Bertha is hot and bothered and now we have a reason to blame for all the overheating of the nation’s largest tunnel-boring machine, which is struggling mightily to make headway on a new State Route 99 tunnel under downtown Seattle.
Washington State Dept. of Transportation officials Friday announced that contractor Seattle Tunnel Partners “discovered damage to the seal system that protects the tunneling machine’s main bearing.”
Bertha hasn’t moved substantially since early December, when the machine originally overheated, reaching temperatures of 140 degrees, about 1.5 times more than normal. At the time and for months following, officials thought an obstruction slowed the machine. But subsequent investigations both in—crews spent 158 hours of hyperbaric inspections over 12 days—and around the $80 million machine found no major obstruction, but did reveal a clogged cutterhead, partially to blame for the slowdown. But once Bertha was cleaned out and crews tried to move her at the end of January, the overheating picked right back up.
The main bearing allows the cutterhead to spin, similar to the bearing on the axle of a car, which is protected by a seal that keeps lubrication in and road grime out, WSDOT says. The tunneling machine’s main bearing is protected by 25-ft-dia. rubberized seals that function the same way.
“Investigations have shown that portions of the seal system have been damaged and need to be repaired or replaced,” WSDOT says. “Seattle Tunnel Partners and its tunneling experts are working with the machine’s manufacturer to determine the best fix for this issue.”
Expect another two weeks of investigation into the issue before STP announces a plan of attack to fix the issue and keep the main driver both lubricated and clean. Officials are hopeful that crews can get the replacement parts through the back end of the machine, otherwise they will need to bore roughly 60 ft down to the front of the machine.
WSDOT says that since Bertha is owned by Seattle Tunnel Partners, it is their responsibility to “determine the scope of the issue and the best options to repair it and get the machine moving again.”
Bertha has moved just over 1,000 ft of the 9,270-ft route. The machine, though, is still under warranty—until it tunnels 1,300 ft.—by Japan-based Hitachi Zosen Corp.
Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for TIME, Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.