Sustainable and low-cost installation of monopile foundations for future very large wind turbines
Published: 4 February 2021
Current installation methods for monopiles face major barriers for future large monopiles. The dominant method used now to drive monopiles into the seabed is the hydraulic impact piling (hammering). The major disadvantages of the impact driving method are the generation of underwater noise that can be harmful to marine fauna and inapplicability of the method to piles extraction at the end of their service time.
Alternative installation technologies are being researched, developed, and tested at various Technology Readiness Levels (TRLs). However, none of these technologies has reached a TRL that makes it a preferred/ready solution for the installation of future XXL monopiles (with a diameter bigger than 7,5 and up to 11 meter that weigh from 1000 to 2400 tonnes) under a broad range of soil conditions. With a better understanding of their performance and a validation of the underlying models, the development of these technologies can be enabled, which should ensure that offshore wind remains one of the lowest-cost, electricity generation options.
Research of multiple alternative technologies in one project
This project will study and test various alternative technologies and aims to bring the required knowledge for these options at the same level. The techniques that are included are:
- Conventional vibratory driving, e.g. vibratory driving with a purely vertical excitation; an enhancement of this technology by means of introducing fluidisation of the internal soil column in the pile will also be tested.
- Gentle Driving of Piles: a concept which is an emerging technology that combines a vertical vibratory excitation with a high-frequency torsional shaking.
- Blue Piling, a modification to the conventional impact driving which reduces noise, will be included in the modelling of driveability and noise prediction, based on data generated outside of SIMOX.
Key topics of research are driveability, environmental and ecological aspects (with a focus on underwater noise during pile driving), and bearing capacity of the soil. Finally, the implications for decommissioning at the end of the monopile service life will be assessed.
Understand and assess multiple technologies under similar, controlled conditions
David de Jager, director of GROW: “SIMOX is unique in its comprehensive approach to understand and assess multiple technologies under similar, controlled conditions. Tests with scaled monopiles will be performed in laboratories, at two onshore sites and at a nearshore site. This is also a good example of how the GROW consortium wants to (co)operate: a joint effort to tackle a challenge that is relevant for the offshore wind industry as a whole.”
Deltares will set up and lead the geotechnical laboratory testing program in the SIMOX project. Ahmed Elkadi, geotechnical expert “To study the drivability aspects and lateral bearing capacity response of the soil to the different installation techniques we will use our state-of-the-art GeoCentrifuge. The aim of this work package is to compliment the field-testing program by closing any gaps and generating additional and necessary data sets that are required for model development and validation. The Deltares GeoCentrifuge offers the option for reproducing meaningful stress levels in the soil through the augmented gravity induced by sample spinning. Different combinations of soil conditions, pile geometry, pore-water drainage will be considered, with emphasison scenarios relevant to North Sea conditions.” In addition, Deltares will contribute to the setting up, execution, analysis and reporting of the field testing program.
A variety of consortium partners
The three-year SIMOX project is part of the GROW programme, a joint research program that initiates research and accelerates innovations in offshore wind. SIMOX is a Joint Industry Project (JIP) where knowledge is gained on a concerted effort by various industrial and research parties. The project is supported by funds from the MOOI scheme and is led by the Delft University of Technology. Deltares and TNO take active part in the research and the test campaign. The offshore contractors Van Oord, Boskalis and Seaway7 will lead the on- and nearshore tests, supported by DOT (Delft Offshore Turbine), whereas equipment manufacturers Sif, IHC IQIP, CAPE Holland and GBM Works will provide the monopiles and installation technologies. Operational aspects will be monitored and assessed by Shell, RWE and Siemens Gamesa Renewable Energy. Finally, the project will involve environmental and regional economic stakeholders in an early stage.
The subsidy scheme, which is covered by the TKI Wind op Zee, part of the Topsector Energy, is managed by the Dutch Ministry of Economic Affairs and Climate.