A far more 'sensible' approach to rapid tunnel construction was experimentally tested in the 70s. The Rapid Excavation And Mining(REAM) project showed how high

A far more 'sensible' approach to rapid tunnel construction was experimentally tested in the 70s. The Rapid Excavation And Mining(REAM) project showed how high speed kinetic projectiles could be used to to rapidly fracture rock to dig a tunnel. This is a fancy way of saying that someone dug a tunnel through rock by repeatedly shooting at it with a tank.[0] This was found to be impractical due to the cost of gun powder. However, a company has proposed a supersonic ramjet accelerator instead of a conventional gun to accomplish this. SCRAM accelerators use a specially shaped projectile that acts as a SCRAM jet when it's inside a tube full of fuel/oxidizer, which may be much cheaper than gun powder.[1] They have started to demonstrate fracturing rock walls with this approach. [0]https://apps.dtic.mil/sti/pdfs/AD0757116.pdf https://apps.dtic.mil/sti/pdfs/AD0757116.pdf [1]https://www.hypersciences.com/applications/ https://www.hypersciences.com/applications/