The contractor building the Highway 99 tunnel under downtown Seattle shared a heap of technical information on Monday about repair plans for Bertha. What remains unanswered are questions about what caused the damage that brought the massive boring machine to a standstill and whether the contractor would continue to press the state for additional money to cover repair and delay costs.
A repair schedule presented by the contractor, Seattle Tunnel Partners, at a news conference on Monday showed that the 57.5-foot diameter machine would be mining again in late March, 2015. If that schedule holds, the machine will have been stopped for nearly 16 months by the time digging resumes. Bertha first encountered mechanical problems last December, further investigation revealed that a seal system protecting the machine's main bearing had failed.
The contractor has been working closely with the machine's manufacturer, Hitachi Zosen Corp., to orchestrate the repairs. Seattle Tunnel Partners project manager, Chris Dixon, said that on June 4, he and executives from Tutor Perini and Dragados USA, the two companies that make up the contracting venture, went to Japan and met with executives from Hitachi Zosen. Dixon described it as a "critical meeting."
"We got a couple things from them; we got a commitment to meet the schedule," Dixon said. He added: "It is an aggressive schedule."
Workers at a Hitachi Zosen Corp. facility in Japan weld replacement bearing components for the Highway 99 tunnel boring machine. Photo: WSDOT
"The other thing we've impressed upon them," he said, "is that whatever repairs they carry out to fix the seal problem, we expect them to go above and beyond that, so that we have a machine that we are 100 percent confident can tunnel the remaining 8,000 feet under the city of Seattle, without any further incident."
Dixon described the seal system failure as the "root problem" that will be fixed during the repair process. The machine has seven main bearing seals, two of which will be much thicker in a new, more robust, system that Hitachi Zosen is engineering. The repairs will also involve replacing the main bearing itself, as well as adding 86 tons of steel ribs and other new reinforcement parts at the front of the machine to strenghten the area around bearing assembly. A computer system will also be upgraded to provide Bertha's operator with more information while the machine is digging, including additional sensor data about the status of the bearing seal system.
When the seals failed, contaminants, such as grit and water, entered the area around the main bearing, which is one of the machine's more important components. Weighing approximately 88-tons and measuring about 33-feet in diameter, the main bearing allows Bertha's cutter-head to spin and bore through the earth. Seattle Tunnel Partners has decided to replace the bearing even though it is unclear how severely it was damaged when the seal system failed.
Bertha is currently about 60 feet underground in Pioneer Square. The machine is stopped about 1,000 feet into the planned tunnel path, which stretches roughly 9,000 feet between SoDo and South Lake Union.
To access and fix the machine, Seattle Tunnel Partners will build a concrete-lined pit between the Alaskan Way Viaduct and Pier 48, just south of South Main Street. The pit will be about 120-feet deep and roughly 83-feet wide. Once the pit is excavated, Bertha's cutter-head, along with other parts at the front of the machine, which together weigh almost 2,000 tons, will be removed. A crane-like "modular lift tower," which is shaped like a goal post, will straddle the pit and raise the hefty components to ground level in a single lift. The lift tower will then rotate the cutter-head assembly and set it face-down on the ground so the repairs can be performed. The pit is scheduled to be finished in September and the cutter-head removal is slated to take place in October.
Like what you just read? Support high quality local journalism. Become a member of Crosscut today!