Lateral bearing behaviour of vibro- and impact-driven large-diameter piles in dense sand

Monopiles are the preferred foundation solution for offshore wind turbines in sandy soils below shallow and moderate water depths. The piles are commonly installed using impact driving. A severe disadvantage of this installation method is that high noise levels occur in the water, which are a risk to animals living in the sea. Approval authorities are known to impose statutory requirements to mitigate this risk, placing a financial burden on installation. Vibratory driving is an alternative installation method that reduces noise emission levels significantly. However, the effect of vibro-driving on the bearing behaviour of piles under lateral loading is largely unknown. Full-scale load tests were conducted in predominantly dense, non-cohesive, saturated soil to investigate the differences between impact-driven piles and vibrated piles regarding their lateral bedding behaviour. CPTs and pile head load-displacement curves were recorded and evaluated. In general, it was determined that the bearing behaviour of vibro-driven piles is heavily dependent on the parameters of the installation process. For the installation parameters used in the test campaign, two vibro-driven piles showed a weaker bedding reaction in comparison to the impact-driven piles, although one vibrated pile installed with unintentionally different parameters showed an only slightly weaker behaviour under primary loading and even increased unloading and reloading stiffness. Furthermore, it was observed that an indication regarding the differences in the bedding resistance can be obtained via CPT measurements before and after installation, since the installation procedure considerably affects the relative density of the soil around the pile.