Petra uses super-hot gas to penetrate bedrock. The method could make it cheaper to move utilities underground—and make electric lines safer

https://www.wired.com/story/new-tech-cuts-rock-without-grinding-it/

"cuts through rock without grinding Into it... a mix of gas and heat above 1,800 degrees Fahrenheit that breaks rock into small pieces. Sensors attached to small rods touch the rock, but the excavation is carried out by the heat and gas. Using this tech, which was created in part by one of Tesla's cofounders, Petra wants to make tunneling through bedrock cheap enough to encourage utilities to bury electricity and other lines underground"