Scheldetunnel (c) Lantis

The Scheldt in miniature

The Scheldt tunnel will be the Queen piece of the Oosterweel link: it will close the ring on the north side by connecting the left and right banks of the Scheldt. A daring feat, since the tunnel will be built in Zeebrugge and then towed to Antwerp and immersed on the Scheldt soil. With a physical scale model, we can test how the immersion of the various tunnel elements can be done safely.

While the construction dock in Zeebrugge is being built, we are taking a closer look at the positioning of the Scheldt tunnel. The design was made on the basis of detailed computer simulations, supplemented by experience from the past. Now we are going to verify these results with a physical test. Physical and digital testing has never been done before and will give us a lot of insights and guarantee a robust design of the sedimentation system.

Go with the flow

For this, we recreated the Scheldt at Oosterweel in a basin on a scale of 1/60 in HR Wallingford's hydraulic lab. One tunnel element was also realistically recreated. Not only in terms of shape and weight, but also with the same immersion material that will control the element, such as anchor wires, hoisting wires and immersion pontoons. With pumps, we imitate the tidal flow as accurately as possible.

Measuring is...

With this simulation to scale, we want to test the positioning and immersion of the elements. Because there is a considerable tidal current in the Scheldt, we measure the forces that the tunnel element has to deal with due to the current, using sensors on the scale model and in the immersion material. This is how we determine the capacity of all the components that must keep the element in place during the operation.

Everything under control

During the immersion process the Scheldt at Oosterweel will be temporarily closed to traffic. Afterwards, navigation will be possible again. However, shortly after the immersion, such a tunnel element rests on temporary mooring points while we apply a definitive foundation bed underneath and backfill the tunnel trench. The tunnel is therefore fixed to a limited extent during this period. We use a model ship to test the impact of a passing ocean-going vessel. Thanks to these tests, we know what measures we may have to take to keep the tunnel stable until the foundation and backfilling are complete.

A complex and technically difficult process

We want to be sure that we always have the tunnel elements under control during the immersion process. They must therefore be positioned correctly to within a few centimetres. By testing all this in a physical scale model, we are confident that the design is safe and that our approach works.

 

Pictures (c) Lantis

Scheldetunnel (c) Lantis

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