[mad_as_he$$]

Won’t work. There is to much heat required to set the material. Mountain Tunnel is 18.3 miles long and 10 foot in diameter.

[Pontiac]

Won’t work. There is to much heat required to set the material. Mountain Tunnel is 18.3 miles long and 10 foot in diameter.

Sure it wouldn’t be easy.

I can imagine that the tunnel would be relined in sections. The surface of the tunnel would have to cleaned, any cracks grouted and then preheated before the liners was extruded in to place.