When Bertha rotated its massive teeth for the first time in 2013 it was the largest tunneling machine in the world. Now 4 years later, Bertha has finally broken through to the other side, after chewing through 1.7 miles (2.73 km) of Seattle underground.
The tunnel will house a double-decker highway in the heart of downtown Seattle. The machine ran into major issues after the first few months and came to a grinding halt for two years as engineers struggled to repair the massive machine. To fix it, they had to work on it where it lay underground—which meant digging an 11-story-deep pit.
On April 4, 2017 the 57.5 ft (17.5 m) wide cutting head broke through the giant retaining wall on the north end of the tunnel. You can read more about the project on NPR.
