How underground tunnels are built?
Channel: Amania Tv
Date: 26/11/2017

November 2017:

Welcome back Amaniacs, Did you know that The channel tunnel of the UK has the longest undersea portion of any tunnel in the World? This makes us wonder how are underwater tunnels constructed? You see, Under the water is some kind of ground. If you're lucky, that ground is sturdy clay or chalk that's easy to mine through by digging underground, and holds its shape long enough to quickly reinforce the tunnel with brick walls or with iron rings. If you're not lucky, that ground may be unstable silt, or really hard granite. In such situations, a river can be diverted through a temporary channel and the tunnel can be dug and covered over with a brick or concrete roof while the riverbed is dry. Hence, you either build it with water or simply divert the water, build it and then bring back the water.

Attributions:

Doh De Oh by Kevin MacLeod is licensed under a Creative Commons Attribution licence (https://creativecommons.org/licenses/by/4.0/)
Source: http://incompetech.com/music/royalty-free/index.html?isrc=USUAN1100255
Artist: http://incompetech.com/

Subtle Library by Fabian Measures (http://freemusicarchive.org/music/Fabian_Measures/) is licensed under a Creative Commons Attribution licence ( https://creativecommons.org/licenses/by/4.0/)
Source: http://freemusicarchive.org/music/Fabian_Measures/Emotion_Music/Subtle_Library

https://upload.wikimedia.org/wikipedia/commons/5/57/Tunnel_picto.svg
By Roulex 45 (Own work) [GFDL (http://www.gnu.org/copyleft/fdl.html) or CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)], via Wikimedia Commons