To build underwater tunnels, prefab steel tubing is strategically positioned and sunk into place.
Tunnels tend to get short shrift when we mete out marvels of engineering. Those that dare to dunk beneath waterways are particularly impressive feats of construction.
Modern underwater tunneling begins by constructing an immersed tube within a pre-dug trench on the river or sea floor. To do this, prefabricated sections of steel tube are floated into position and strategically sunk into the trench. This technique was first used in 1903 for construction beneath the Detroit River. America also claims the longest tunnel of any kind. The New York City West Delaware water-supply tunnel runs 169 km (105 miles).
But if you want to drive your car under some serious seabed, go abroad. The Seikan Tunnel, which connects Japan’s main island of Honshu with the northern Hokkaido, measures 53.8 km (33.4 miles), of which 14.3 km (23.3 miles) lie underwater.