Book 24, Question 82
How do builders make tunnels under rivers and seas?
One method is to dig a trench in the river bottom and sink tunnel sections built on land. The sections float like boats and then are lowered and joined in the trench. The Detroit-Windsor Tunnel was built this way in 1930. For deeper crossings, tunnel boring machines can dig under the seabed, as in the Channel Tunnel, with watertight linings to keep the water out.
More fun facts
- One way to build a tunnel under water is to make huge concrete or steel tunnel pieces on dry land.
- Workers float the giant pieces to the site, sink them into a trench dug in the bottom, join each one to the last, and cover them up.
- This kind of tunnel is called an immersed tunnel.
- The Detroit River tunnel, finished in 1910, was one of the first two immersed tunnels ever built for trains.
- The Chesapeake Bay Bridge-Tunnel in Virginia, completed in 1964, is over 17 miles long and dips into immersed tunnels under its two main shipping channels.
- The Fort McHenry Tunnel in Baltimore carries eight lanes of highway traffic through two side-by-side immersed tubes.
Sources: fhwa.dot.gov
Questions kids ask
Why does a bridge sometimes turn into a tunnel?
Tunnels let big ships pass over them, so some crossings switch from bridge to tunnel under the deep shipping channels.