We have used this company in the past for fixing large water pipe in place.
They use what is essentially a sock they soak in plastic resin and then press against the inside of the pipe with water pressure.
It then cures in place adhering to the inside of the pipe.
You lose a little bit of inside diameter but the resin usually has less friction to water flow so you don’t lose much flow. .
The size of the tunnel may be too large but I don’t see why the process could not be scaled up.
There’s a difference between a leaking pipe and a tunnel that is caving in.
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.