Bertha’s latest problem? She broke the seal
by Bill Lucia
Looking into the Highway 99 tunnel from the "launch pit." Credit: Bill Lucia
Bertha’s got a busted bearing seal, Washington State Department of Transportation officials said on Tuesday. The massive boring machine digging the Highway 99 tunnel has now been at a near-standstill under downtown Seattle for two months.
The seal protects the machine’s main bearing, which allows its 57.5-foot wide “cutter-head” to turn. Seattle Tunnel Partners, the contractor digging the tunnel, idled the machine on Dec. 7 after it encountered unusual resistance and heat-sensors showed high readings. During the investigation that followed the stoppage, workers discovered that Bertha’s cutter-head “spokes” were clogged with soil. The contractor moved the machine forward about 4-feet last week and sensors again indicated it was running hot. In the days that followed, workers discovered the damaged seal.
WSDOT could not offer specifics on the amount of money or time that would be required to fix the seal, or whether the machine’s main bearing might have been damaged by grit. Program Administrator, Todd Trepanier, did say that it was possible to replace the seal either with the machine in place, or by digging it up. Based on the terms of the project’s “design-build” contract, that decision, he said, is up to the contractor.
“The investigation associated with the main bearing is still ongoing,” Trepanier said.
The main bearing assembly for the one-of-a-kind boring machine cost $5,178,397, according to project budget documents.
There are a variety of factors that could explain why the machine’s cutter-head spokes were jammed with dirt, Trepanier said, including soil-type, additives injected into the mined soil and the machine’s speed. “These are constantly changed and modified,” Trepanier said. "It’s a very sophisticated issue.”
The nearly $90 million machine, still technically belongs to its manufacturer, Hitachi Zosen Corp. The project contract was structured so that the company would maintain ownership of Bertha until 200 six-and-a-half foot concrete tunnel liner rings were in place. At that point, ownership would be transferred to Seattle Tunnel Partners, which is a joint venture between Dragados-USA and Tutor Perini.
After the machine moved forward last week, crews installed the 149th ring. Hitachi Zosen Corp. representatives, Trepanier said, are onsite, working with Seattle Tunnel Partners.
The machine currently sits 60-feet below South Main Street, about 1,000-feet along the roughly 9,000-foot planned tunnel path. Bertha is scheduled to emerge in South Lake Union in late 2014. A four-lane highway inside the tunnel is set to open by the end of 2015. In a conference call with reporters today, Trepanier said Seattle Tunnel Partners had not yet given any indication that the roadway would not be completed on time.