Tunnel-boring machines are some of the most massive forms of tunneling equipment in the world, and "(p)eople are intrigued by the mix of brute force, cutting-edge technology and unknown goings-on beneath their feet," writes Daniel Michaels. The article talks about TBM technology and how these machines can "excavate a tunnel and line the tube automatically, staffed by only about 20 workers." Michaels also cites several record-breaking projects in the United Kingdom, Norway and Switzerland, including the Delaware Aqueduct, the longest tunnel in the U.S.

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