How do they build the underwater tunnels?

Question

I really find underwater tunnels amazing! These tunnels have rounded shapes usually,ı can guess why they a rounded shape,but ı dont know how the workers build these tunnels without drowning?

Answer 1

Prefrabricated tunnel segments are loaded onto cargo ships, be floated into position, then sunk into the designated area. Workers do not personally go under water.

Answer 2

Here's one way.... Immersed Tube Technique The immersed tube method, a version of the cut and cover technique, is a cheap and easy way to construct a tunnel under water -- and it's generally the fastest way. Here's how it works: Dredging machines cut a trench in the riverbed. Then one by one, preassembled, watertight tubes are floated out and lowered into place over the trench. Divers bolt each segment together to form the complete tunnel. The tunnel is then covered with a steel-and-concrete casing to prevent the tunnel from floating and to protect it from damage caused by passing ships. Underwater tunnels around the world, including Hong Kong's metro tunnel system and San Francisco's Bay Area Rapid Transit tunnel, were put together like this.

Answer 3

they build tunnels block by block . they made each block seperately on earth ,then they attach blocks under the sea using cables.they put each block using huge cranes .attaching each block under sea is very difficult task .they also attach blocks
by screwing them with each other by whatever means.