Currently, monopiles are mostly driven into the seabed by hydraulic impact piling (hammering). This causes too much noise during driving and each hammer blow has a high impact on the monopile. Offshore wind turbines are getting bigger and the size of the monopiles is also growing. These huge piles have to be driven into the ground for a considerable part of their length. The organisation and execution of this process is challenging, time-consuming and costly. And on top of that, the noise of piling and soil disturbance increases. Developing a new technology of piling is therefore necessary.
GDP
Gentle Driving of Piles (GDP) is a project led by the TU Delft and carried out within the GROW programme. The pile driving method they developed is based on the use of a particular vibration that has not been used in industry for pile driving until now. The vibration is the result of low-frequency and high-frequency vibrations generating two different modes of movement of the monopiles. As a result, the monopile becomes somewhat thinner. This allows the pile to go into the ground more easily. Traditional striking methods lead to the opposite: monopiles expand a little when they are knocked or hammered, which of course makes it more difficult to drive the piles. The new installation method can therefore make the pile installation process as efficient as possible.
Testing
The test, which started in October at Maasvlakte 2, was part of the test and demonstration phase of the GDP project. This successful proof of concept showed that GDP is a promising method with many potential advantages over the other methods. GDP aims to avoid compromising soil bearing capacity and pile penetration rates. Most importantly, GDP technology has the potential to significantly reduce the driving noise produced.
In the field test, the consortium tested the newly developed GDP shaker. This shaker installed four out of eight piles at the test site. Three other piles were installed by impact hammering and one was installed by vibratory piling. In this way, the consortium can compare the shaker with traditional vibratory and impact hammers.
Theory
Besides the test and demonstration phase, the GDP project has a theoretical phase. This part aims to explain the physics of the new pile installation technique. For this purpose, the piles and soil at the trial site are fitted with sensors that generate an unprecedented set of data. This will be used to develop and validate numerical tools to optimise the installation procedure for new offshore wind farms.
Benefits
With the GDP method, the consortium is working on significant improvements in pile installation. Most important are the environmental benefits: noise reduction, less soil disturbance and the GDP method aims to install the piles faster than current methods of piling. In addition, the method has the potential to reduce installation costs; the GDP method will reduce emitted noise below a level that would allow year-round pile installation.
Future development
Within this project, the theoretical phase is ongoing with the aim of predicting the driving characteristics, radiated noise and analytical bearing capacity of future piles. Future steps towards implementation of the technique will focus on applying the technique in other soil pipes and scaling up for offshore use.
TKI Offshore Energy
According to Andrei Metrikine, the support of TKI Offshore Energy was essential in the GDP project. It helped TU Delft connect with the industry. This is confirmed by Maxim Segeren, Business Developer Offshore Renewables at TU Delft. According to him, TKI Offshore Energy helped them access the entire network in the Netherlands. Together with its support to GDP, TKI Offshore Energy has laid a foundation for real innovation in offshore wind development in the Netherlands.