Engineering
The Grout Behind Tunnel Shields in Underwater Crossings
Quick fact
In underwater tunnel construction, grout is forced into the void behind the tunnel shield under high pressure almost simultaneously as the shield advances, hardening quickly to prevent sudden ground collapse and water flooding. This grout often must set within hours while being constantly saturated with water.
Why this is interesting
You've likely travelled through an underwater tunnel without ever seeing the material that makes it possible. What fills the gap between the tunnel and the earth beneath a river?