How the world’s largest underwater tunnel is being built | BBC News

Key Concepts:

• Femon Belt Tunnel: A pre-fabricated road and rail tunnel connecting Denmark and Germany under the Baltic Sea.
• Tunnel Segments: Pre-fabricated concrete and steel sections of the tunnel, each over 200 meters long.
• Pin and Catch System: A precise system for aligning and connecting tunnel segments underwater.
• Environmental Impact: Concerns and lawsuits related to the project's environmental effects.
• EU Infrastructure Plan: The Femon Belt Tunnel as part of a broader EU initiative to improve transportation links.

Project Overview:

• The Femon Belt Tunnel is a mega-project under construction in southern Denmark, designed to link Denmark and Germany via a tunnel under the Baltic Sea.
• It is described as Europe's biggest construction site and the world's longest pre-fabricated road and rail tunnel.
• The project's cost exceeds 7 billion EUR, primarily financed by Denmark, and is part of a larger EU plan to enhance travel links between northern and southern Europe.

Construction Details:

• The construction site spans the size of 600 football pitches.
• The tunnel will be 18 km long, running under the Femon Belt in the Baltic Sea.
• The tunnel segments are being molded from steel and concrete inside three enormous halls.
• Each segment is over 200 meters long, and 90 such segments will be linked together.
• The amount of steel required is equivalent to that of 50 Eiffel Towers.

Segment Assembly Process:

1. Steel Structure Assembly: The initial step involves assembling the metal structure of the tunnel segment.
2. Concrete Molding: The steel structure is then molded with concrete.
3. Element Formation: Nine of these molded structures are combined to create a single tunnel element.
4. Underwater Placement: Each segment, weighing 73,000 tons, is floated out to sea and lowered into a trench dug into the seabed.
5. Precision Alignment: The segments are placed with 15 mm precision using a "pin and catch" system. This system involves arms grabbing the element and dragging it slowly into place.

Benefits and Impact:

• The tunnel will reduce the rail journey between Copenhagen and Hamburg from 4 and 1/2 hours to just 2 and 1/2 hours.
• It will replace the 45-minute ferry sailing with a drive of less than 10 minutes.
• The project aims to boost the local economy.
• It is expected to reduce carbon emissions by shortening travel distances by 160 kilometers.
• The tunnel is considered a more secure option than a bridge due to risks associated with wind and ship collisions.

Challenges and Considerations:

• The project has faced repeated delays due to lawsuits and environmental opposition.
• The seabed's soft bedrock made drilling infeasible, leading to the choice of a submerged tunnel.
• The deep water (30 meters) allows for the passage of large ships.

Notable Quotes:

• "Everybody's the winner because obviously businesses they will be closer connected and then by not having an extra distance to drive you will also cut in carbon because traveling 160 kilometers less."
• Regarding the pin and catch system: "We have to be very very careful that it's placed just in front of the next one."

Timeline:

• The project has been in the pipeline for almost two decades.
• The tunnel is expected to open in 5 years from the time of the report.

Conclusion:

The Femon Belt Tunnel is a massive infrastructure project poised to significantly improve transportation between Scandinavia and Central Europe. Despite facing environmental concerns and construction challenges, the project is progressing, promising reduced travel times, lower carbon emissions, and economic benefits for the region. The innovative engineering techniques, particularly the pre-fabricated tunnel segments and the "pin and catch" alignment system, highlight the scale and complexity of this undertaking.