Silent Installation of MonoPiLEs IIB (SIMPLE IIB)

WHY

Investment costs of the support structure, including its installation, account for approximately 20% of the total investment costs of offshore wind farms. Optimising installation techniques can reduce wind energy costs significantly and improve environmental performance.

Currently the dominant installation method using impact hammering causes substantial noise, and obligatory noise mitigation measures are costly, complex, and time-consuming. Therefore, installation is prone to delays in bad weather conditions. The currently available hammers are difficult to scale to the larger monopiles that will be used in the future. In addition, hammering causes fatigue damage to the foundation pile, leading to heavier, and thus more expensive monopiles.

To mitigate these negative impacts GBM Works is developing an improved installation technique within their SIMPLE programme. Within this programme, GBM Works develops the Vibrojet®, a combination of a jetting tool (Jetgun) and a vibro hammer. The Jetgun, attached at the bottom of the foundation pile just above the pile tip, lowers the soil resistance by jetting on the inside of the pile. Vibrations are added by a conventional vibro hammer.

Before the new technique can be applied commercially, four technical aspects must be met:

1. the technology is suitable for a depth of at least 40 meters for different soil conditions,
2. the lateral bearing capacity can be accurately determined,
3. the noise level must be such that noise abatement measures are not necessary,
4. and the technique must be certified.

To date, the SIMPLE I and SIMPLE II projects have been completed. At this stage the following milestones are met for piles with a diameter up to 2 meters (scale 1:4):

1. Driveability of piles through dense sandy soils up to three times deeper and four times faster while applying the Vibrojet® compared to vibratory hammering only,
2. Noise reduction is foreseeable with measured reduction on strain levels in the pile,
3. System to control water flows inside the pile designed, to minimise the impact on (lateral) bearing capacity.

The intention is that the Vibrojet® is commercially available in 2025.

WHAT

SIMPLE I and SIMPLE II projects showed that it is necessary to simplify the Vibrojet® concept to reduce risks and costs. Therefore, we will design in this SIMPLE IIB project an improved Vibrojet® prototype for a full-scale monopile, which is representative of the current dimensions installed offshore. Launching customers will closely cooperate with the design of the prototype.

In this project, we will test the improved Vibrojet® on lateral- and axial bearing capacity. We will deploy the new prototype for onshore lateral bearing capacity tests in the GROW SIMOX project. Before these tests, we will functionally test the prototype(s) to ensure correct functioning and optimal settings for driveability.

Furthermore, the project involves extensive research to determine the design requirements based on several application areas. We will use the results of lab tests and field tests to validate models, calculations, and research study results in general.

In this project, we will also address the economic feasibility of different Vibrojet® configurations over the lifetime of a wind farm.

EXPECTED RESULTS

At the end of the SIMPLE IIB project, we will have an in-depth understanding of the Vibrojet® technology and updated models. We will have completed a functioning Vibrojet® prototype that we will test at the SIMOX locations.

We will have made production drawings for the full-scale Vibrojet® prototype. This prototype will be fabricated and tested in the SIMPLE III provisionally project planned for summer 2023.

Furthermore, a cost assessment of the Vibrojet® technique on a full scale for a specific soil, sand, and clay, will be available.

Finally, the Vibrojet® technique will be ready for certification by DNV in 2024, after the finalization of the SIMPLE III project.