Large diameter monopile buckling due to localized force. A numerical study.

In the last decade, the industry of fixed offshore wind farms has developed significantly, leading to important reductions of the global cost of the plants. Generally speaking, about 30% of the total cost of a wind offshore plant, including the installation activities, is related to foundations. In the view of optimising the management of the plant, strong efforts have been done to reduce the costs of the foundation, preserving the planned design while assuring a safe and reliable performance. From the practical point of view, the most diffused foundation, i.e., the monopile, is of special interest. Cost optimisation of the foundation suggests to increase the diameter and to reduce the wall thickness of the monopile, increasing the risk of pile tip damage, particularly frequent in soils where localized inclusions like flints or boulders are present. A higher potential tip damage is the undesired counterpart of the geometry optimisation and it may induce unacceptable economic consequences. This study, based on numerical analyses, is focalized on the buckling of the pile tip subjected to a variously inclined localized force, acting on the edge of the pile base. Results are collected in diagrams, which can be used in design procedures.