We once focused on the tunnel Bertha, the continent’s largest tunnel-boring machine at 57.5-dia-wide, was digging. But that all stopped in December 2013 when Bertha broke down just 1,000 ft into the 9,000-plus-ft project.
Now we’ll talk Bertha again until at least March 2015 when the Japanese-made machine hopes to tunnel again. But from now until then, the discussion will center on repairs.
The latest work plan released from Seattle Tunnel Partners, the contractor on the project, shows they plan to replace the damaged bearing seal system with a “more robust system,” completely replace the $5 million main bearing, install enhanced monitoring systems and add steel to strengthen the machine to accommodate the new seal system.
Keep in mind, officials still aren’t sure what exactly caused the seal failure and subsequent stoppage of Bertha due to overheating and bearing damage.
But the above changes, while the most substantial, aren’t the only planned between now and sometime in 2015, the same year the tunnel was originally scheduled to finish construction.
As part of the repair, the 7,000-ton machine will get even bigger with the widening of openings at the center of the cutterhead. The soil-conditioning injection system will improve and new bit- and wear-resistant steel will get added to the cutterhead.
Crews will extend the machine’s agitator arms in the mixing chamber.
For an animated look of the changes, visit here.
Seattle Tunnel Partners must get check-off from the Washington State Dept. of Transportation while proving the machine’s structure can withstand all the loads from the surrounding ground and it own operation, the seal design calculations add up, the design for the revised conditioner injection systems and cutterhead openings work and there is an updated operations plan that includes the enhanced instrumentation and monitoring.
Of course, STP will also need to complete a full testing program for the machine stopped 60 ft underground in South Seattle near the city’s stadiums and waterfront before it can restart tunneling sometime in 2015.
First, though, crews are still building the underground walls of a circular pit to access the machine for the needed repairs.
It looks like we won’t talk tunnel for a while. The focus remains on Bertha.
Tim Newcomb is Engineering News-Record’s Pacific Northwest contributor. He also writes for Popular Mechanics, Sports Illustrated and more. You can follow him on Twitter at @tdnewcomb or visit his website here.