As monopile foundations diameter scales up with the larger turbines and increasing water depth, installation feasibility is becoming a greater risk in the offshore wind industry. Experience has shown that current drivability methodologies miscalculate the soil resistance to driving (SRD) when compared to actual driving data, resulting in additional installation costs and overestimation of pile fatigue. For the current study, two hundred sixty (260) driving logs from four offshore wind farms (OWF) in different areas of the North Sea have been selected and back calculated using standard industry SRD methodologies, namely Alm & Hamre (2001), Toolan & Fox (1977) and Stevens et al. (1982). The investigated pile driving records cover a broad range of soil conditions both in terms of soil type (sand dominated, clay dominated and layered soil profiles), soil strength (easy to hard driving conditions), monopile diameters and penetration depths. The accuracy of each method has been quantitatively evaluated, with the results underpinning the industry concern of the inadequacy of the existing SRD formulations to predict the drivability of OWF monopiles and illustrating the need for development of new SRD methodologies, tailored to the Offshore Wind industry.
Georgios Perikleous, Themis Stergiou and Sandra Meissl
Keywords: pile driving, back-calculation, statistical analysis, offshore wind farms
Publisher: DFI