The most used support structure in the North Sea are monopiles. The current dominant technique to install monopile is impact driving, which is considered a sub-optimal method. In the SIMPLE (Silent Installation of MonoPiLEs) programme, GBM Works is developing the Vibrojet® installation method, combining the vibro technique with water jetting inside the monopile. This new installation method will reduce installation costs and noise levels, preventing harmful impacts on marine life. The Vibrojet® is also easier to apply than impact hammering, as it eliminates the complex and time-consuming use of common noise mitigation measures such as bubble screens.
A jet gun delivers the jetting part of the Vibrojet®. Attached to the bottom of the foundation pile above the pile tip, the jet gun lowers the soil resistance by fluidising the soil inside the pile. A conventional vibro hammer adds vibrations.
Before the new technique can be applied commercially, specific technical aspects must be met, amongst others:
The figure below provides an overview of the various projects forming the SIMPLE programme.
To date, the SIMPLE I and SIMPLE II projects have been completed, and the SIMPLE IIB project is ongoing.
At this stage, the following results have been achieved:
During the SIMPLE-III offshore test campaign, noise measurements will be made to determine the reduction in noise of Vibrojet® installations compared to those with the vibro-technique and impact driving. The data generated will deliver sufficient confidence to install piles in a commercial project by bringing down the risk to an acceptable level.
The offshore tests will be designed in close cooperation with project partners representing the whole value chain. The tests are required to demonstrate the technique's performance and will increase the predictability of the Vibrojet®. Specifically, we will increase confidence in scaling factors for the jetting technology and improve understanding of required flow rates to minimise the fluidisation volume.
The tests will be performed with a pile of 4 m diameter, 62 m length, wall thickness of 45mm and a weight of 145mT. In total, there will be three tests with the Vibro technique only and three with the Vibrojet®. Each test is concluded with a decommissioning test with the Vibrojet®.
The SIMPLE III project will bring the Vibrojet® technique to technology readiness level (TRL) 7. By testing the technology under large-scale offshore conditions in sandy soils, enough data will be generated to achieve Technology Qualification by DNV. The project will compare the Vibrojet® and the vibro and impact hammering on costs, underwater noise and fatigue damage in the pile. Furthermore, the refusal depth will be assessed of the Vibrojet® technique compared to that of the Vibro installation.
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This project is supported with a subsidy by the Dutch Ministry of Economic Affairs and Climate Policy. Find more project information at the TKI Offshore Energy website.