Apparently abrasive media cutting, using concrete driven by hypersonic air (? maybe) https://spectrum.ieee.org/energywise/energy/renewables/is-google-going-und

Apparently abrasive media cutting, using concrete driven by hypersonic air (? maybe) https://spectrum.ieee.org/energywise/energy/renewables/is-google-going-underground-with-hypersonic-tech https://spectrum.ieee.org/energywise/energy/renewables/is-go...