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 bigger and the size of the monopiles also grows. These huge piles need to be driven into the ground for a significant part of their length. Organization and execution of this process are challenging, time-consuming and costly. And above this, the noise emitted by pile driving and the disturbance of soil will increase. So, developing a new technology of piledriving is necessary.
Gentle Driving of Piles (GDP) is a project led by TU Delft that is executed within the GROW program. The method for pile driving they developed is based on utilizing a certain vibration unused so far in the industry for pile driving. The vibration is the result of low-frequency and high-frequency vibrations exciting two different modes of motion of the monopiles. By doing this the monopile gets a little bit thinner. This makes it easier to drive the pile into the soil. Traditional impact methods lead to the opposite: monopiles expand a little when knocking or hammering on it, which of course make it harder to drive the piles. So, with the novel installation method, the pile installation process can be made as efficient as possible.
The test, which started in October at the second Maasvlakte, was part of the test and demonstration phase of the GDP-project. This successful proof of concept demonstrated that GDP is a very promising method with a lot of potential advantages compared to the other methods. GPD aims to not compromise soil bearing capacities and pile penetration speed. Most importantly, the GDP technology has the potential to reduce the emitted driving noise significantly.
In the field test, the consortium tested the newly developed GDP shaker. This shaker installed four of the eight piles on the test site. Three other piles were installed by impact hammering and one was installed by vibratory driving. This way the consortium can compare the shaker to traditional vibratory and impact hammers.
Besides the test and demonstration phase, the GDP project has a theoretical phase. This part aims to explain the physics governing the novel pile installation technique. For this, the piles and soil on the test site are equipped with sensors that generate an unprecedented set of data. With these, numerical tools are being developed and validated so the installation procedure for new offshore wind farms can be optimized.
With the GDP method, the consortium is working on important improvements on pile installation. Most important are the benefits for the environment: noise reduction, less disturbance for the soil and the GDP method strives to install the piles faster than the current ways of pile driving. Above that the method has the potential to lower the costs of installation, the GDP method will reduce the emitted noise below a level that would make it possible to install piles the entire year.
Future development steps
Within this project, the theoretical phase is ongoing with the aim to predict the drivability, emitted noise and analyse bearing capacity of future piles drive. Future steps towards implementation of the technique will focus the application of the technique in other soil tubes and upscaling for offshore use.
TKI Wind op Zee
According to Andrei Metrikine, the support of TKI Wind op Zee was vital in the GDP project. It helped TU Delft to connect with the industry. Maxim Segeren, Business Developer Offshore Renewables of TU Delft, confirmes this. According to him TKI Wind op Zee helped them to get access to the whole network in the Netherlands. Together with its support to GDP, TKI Wind op Zee provided a base for real innovation in the development of offshore wind in the Netherlands.
Find out more about GDP.