Watch this 600-ton machine cut perfectly round subway tunnels under Seattle

Meet Brenda, a 600-pound machine that cuts through the earth like it’s a piece of cake.

The massive tunnel boring machine, whose face is essentially a giant rotating cutter, completed a six-month journey under Seattle on Friday.

During this time, Brenda cut one mile of tunnel for
Seattle’s new subway line extension, the 4.3-mile Northgate Link, which is under construction at a cost of $US2.1 billion. To excavate the line, two tunnel boring machines were brought in.

These machines weigh 600 tons each, and feature a rotating cutting face that’s 21.5 feet in diameter. Hydraulic cylinders push the cutters through the earth, which set concrete rings into place every five feet, giving the tunnel structure. The excavated material falls through holes in the machines’ face, and is then removed from the tunnel by conveyor belt.

Story by Tony Manfred and editing by Jeremy Dreyfuss

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