Assessment of the soil resistance to driving models for vibro installation of large diameter monopiles

The majority of the offshore wind turbines constructed to date are founded on monopile foundations. As monopiles’ diameters have increased to 10m and above, there is an increasing concern over the impact of noise generated by using impact hammers. There are several innovative concepts for pile installation which result in reduced noise and vibrations. A number of these concepts include conventional vibratory hammers to overcome the soil resistance and allow installation to the design depth. A driveability assessment is required to provide the correct specification for vibratory hammers. An essential component of a driveability model is to estimate the static resistance to driving (SRD). SRD is analogous to the axial capacity of a pile during driving. It represents the cumulative increase in the shaft capacity associated with further pile penetration and also encompasses a base resistance that is associated with each driving increment. In this paper, a number of published cases of vibro installations are compiled and compared to predictions using commercial software GRLWEAP implemented with a number of SRD models. The pile diameters consider a range from 4.0m to 6.5m and include piles installed in the Dutch sector of the North Sea, where a number of offshore wind farms are currently under construction. Our study assesses the predictive capability of these models and shows that the soil resistance is sensitive to the penetration speed of the pile.