Improving the lateral capacity of monopiles in submarine clay

The European offshore wind sector has been undergoing tremendous growth, resulting in offshore wind farms having larger wind turbines that are located further away from the shore in harsh environmental conditions. To cater for the resulting higher loads, the current trend has been to continually increase the size of the monopile, which is the most popular foundation type. However, this is not viable in the long term given the current installation technology. This paper presents the results of three-dimensional finite-element analyses investigating the improvement in the lateral capacity of a large-diameter monopile in clay when used in combination with hybrid features and rock armour. Non-skirted reinforced concrete and steel footings, a skirted steel footing and steel fins were assessed under a combination of vertical, lateral and moment loads expected at an offshore wind farm location with a water depth of 30 m. The findings, based on shear and bending moment developed in the monopile and mobilised soil resistance, indicate the skirted steel footing and fins to be the most effective in enhancing monopile lateral capacity at serviceability.