Study on the posture control strategy of sinking and penetration characteristics of hexagonal thick-walled multi-compartment bucket foundation

Abstract

This paper is based on the measured data of an actual offshore wind power thick-walled concrete multi-compartment bucket foundation (MCBF) successfully penetrated and installed under the construction environment of harsh marine conditions, combined with the actual sinking operation steps, several important stages of the foundation sinking posture in the water are investigated, and proposed a set of in-water sinking posture control strategy and the corresponding engineering recommendations. The field-measured penetration resistance is compared with the undrained shear strength (S_u) and cone penetration (CPT) method of introducing the resistance reduction coefficient, and the resistance reduction coefficient is verified by the measured penetration differential pressure. The results show that the foundation total inclination can be effectively levelled by the sinking posture control strategy of the lowest side compartment, the three high side compartments and the mid-compartment exhaust, and by the levelling control strategy of only the highest side compartment and the mid-compartment exhaust during the important stage of the sinking posture. When the thick-walled MCBF is sunk to within 1m from the mud surface during high wind and wave conditions, the levelling control strategy is adopted to ensure that the total inclination is within 0.5° when contacting the mud. Before the top cover of the foundation entering the water, the beam structure should be evenly flooded and the total inclination should be controlled within 1°, when the foundation is off the bottom of the vessel, the total inclination should be stabilized to within 0.2°. For the thick-walled MCBF, the two methods can accurately predict the penetration resistance and penetration differential pressure when the resistance reduction coefficient is taken as 0.5. The research in this paper provides construction guidance and experience reference for offshore wind power projects of penetration and installation under harsh marine conditions.