Silent and Circular Decommissioning of Monopiles (SIDE-MP)

WHY

As the first generation of offshore wind farms approaches the end of its operational life and monopile foundations continue to increase in size, the need for practical and environmentally responsible decommissioning methods is becoming more urgent. Such methods should enable the safe removal of foundations, maximise recovery and reuse of materials, and minimise disturbance to the marine environment.

This need is growing rapidly. European offshore wind capacity exceeded 30 GW in 2023 and continues to expand, while the earliest wind farms are approaching the end of their 20 to 30-year design life. In the coming decades, thousands of turbines will require decisions on repowering, lifetime extension or decommissioning. In countries such as the Netherlands, legislation requires sites to be restored to a condition comparable to their original state, reinforcing the importance of effective and environmentally sound full-removal techniques.

One promising approach for decommissioning is the use of controlled water jetting. Controlled water jetting combined with vibration, known as Vibrojet®, is a technique originally developed for low-noise monopile installation. By reducing shaft resistance in sections of the pile that do not contribute to bearing capacity, this method can facilitate both installation and removal. Trials in the preceding GROW SIMOX and SIMPLE III projects demonstrated that monopiles can be successfully extracted using jetting and/or vibrojetting, indicating strong potential for low-impact decommissioning solutions that support material reuse and environmental protection.

WHAT

The project will investigate controlled water jetting as viable method for the full removal of offshore wind monopile foundations at the end of their service life. It will build on previous installation-focused trials by further developing, optimising and validating the technique specifically for decommissioning conditions. The primary objective is to establish a safe, efficient and environmentally responsible approach that enables complete monopile extraction while maximising material recovery and minimising seabed disturbance.

The project will be executed through a phased programme that combines fluidisation modelling and proof of concept lab tests. A previously developed fluidisation model will be adapted to simulate jetting configurations for decommissioning. Laboratory tests will be carried out to validate the fluidisation model and demonstrate monopile extraction using jetting. Instrumentation will be deployed to monitor pore pressures, total pressures, extraction forces and changes in soil state (porosity) during decommissioning.

Ultimately, the results of the numerical modelling and laboratory tests will be translated into practical design recommendations for offshore monopile extraction. Recommendations will address jetting configurations, energy requirements, sediment disturbance limits and environmental considerations

EXPECTED RESULTS

The project will deliver the following key results:

• An extended fluidisation model capable of simulating external jetting scenarios relevant to monopile extraction;
• A validated laboratory dataset characterising soil-fluid interaction under jetting;
• A comparative analysis between model predictions and experimental results;
• A set of draft guidelines for the investigated low-impact monopile extraction method, with direct relevance to decommissioning practices in the Dutch offshore sector.