We’ve heard so much about Bertha’s teeth that it seems hard to believe we’ll actually get to see them start chewing dirt.
The 57.5-ft-dia tunneling machine—the largest ever for North America—enjoyed a bon voyage party last weekend that drew over 5,000 visitors, a final public moment before the tunnel-boring machine starts its 1.7-mile churn under downtown Seattle in a matter of days, at times 200 ft below ground.
Right now crews are putting the closing testing under wraps on the $80 million machine, tying up the final checklist components before the process that will eventually open a new tunnel to drivers in late 2015. The future State Route 99 passage removes the elevated Alaskan Way Viaduct in favor of the underground approach.
The Washington State Dept. of Transportation expects Bertha to start moving dirt on the project within days, likely on Monday, July 29.
Bertha now sits in an 80-ft tunneling pit—guests to Saturday’s event were able to venture over one of the walkways of the pit—ready to start removing dirt and laying concrete wall segments, all in unison.
While the state agency was originally hoping to start on Thursday, contractors elected to wait until Monday to get going on the project, allowing more time to place more than 3,000 sensors above ground to monitor potential soil or building movement. With 158 buildings above Bertha’s path, those sensors will prove crucial in monitoring structural integrity. But it could take time before Bertha makes it to many of those sensors, as tunneling proves a slow and tedious process.
Bertha will travel just 6.5-ft on each push before then taking a 45-minute break to build a wall segment. With well over 500 cutting tools on the head, every 400 feet of movement—that could take anywhere from two to five weeks of work—will require a check of the sharpness of the tools. For now, though, those tools prove sharp. And fresh.
Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He has also written for TIME, Popular Mechanics, Popular Science and more. You can follow him on Twitter at @tdnewcomb or visit his website here.