Why Hochtief’s Fehmarnbelt tunnel teams are betting on giant concrete elements

Hochtief’s work on the immersed tunnel for the Fehmarnbelt Fixed Link turns the Baltic Sea into a construction site, with 217-metre concrete elements cast on land and later sunk into a trench on the seabed. What this mega-project means in practice.

Reviewed: ad hoc news Software & Services desk. Edited and checked on 2026-06-18, 15:51. Details in the imprint.

With the Fehmarnbelt immersed tunnel, Hochtief turns a quiet stretch of Baltic Sea into an industrial stage of concrete, steel, and precision dredgers. On site, the scale is almost surreal: 217-metre-long tunnel elements, each weighing tens of thousands of tonnes, lined up like ships waiting for launch.

What Hochtief is building under the sea

The Fehmarnbelt Fixed Link will be an 18-kilometre immersed tunnel connecting Rødbyhavn in Denmark with Puttgarden in Germany, designed for both car traffic and high-speed trains. Each standard tunnel element is around 217 metres long and is produced in a dedicated factory at Rødbyhavn.

Instead of boring deep below the seabed, the project team dredges a trench, sinks the huge concrete elements into it, and then backfills the top. This construction method shortens travel time between Hamburg and Copenhagen to about 2.5 hours once the link opens, according to the project owner Femern A/S.

How the tunnel elements are made

For the standard elements, steel reinforcement and formwork are assembled in long casting segments, then filled with high-performance concrete in a controlled, repetitive process. Within the permanent factory halls, temperature and curing conditions are carefully monitored to ensure uniform quality across all elements.

After curing, the hollow elements are fitted out with internal structures, road decks, and rail slabs before they ever see seawater. They are later floated out from the casting basin, towed to their final position, and lowered into the prepared trench with centimetre-level precision.

What this means on site in Rødbyhavn

On a typical day, the tunnel factory at Rødbyhavn looks more like an oversized shipyard, with gantry cranes moving rebar cages and workers guiding concrete pumps along the shuttering. Trucks deliver aggregates and cement in a constant rhythm, feeding the on-site batching plants.

Noise from welding, grinding, and concrete vibrators mixes with the low rumble of dredgers working offshore. For locals, the once quiet harbor has turned into a long-running yet carefully organized construction choreography that will last several years.

Environmental and technical constraints

Immersed tunnel construction in the Baltic brings strict environmental requirements, particularly regarding sediment spill and noise during dredging and immersion operations. Work windows are defined to protect marine life and minimize impacts on water quality and local fisheries.

Engineers also have to account for currents, ice, and long-term settlement of the seabed. That means extensive geotechnical investigations and real-time monitoring during immersion, with adjustments to ballast and positioning to keep each element exactly on line and level.

Where Hochtief fits into the consortium

Hochtief is part of the main civil works consortium that builds the tunnel’s immersed section on the Danish side, alongside large European construction partners. The group is responsible for design and construction of the tunnel, portals, and the large-scale production facilities at Rødbyhavn.

The contract value for the tunnel and factory works runs into several billion euros, spread over a multi-year period until the planned opening in the early 2030s. For Hochtief, this secures a long, predictable order book and access to engineering know-how that can be reused on future subsea infrastructure projects.

Why investors are watching the project

The Fehmarnbelt Fixed Link is one of the largest transport infrastructure projects in northern Europe, with significant political visibility and fixed long-term funding. Successful delivery can strengthen Hochtief’s reference list in complex marine projects, an area with relatively few capable global players.

Shares of Hochtief (DE0006070006) trade on Xetra in euros.

Key facts on Hochtief and the Fehmarnbelt tunnel

• Product: Fehmarnbelt immersed tunnel civil works (tunnel elements and factory at Rødbyhavn)
• Manufacturer: Hochtief AG
• Category: Software/Service/Subscription (large-scale infrastructure service contract)
• Launch: Main construction and tunnel element production ramp-up through the mid-2020s
• RRP / Price: Multi-billion-euro contract volume for the main civil works consortium
• Availability: Project site at Rødbyhavn (Denmark) and offshore in the Fehmarnbelt strait
• Target group: Public-sector transport authorities and cross-border infrastructure planners
• Highlight / USP: Long, single-tube immersed tunnel for both cars and high-speed trains, using a dedicated element factory on the Baltic coast

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