Underwater tunnels are often constructed using massive tunnel-boring machines (TBMs). These incredible machines, sometimes called "moles," are the key to efficiently creating tunnels beneath the sea.
Tunnel Boring Machines (TBMs)
The primary method for building underwater tunnels involves using TBMs. Here's a breakdown of how they work:
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Cutting through the Rock: A TBM has a rotating circular plate at its front, equipped with numerous disk cutters. As the machine moves forward, this plate rotates, and the cutters grind away at the rock and soil.
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Simultaneous Construction: Behind the cutting head, other parts of the TBM simultaneously perform other crucial tasks, like:
- Erecting tunnel support: Sections of the tunnel lining (typically concrete or steel) are immediately installed to prevent collapse.
- Removing debris: A system is in place to continuously remove the excavated material ("spoil") from the tunnel.
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Precision Navigation: TBMs use laser guidance systems to ensure they stay on the correct course, crucial for long underwater tunnels.
Why TBMs?
- Speed and Efficiency: TBMs can bore through rock much faster than older methods.
- Reduced Disruption: They cause less surface disturbance compared to other construction techniques.
- Safety: While not without risks, using TBMs reduces the need for human workers to be in hazardous environments for extended periods.
Alternative Methods
While TBMs are now prevalent, other methods, particularly for shorter tunnels or specific ground conditions, are sometimes used:
- Immersed Tube Tunnels: Pre-fabricated tunnel sections are floated to the site, sunk into a prepared trench on the seabed, and then connected.
- Cut-and-Cover: A trench is dug, the tunnel is built within the trench, and then the trench is covered over. This method is typically used in shallower water and closer to shore.
Example
A prominent example of underwater tunnel construction is the Channel Tunnel (or "Chunnel") connecting England and France. TBMs were used to bore the majority of this tunnel.
