Not your golf club, silly!
The world’s largest-diameter tunnel-boring machine. From Popular Science “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 head spins, 4-by-6-inch drill bits tear into the ground, dislodging small rocks and breaking up the soil. A set of spinning gears on the head crumbles large boulders. Scrapers then knock the dirt onto a conveyor belt that brings the haul to the surface. Bertha even has its own electric power source, so its 25,000-horsepower engine won’t disrupt the local grid. Seattle’s new double-decker highway is scheduled to open in 2015.”
Follow Bertha’s progress here as it goes through the 10 zones along its path