, the moment contribution of the monopile base shear force (Qb) is quantified based on the finite element simulation in dense sand. The results demonstrate that the base shear force (Qb) should not be neglected for semi-rigid/rigid monopile design, especially when the aspect ratio is no more than 4. And then, a novel four-parameter hump curve (FHC) model is suggested to establish the relationship between the shear force (Qb) and deflection (yb) at the monopile tip. The results show that the FHC model agrees well, and the Qb-yb relationship can be used in practical engineering. The systematic Qb-yb relationship establishment procedure can be applied to other sites, which may facilitate a more accurate calibration of the soil-monopile interaction for the laterally loaded monopile design.