Tunneling With A Mechanical Worm On Steroids

Mexico City was founded on an unstable lake bed at the bottom of a volcanic crater. The soil is so soft that the city has sunk thirty feet in the last century alone. Blasting to create tunnels would topple buildings, so the government turned to giant tunnel boring machines capable of churning out 44 million horsepower--the same force could launch a space shuttle. | http://www.sciencechannel.com/

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