SEATTLE — Sometime this fall, a huge vertical shaft lined with 84 concrete pilings, designed to hold back the slurry that defines underground Seattle, will be finished, and a Mr. Fix-It operation unlike any other will begin.
The world’s biggest tunnel-boring machine, nicknamed Bertha — which hit a pipe and was damaged in mid-December after only 1,000 feet of excavation — is down there in the dark, awaiting what may well be the world’s biggest industrial rescue operation.
“When you have such a big machine, you have a big intervention,” said Youssef Hashash, a professor of civil and environmental engineering who teaches tunneling at the University of Illinois at Urbana-Champaign. When things break, he added, “it all scales up, and it scales up the challenge as well that you have to overcome.”
On paper, the complex plan looks like a cross between a ballet and a monster-truck pull in its combination of delicate details and heavy-torque engineering. First, a rail-mounted crane will be inched up to the shaft’s edge. Then, a 2,000-ton piece of the boring machine’s front assembly will be raised up and laid down on the waterfront. There it will be repaired under the supervision of Japanese managers from the company that built it, reinforced with 200 or so tons of new steel and slowly lowered back down into the 120-foot-deep pit. And then things really get tricky. Project managers liken reattaching Bertha’s front end to putting a rebuilt, souped-up engine into the family Volvo.
“An engine mounts in there a certain way, it weighs a certain amount, everything connects in a certain way — now you’re going to put it back in the car and it’s a little different,” said Matt Preedy, the deputy program administrator for the $3.1 billion Alaskan Way Viaduct Replacement Program, of which the tunnel is the biggest part. “So obviously they’re doing a lot of planning and engineering work to ensure that it will fit back in there,” he added.
If all goes according to schedule, tunnel work could resume next March, 16 months after tunneling was stopped. Until then, the rescue itself — the cost of which, along with delays, could surpass $125 million — has become its own drama within the broader saga of the tunnel.
Engineers around the world were closely watching Seattle’s tunnel even before Bertha ran into big trouble. The largest diameter tunnel-boring machine ever built — about five stories across, or 57.5 feet — Bertha was designed to dig under Seattle’s waterfront to allow the city to replace an aging viaduct. The project was given urgent priority after an earthquake in 2001 revealed instability in the elevated roadway, which was built in the 1950s. Tearing down the viaduct will also open up the city’s waterfront to new development.
What exactly happened to Bertha, as it moved forward on its 9,000-foot journey, is in bitter dispute, with huge dollar totals at stake. The tunnel’s contractor has argued that a buried 8-inch diameter steel pipe in the machine’s path led to problems of grit and rock infiltrating the seal and bearing system, but state transportation experts believe the pipe had nothing to do with the trouble at all.
The rescue operation (workers call it “the intervention”) began in late spring with construction on the shaft to reach Bertha. Workers have been sinking pilings in a ring to prevent the shaft from collapsing, using 24,000 cubic yards of concrete — enough for a medium-size office building. Once that ring is complete, digging on the shaft will start.
When the shaft is ready, Bertha, which is damaged but still operational, will be turned back on so she can chew through the concrete pilings to reach the center of the shaft. There, the machine will rest on a cradle where workers can detach the front end and hoist it out.
Beyond Bertha’s problems, the tunnel plan itself has also become intertwined with a larger debate about the city’s future, as the biggest building boom in at least a decade is reshaping the skyline and adding thousands of new residents — and their cars.
But here is the hard truth about the tunnel: It is not being built to reduce vehicle congestion (improving safety is its main goal) and it might actually make traffic worse.
A traffic study group created by the city and the state said in March that up to 58,000 drivers a day could divert onto local streets or Interstate 5 depending on the toll structure and rate imposed for the tunnel. About 110,000 vehicles a day were using the viaduct before the excavation began, free of charge, but the tunnel project hinged on a toll to pay for at least part of its cost and upkeep.
Meanwhile, the full-boil debate over the cause of Bertha’s problems, not to mention the finger-pointing about who should ultimately pay for the repairs, has yet to begin.
The steel pipe that the machine struck in December was put there by the state in 2002 to monitor groundwater but was not identified in the contract, said Chris Dixon, the project manager at Seattle Tunnel Partners, the tunnel builder. That, he said, makes it the state’s responsibility.
But the state has refused Seattle Tunnel Partners’ request for $125 million to pay for Bertha’s breakdown, maintaining that the pipe’s existence was well known in reports and studies that construction managers should have known about if they had looked.
Preedy said the contract issues were “a distraction” from the central issue at hand, to get the machine fixed and back to tunneling. “Those questions will be answered in time,” he said.
Dixon said the dispute was rather like Bertha herself, waiting for its day in the sun.
“It’s lurking in the background, waiting to appear,” he said.