The World's Largest Tunnel-Boring Machine

25,000-horsepower Bertha in Seattle's double-decker highway project. 
(Popular Science  Posted 11.11.2013)


Built in Japan and reassembled in the U.S., Bertha is digging the 1.7-mile tunnel by advancing at an average of 35 feet a day. As its 57.5-foot-wide (~17.5m) head spins, 4-by-6-inch drill bits tear into the ground, dislodging small rocks and breaking up the soil. The new double-decker highway tunnel is scheduled to open in 2015.


Height: 57.5 feet
Weight: 7,000 tons
Length: 326 feet

Reference:
1. Follow Bertha - Washington State Dept. of Transportation;
2. Inside the world's tunnel boring machine - Gizmag