Non-vertical spudcan impacts on a dense sandy seabed: improving design through centrifuge modelling

Bottom-fixed wind turbines are often installed from a mobile jack-up vessel which is supported on spudcan foundations while on location. During emplacement, the spudcans may impact the seabed at an angle resulting in large stresses transmitted to the leg-hull connections. It is difficult to predict these stresses, particularly for dense sandy seabeds where uncertainty remains regarding shallow penetration resistances developed during high shear rates and reduced drainage. This paper considers the problem through centrifuge modelling with a dense sand sample. A model spudcan was attached to a ‘swinging’ loading arm to simulate dynamic, non-vertical impacts with realistic trajectories. Impact velocities of 1-2 m/s were targeted by setting the spudcan in-to a free-fall swing where a MEMS accelerometer and Hall effect sensor captured the entire dynamic event. Bending and axial gauges allowed force components at seabed impact to be resolved, helping to address cur-rent design uncertainty with respect to peak impact forces and bearing resistance.