N57 Middelburg

Client:
Ministry of Transport, Public Works and Water Management
Location:
Middelburg
Number of elements:
1
Immersion:
2008
Specials:
No ballast tanks
Projecten - N57 001
Projecten - N57 002

Project information

The N57 Walcheren project involves the renovation and repositioning of the existing N57 motorway in the municipality of Middelburg in the Dutch province of Zeeland. The section in question runs from the A58 national trunk road near Nieuw- en Sint Joosland (to the south) along the north-eastern edge of Middelburg and Serooskerke to Vrouwenpolder. In Middelburg itself, the road crosses the Canal through Walcheren via an aqueduct. This aqueduct includes an immersed tunnel segment that allows the N57 motorway to cross under the canal.

The immersed tunnel segment was prefabricated in an excavation on the southern approach ramp. The team installed the segment at the tunnel site in accordance with the OTAO® procedure (a process trademarked by Strukton). Following construction, the team raised the water level in the excavation to the level of the adjacent canal and floated the segment. After removing the temporary watertight wall of the southern approach ramp and the northern abutment, the tunnel segment was moved through the excavation using a winch configuration and towed along the canal for a stretch of some 165 metres in the direction of the northern abutment.

There, the project team immersed the segment by pulling it into position. By adopting this innovative pulling approach, there was no need to install – and subsequently remove – ballast tanks in the segment. The final stage of the immersion involved the construction of foundations for the segment in the shape of an inundated sand flow. A permanent layer of concrete ballast in the segment itself and backfill around the immersed structure ensure that the segment remains fixed in place.

Measurement systems

Geocon used a system based on total stations to position this segment.

In addition, the company visualised the tensile forces in the winches and jack pressures during immersion.

Geocon also provided data for the pressure levels, concentration and flow velocities in the flooding conduit on the inundation pontoon. Together with the supporting forces in the hydraulic jack rods this allowed for a real-time visualisation of the flooding process.