Excavation work started this week on Velsen Beach to remove seven ‘obstacles’ from the sand at a depth of several metres. Those ‘targets’ were located during the earlier investigation for unexploded explosives from World War II. The objects will be removed for the construction of the sea cables, which TenneT will use to bring the energy of the offshore wind farm Hollandse Kust (west Beta) ashore from 2026.

Next autumn, south of Wijk aan Zee on the Velsen beach (near De HangOut), work will start on the connection of the Hollandse Kust (west Beta) wind farm. “Using technology attached to a drone, we looked down into the soil to a depth of about ten metres,” Kelvin Bastiaan, project manager for marine cables Hollandse Kust (west Beta) on behalf of TenneT, explains. “This is how we found 13 ‘suspect locations’ in the beach. After test drilling, seven targets remained, which we will now excavate.”

Work site

By investigating and removing obstacles on the cable route, TenneT wants to create the safest possible situation on land and at sea for both employees and the power cables. Bastiaan: “South of Wijk aan Zee, near surf and kit school DeHangOut, we have cordoned off a working area on the beach for a period of about seven weeks. This area is guarded 24/7 and beach visitors can simply walk around it.”

Excavation pit

Excavating the objects, according to project manager Bastiaan, is done using so-called ‘excavation pits’. “Because you don’t want to dig large holes in the beach, we use a formwork that lowers itself into the sand while digging. This creates a five-by-five-metre pit that we can bring to a depth of over seven metres. We store the released soil right next to the pit. Outside working hours, we naturally cover this excavation pit well.”

Laying

When the excavation is carried out to within half a metre of the property, you are now below the groundwater level. Bastiaan: “Using detection equipment, a diver first establishes the exact location and then the object is manually exposed without touching it. If it is an unexploded explosive, then according to protocol the Explosives Clearing Service of Defence is called in. Is it rubble or scrap metal? Then we excavate the object and then dispose of it.”

Atlantic Wall

Based on previous experience at Heemskerk/Wijk aan Zee, Kelvin expects that there is a chance that parts of the WWII German beach barrier, which was part of the glorious Atlantic Wall, will be found here too. “In addition to some construction debris from the beach houses, we then also came across some reinforced concrete piles. These turned out to be parts of so-called tetrahedrons. Beach barriers meant to stop landing vehicles.”

Layer by layer

Once an ‘obstacle’ has been removed from the beach, the pit will be sealed again with the released sand. “Using a vibrating needle and/or on waters, we will properly compact the sand package again – layer by layer – to avoid quicksand-like situations,” says Bastiaan. “With each layer, we remove part of the formwork. Once all seven targets have been removed, we will of course check the ground conditions one more time very carefully before removing the equipment.”

Offshore

Most of the NGE survey was, of course, carried out offshore. Simultaneously with the excavation work on the beach, contractor Boskalis (of contractor combination NBOS) is removing some obstacles off the coast for the laying of the sea cables. Bastiaan: “These are not explosives, but things like boulders, fishing nets, steel cables or debris. A large crane on a ship is used for this, which can excavate 36 cubic metres with one shovel. Afterwards, they check the route again at sea with a ripper tooth. This tine is pulled through the seabed up to three metres deep to check that everything is gone.”

Stay informed

Do you find it interesting to keep track of the connection of the offshore wind farms and the continuation of the study on Velsen beach? Then download the TenneT ConstructionApp free of charge from the App Store (iOS) or Google Play (Android). This way, you will receive up-to-date information about the work on an ongoing basis.

Source: https://www.tennet.eu/
Image source: Courtesy of TenneT

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