Immersion Engineering for the N31 Aqueduct in Harlingen

The N31 is an important transport route connecting Amsterdam, the Afsluitdijk, Harlingen and Leeuwarden. To improve accessibility in Friesland, the N31 around Harlingen was upgraded and largely constructed below ground level. The new infrastructure provides a safer traffic situation and improves the flow of both road traffic and shipping.

East of Harlingen, the N31 crosses the Van Harinxma Canal. During the recreational boating season, the existing bridge regularly caused traffic congestion whenever it had to open for passing vessels. An aqueduct was therefore selected as a sustainable and future-proof solution.

MH Poly was responsible for the complete immersion engineering of the aqueduct, with a strong focus on stability, accurate positioning and safe execution.

During the engineering phase, MH Poly carried out extensive stability analyses of the floating aqueduct element. A major challenge arose when the roof of the aqueduct passed through the waterline, causing the element to become temporarily unstable. To control this process safely, MH Poly designed an external immersion and guidance system.

MH Poly was also responsible for designing and engineering:

• Bulkheads to provide a watertight seal at both ends of the aqueduct;
• Temporary seals alongside and beneath the element;
• The hauling, guiding and positioning systems;
• The underflow system;
• Verification calculations for the prestressing system;
• Weight control and project support during execution.

The design of the temporary seals specifically accounted for potential settlement during the immersion phase. This ensured the structural safety of the aqueduct throughout the entire process.