A combined ArcelorMittal sheet pile solution helps protect the Yser River from storm floods

Adapting to stormier times

Storm surges are one of the main natural threats in the North Sea region. Today, coastal ports are most at risk of flooding due to heavy storm weather. To protect the coast and coastal area from heavy storms, the Flemish Government approved the Masterplan for Coastal Safety in 2011. This plan included the construction of a storm flood barrier at the mouth of the Yser River in Nieuwpoort. After in-depth studies, a horizontal barrier with a clearance width of 38 metres was planned.

A rotating barrier...

The movable steel barrier construction rotates around a horizontal axis. When open, the barrier is sunk in a concrete sill at the bottom of the Yser River. The steel barrier rotates between two cast steel shafts which are anchored in concrete abutments connected to the banks of the Yser.

At high tide, the water level reaches 5 metres above the average low tide water level (TAW). Combined with a heavy storm – on average twice per year – the water level of the Yser can rise to more than 6 metres TAW. At that point, the storm surge barrier is rotated 90 degrees, closing off access to the harbour. The barrier can even handle a rise of up to 8 metres TAW, but that situation statistically occurs only once every thousand years. The project design considered a sea level rise of 80 cm by the year 2100.

For maintenance purposes, the barrier can be rotated 180 degrees into the horizontal maintenance position. Large lateral ducts (bypass sewers) were built in the abutments. These can handle additional flows, keeping the current velocity at spring tide below 3 knots and limiting the impact on recreational boating.

...between two pits built with a combined steel sheet pile solution

The two building pits for the abutments were made of combined walls. Each pit consisted of 53 tubular piles Ø1420 x 21.6 mm in S 460 MH with a length of 31.5 m and infill sheet piles AZ® 28-700 in S 240 GP with a length of 26.5 m. The tubular king piles were installed with a PVE 2350 VM vibratory hammer and driven to final elevation with an IHC Hydrohammer S150. Due to the strong water pressure on the combined walls, the C6 interlocks of the tubes and the middle interlocks of the sheet piles were filled with Beltan® Plus sealant.

For each pit, 42 tubular foundation piles Ø1270 x 16 mm in S 355 J0 with a length of 12.9 m were installed with an overlength of 8.6 m to drive them with a vibratory hammer above the water level. They were driven 9 m into the tertiary clay using a PVE 250M vibratory hammer.

The tubes were dredged and partly filled with concrete. On top of the combined wall, a strutting system was installed with Ø1067 x 14 mm tubes as compression struts and HEM700 wailing beams.

After the dredging of the building pit, a 2-metre-thick layer of underwater concrete was poured. Subsequently, the pit could be drained to level -12.6 m TAW. The foundation piles were cut at level -12.6 m TAW and a 3-metre-thick concrete floor slab was poured. The cut off piles were reused to fabricate the foundation piles of the second building pit.

Project timeline

In April 2022, the 4500-t concrete sill was installed between both abutments. In addition to the building pits, other steel combined walls, sheet pile walls, and tubes were installed for the quay walls at both embankments, the current conducting walls, a construction pit for the bypass sewers, the guiding walls, and the dolphins. The project started in February 2018 and was completed in 2025.

ArcelorMittal products delivered

Tubular piles: 7323 tonnes (for abutment pits: 3217 tonnes, other: 4106 tonnes)
Sheet piles: 2914 tonnes (for abutment pits: 658 tonnes AZ 28-700, other: 2256 tonnes)