In one corner, weighing in at 8,000 tons, with a cutterhead height of 57.5 feet, and a machine length of 326 feet, Big Bertha!!! You definitely don’t want to be in the other corner!!
Last month, Bertha, the world’s biggest “earth pressure balance boring machine” finished digging a gigantic tunnel under the city of Seattle to replace a damaged highway viaduct. The completed tunnel stretches 1.75 miles – or 9,270 feet – long and is 5-stories tall!! And now, with the job done, she’s being pulled apart.
Bertha finished her billion-dollar dig on April 4th, exited from the ground into a 90-foot-deep disassembly pit. With the rubbled cleared, the $80M machine is being dismantled and carved into 20-ton pieces to be removed by crane, melted down, and recycled. Disassembling Bertha will take up to 5 months, with the cutterhead alone requiring over 35 lifts to be fully removed from the pit.
While Bertha’s final breakthrough was perfectly aligned, the project is 29 months behind schedule. Two years of repairs were required after the machine hit a piece of metal piping and overheated. Crews had to dig down from the surface to retrieve parts for maintenance. Soon after, operations were halted again to fill in a large sinkhole that developed above the tunnel.
Fortunately, digging proceeded smoothly since the repairs in 2015. A crew inside Bertha built circular tunnel walls as they moved along with the machine. Next will come construction of the 4-lane, double-decker roadway, installation of mechanical and electrical systems, and connecting the tunnel to existing ramps. Finally, there will be intensive inspections and commissioning. Above ground, the viaduct will be demolished and a new waterfront area developed. The State Route 99 tunnel is expected to be open for traffic by 2019.
Despite a job well-done (after repair modifications were implemented), Bertha will be no more. Some thanks, huh? However, as cities move away from elevated roadways, tunneling will offer a unique alternative, requiring similar machines. Operating and maneuvering restraints will likely prevent future boring machines from being much bigger than Bertha, but even if they are larger or faster, few are likely to be quite as groundbreaking.
How impressed are you by Bertha?? Let us know what you think about this massive project in the comments below!!
And here are a couple cool vids if you want to see Bertha in action!!