A silent and fast method for installing monopiles
GBM Works has developed a method to install monopiles in a silent and fast way.
The vibratory hammer with a jet gun is not only cheaper and less harmful to marine life, but the process is also kept strictly under control. After successful tests on land, founder Ben Arntz is now preparing to put it to a near shore test this autumn, together with an impressive consortium.
For which problem have you found a solution?
“With the advance of 10+ MW wind turbines and increasingly strict noise standards, the existing pile-driving method with hydraulic hammers for monopiles is under a lot of pressure. For example, in Germany with its strict noise standards, 160 Db at a distance of 750 meters is the maximum. With pile driving the noise level rises up to 180 Db. Extra measures are needed, such as bubble screens or a wall around the monopile. These measures are expensive and time-consuming to install. The pile is also damaged by the hydraulic hammer, which means that larger piles are needed than actually necessary. This year Germany will use a vibratory hammer for the first time to install monopiles of more than 1000 tons. The noise level is probably just below 160 Db. Therefore, no additional measures are required, although it is close to the limit. In addition, the vibrating hammer requires a lot of power and it is not certain that it will reach the desired depth through solid clay layers.”
What is the core of your solution?
“The combination of a vibrating hammer and a jet gun. The jet gun is attached to the bottom of the monopile with clamps for installation in the cylinder. Seawater is injected at the bottom. As a result, the sand or clay is fluidized, which temporarily reduces friction. At the same time, the hammer drives the monopile into the ground. Once the monopile is installed, the ground in the inside sinks back into place. On the outside, the soil remains untouched. That is crucial. It is the bearing capacity of the ground on the outside that has to withstand the horizontal forces of wind and strong currents on the wind turbine. It depends on the composition of the soil how high the water pressure and how strong the vibrations must be to get the monopile to depth. That is why we monitor the entire process with countless (pressure) sensors."
What is so innovative about your technology?
“We integrate two existing techniques that are not yet applied offshore, and certainly not with piles with a diameter of 8 meters. Really innovative is that we closely control the entire process: the water pressure during injection, the vibration strength, the soil condition, the behaviour of the soil on the inside, outside and bottom of the monopile. We have an accurate prediction model that we feed with measurements. From the installation vessel, we see what is happening in real-time. We can make adjustments if necessary, to keep the process in constant balance.”
What are the benefits of your system?
“Our system produces much less noise. Water injection is silent and because the soil on the inside offers no resistance, the vibrating hammer only has to work at half force, producing much less noise. Tests with a 12-meter long monopile on land have shown that the vibrations are reduced by 70%. In any case, the noise is considerably less than 160 Db; how much exactly an offshore field test should reveal. Because the monopile is less damaged, lighter monopiles will suffice. In addition, the speed at which you can install wind turbines is increasing. Our method is 3-5 times faster than conventional pile driving; apart from the time savings of avoiding noise-reducing measures. Our installation requires much less electrical power and offers more certainty that the monopile will reach the correct depth. Our method makes installation possible where normal vibrating hammers cannot reach target depths. All of this results in significant cost savings and less damage to marine life.”
How far are you now?
“Last September, we carried out tests with a 12-meter-long pile on the Maasvlakte. We showed that the principle works. This September, as part of the SIMPLE II project, we are going to test our installation nearshore on a 35-meter pile, including noise measurements and validation of our model. We are part of the SIMOX-project, in which almost the entire offshore wind industry is represented. As part of the GROW research program, this consortium will investigate whether innovative techniques are a commercially feasible and sustainable installation technique for XXL monopiles in five years' time. At the beginning of February 2021, this project received 4 million euros from the Top Sector Energy.”
What are your challenges?
“It is a technical challenge to drive through dense sandy and clay soils: whether the installation is strong enough to push the monopile to the desired depth. In addition, it is not easy for a small company to gain a foothold in a capital-intensive sector with a quite conservative way of working. You need a lot of evidence and financing is a huge challenge. Even though we are part of Simox, we still have to put in a lot of money ourselves.”
What are your next steps?
“If we prove in September that our installation is suitable for all soil types, that it actually works and offers benefits, we are on TRL 6-7. We hope to be at TRL level 8 with a full-scale offshore demonstration in the summer of 2022. We are looking for wind farm developers and contractors to do a demonstration project together. We are in discussion with both parties.”
What is the added value of TKI Wind op Zee and Offshore Wind Innovators?
“We have received funding from the HER and HER + scheme for the projects we have done so far. When submitting and approving the Simox-project, we also benefited greatly from TKI Wind op Zee network. It is an important player in the innovation landscape. It ensures that the market is opened up more quickly to innovations, also for companies that are not yet established.”
This article has been prepared in cooperation with the Offshore Wind Innovators.
Product information: www.gbmworks.com.