Seafloor screw piles

The total capacity of the offshore wind sector in Europe grew by 18% in 2018 alone.[1] The prospect of larger turbines and deeper waters present a challenge to the current methods of driving foundation “pin” monopiles into the seabed floor.[2,3] Screw piles (helical piles) have been proposed as a potential innovative alternative for offshore wind installations in depths of 30-60m.[4] 

Even in shallow waters, fabrication and installation of offshore foundations make up 20% of the overall project costs, and these costs rise exponentially with increasing water depth.[5] Screw piles for jacket-based foundations - those that are used in deeper waters - are forecasted to reduce installation time and cut costs by 33%.[6] Screw piles can easily be removed and reused, which will facilitate the eventual decommissioning or repurposing of the structures.[7,8]

Screw piles are already sufficient in terms of both tensile and compressive strength to be used as foundations.[2,4] Current methods of hammering monopiles continue to raise concerns about their disturbance to marine mammals, the seabed, and subsea plant life.[2] Screwing produces less noise and vibration during installation. However, screw piles are currently limited in diameter, and mostly suitable for installation sites in soft and medium soil types.[9] As offshore wind is moved into deeper water, screw piles may offer a solution to the challenges of driving piles in deeper waters.

When will it become accepted practice to use screw piles instead of foundation piles for offshore wind installations?

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References:
[1] Komusanac, I., Fraile, D., and G. Brindley (2019), Wind energy in Europe in 2018
[2] Screw piles for offshore wind (2020)
[3] Spagnoli, G. (2013), Some considerations regarding the use of helical piles as foundation for offshore structures. In Soil Mechanics and Foundation Engineering
[4] Al-Baghdadi, T. (2018), Screw piles as offshore foundations: Numerical and physical modelling.
[5] Kitzing, L., & Morthorst, P. E. (2015), Trends in offshore wind economics – the past and the future. In Proceedings - 14th Wind Integration Workshop
[6] Davidson, C., Al-Baghdadi, T., Brown, M., Knappett, J., Brennan, A., Augarde, C. E., Blake, A. & Ball J. (2018), Centrifuge modelling of screw piles for offshore wind energy foundations. In 9th International Conference on Physical Modelling in Geotechnics
[7] MacLean Dixie HFS. (2020), Petroleum / Pipelines.from MacLean Dixie HFS
[8] Byrne, B. W., and Houlsby G. T. (2015), Helical piles: an innovative foundation design option for offshore wind turbines.
[9] Saleem, Z. (2011), Alternatives and modifications of Monopile foundation or its installation technique for noise mitigation.
More information:
Wind Europe (2018), Offshore wind in Europe grew 25% in 2017
Passon, P., Branner, K., Larsen, S. E., & Hvenekær Rasmussen, J. (2015), Offshore Wind Turbine Foundation Design
Davidson, C., Al-Baghdadi, T., Brown, M., Brennan, A., Knappett, J., Augarde, C., & Ball, J. (2018), A modified CPT based installation torque prediction for large screw piles in sand.

By Matthew J. Spaniol