Tunnel Boring Machine a 200-ton rock-chewing machine designed to carve through rock First used in a tunnel in 1957 to carve a sewer tunnel through shale and limestone in Toronto, Canada

Did you know?
Tunnel boring machines (TBMs) are very picky about the rocks they chew through. This is why geologists must monitor the rock at the head of every tunnel. On good days, TBMs can bore through rock at a whopping rate of 250 feet a day. But when TBMs bite into rocks they don't like, they grind to a halt and conk out for good. Many tunnel engineers have been forced to abandon their TBMs because they can't back them out of the tunnel!

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