Episode 01 · The built world
How do you build a dry passage beneath a body of water? The answer begins with two very different ways of building a tunnel.
AI-generated conceptual illustration. Watch the full episode, then explore the explanation and sources below.
Inside the engineering
A bored tunnel passes through ground beneath the seabed. The Channel Tunnel is an example: its route runs below the seabed, rather than resting directly on it. Tunnel linings and water-management systems help maintain a usable passage.
Large tunnel elements are made on land, temporarily sealed at both ends, floated out and lowered into a prepared trench. The elements are then connected to form a continuous tunnel.
For an immersed-tunnel connection, water is pumped from the sealed space between adjacent end bulkheads. The resulting pressure difference helps press the new element against the previous one and compress the joint seal. The temporary bulkheads are removed after the connection is secured.
Go to the source
Official references for the concepts explained on this page.
How the Channel Tunnel runs beneath the seabed.
Producing, immersing and connecting tunnel elements.
An overview of the immersed-tunnel construction method.
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