WT’s Marijn Dekker on his involvement in a new paper for the special edition of Ocean Engineering

With WT’s Geotechnical Engineers Marijn Dekker and Mohammed Al Maadheedi contributing to the latest issue of the Ocean Engineering journal; a special edition surrounding Geotechnical Considerations for Offshore Wind, we caught up with Marijn to find out more about the significance of the work carried out for the paper and why it is important for the industry.

Why is the research conducted within this paper important for the offshore wind industry?

The study we did for this paper helps us to support developers of offshore wind farms with the planning of transport & installation operations. Jack-up vessels, used for foundation and turbine installations, need to get within a close enough distance of the installation position to allow for successful installation. However, they also must stay a certain distance away when installing a turbine on a piled foundation as to not disturb the foundations with the spudcan footings, which are pressed into the ground to provide stability to the vessel when jacking up. This trade-off of requirements requires close teamwork between the design and installation teams to find the optimum approach. In simple ground conditions the penetration of a spudcan and the effect on the soil around it can be predicted well, however in soft and layered soil conditions, as we see for instance in Taiwan, the process is more challenging to understand. We managed to build a calculation model that could match experiments for these complex conditions, so we could be confident that our model can be used for planning safe vessel operations for turbine installation but also take away any conservatism in the distance between the vessel and a foundation.

Why are the findings from this paper important for WT’s clients?

Our model showed that a sand plug can be pushed down underneath the spudcan in soil conditions with sand above clay when it is pressed down, which means that a spudcan penetrates less deep than and causes less disturbance to the piles of the foundation than otherwise would be predicted. Not only does this information mean our clients and installation contractors can pick the right installation vessel for the job, it also helps our clients to set and supply the right criteria and clearance distance from foundation to their installation contractors.

What were the main findings from the paper?

We built a finite element model in the software Plaxis to describe spudcan penetration in sand overlying clay including formation of a sand plug underneath the spudcan, using a so-called updated mesh formulation. While our model is relatively straightforward and quick to calculate compared to more advanced FE models using for example coupled Eulerian–Lagrangian techniques, we showed that we could still accurately capture the sand plug formation at different stages of spudcan penetration, as well as the displacement field around the spudcan, which can be used to determine the impact of spudcan penetration on nearby piles of a turbine foundation.

To read Marijn & Mohammed’s paper ‘Numerical modelling of sand plug formation during punch-through of a spudcan footing’, click here. The full piece is available to read for free until the end of August 2023.

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