Pilot Project Uses Steel Fiber-Reinforced Tubbings in Construction of U5

During construction of the new underground U5 line in Hamburg, Germany, U5 GmbH will use steel fiber-reinforced concrete segments in tunnel construction for the first time in Germany, marking a major milestone for the project. These prefabricated concrete components, used to line and stabilize tunnels, reduce traditional steel reinforcement by replacing steel bars with finely distributed steel fibers within the concrete.

U5 has received an “approval in individual cases” from the technical supervisory authority for the application. As a result, the joint venture between ZÜBLIN and Wayss & Freytag will be able to install the reduced-steel tubbings in the machine-excavated tunnel tubes on the first U5 construction section beginning in 2027.

Compared to conventional segments, steel fiber-reinforced tubbings reduce steel requirements by approximately 60% while maintaining the same load-bearing capacity, durability and safety standards. In tunnel construction, where material usage and emissions are major considerations, the technology offers a significant opportunity to lower CO₂ emissions and supports the project’s broader sustainability goals.
The use of steel fiber-reinforced segments is one part of the U5’s overall CO₂ reduction strategy, which aims to cut construction-related emissions by roughly 70% compared to conventional construction methods. The project team will continue to develop and implement additional emissions-reduction measures.

Current initiatives include CO₂-optimized planning, the use of low-clinker cements and reduced-CO₂ reinforcing steel, as well as testing electric construction machinery in real-world applications. Future phases will also examine additional reductions through specialized concrete mixes for the tubbings.

With this approval on a case-by-case basis, the U5 project is taking a pioneering role in German tunnel construction and reinforcing its commitment to innovative, climate-friendly building practices.