The effect of pile slip on underwater noise emission in vibratory pile driving

Due to the growing demand in offshore wind, increasing numbers of foundation piles are planned to be installed in the coming decades. Monopiles driven by impact hammers have a large environmental impact on aquatic life. Vibratory pile driving is a promising alternative that generates less noise nuisance. Despite the lower levels of noise expected, modeling of noise radiation from vibratory piling is still required due to the large size of the foundation piles used nowadays and the changes in the radiated spectrum of the noise. The existing models used to assess the noise emission are calibrated against impact piling and are not accurate when it comes to noise radiation from vibratory installation. Existing models either represent the sediment as an acoustic fluid or, when the seabed is modelled as elastic medium, they couple the soil and pile displacements fully at their interface. The effect of both these assumptions on the radiated noise still needs to be verified in vibratory pile installation. Additionally, the effect of the secondary noise path, i.e. noise channeling into the seawater via the soil, is expected to play a more significant role in vibratory pile driving because more energy is concentrated at the lower frequencies. In this paper, a pile-water-soil model to predict the noise emission due to vibratory pile driving is developed which describes the soil as an elastic medium and allows the pile to move relative to the soil during the pile driving process. To maintain a computationally efficient solution method, the effect of friction is linearized via a spring connection between soil and pile. Finally, a study is conducted and the effect of the slip on the noise emission is studied in detail for the first time.