Investigating installation and post-installation performance of vibro-driven monopiles in sand: centrifuge modelling and numerical analysis

The majority of bottom-fixed offshore wind turbines are supported by monopiles. Vibro-driving offers an al-ternative to impact driving, with advantages including rapid installation in particular in sand, lower acoustic emissions and mitigation of pile run risk. Important design uncertainties remain, however, regarding driveabil-ity prediction and post installation lateral stiffness. This paper presents preliminary results of a combined ex-perimental and numerical investigation into these aspects. Vibro-installation and post-installation performance under lateral loading has been investigated using a vibro-driver specifically designed for a geotechnical centri-fuge. This has enabled experimental investigation of vibro-driven monopiles under a range of controlled and repeatable conditions that can be related to prototypes via established scaling laws, with example results dis-cussed here. In addition, the results of large and small displacement numerical modelling have been combined to provide further insight into the stress field and void ratio changes that underpin the response both during vibro-driving and in operation.