When the world’s biggest drill grinds a path under downtown Seattle, its first few weeks will be the most precarious.
The Highway 99 tunnel machine will push the limits of technology by navigating an obstacle course of soft soil, seeping saltwater, road pilings and historic brick buildings as it starts a 1.7-mile underground voyage from Sodo to South Lake Union.
Engineers here have learned from mistakes at the nearby Brightwater sewer tunnel and the Beacon Hill light-rail tunnel, and from successes and failures around the world. But if megaprojects teach us anything, it’s that new mistakes are waiting to be made.
Bertha will grind through the front of its launch pit by the end of July. An opening celebration Saturday attracted Gov. Jay Inslee and a crowd of about 5,000 curious people.
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The $80 million machine, built by Hitachi-Zosen in Japan, measures 57 feet, 4 3/16 inches in diameter — led by a cutter disc seven times as large as a Sound Transit rail tunnel. The 322-foot-long colossus, including conveyors to whisk excavated dirt out the back end, had to be shipped in 41 pieces and reassembled.
Its route begins a few yards below the surface, where vibrations might damage brick buildings in Pioneer Square if not controlled well. Bertha then dives a mere 20 to 40 feet below pilings that support the 60-year-old waterfront viaduct.
Meantime, the machine operators will still be getting a feel for how Bertha handles.
No wonder the work will proceed at just 6 feet per day at the outset.
“The part that everybody is the most sensitive about, and the most concerned about, is going under the Alaskan Way Viaduct when we start, because everything is so tight,” said Lynn Peterson, secretary of the state Department of Transportation (WSDOT).
Awed by the sophisticated parts, Peterson said she feels as if she’s watching an engineering documentary — and in fact, an IMAX crew has been here to take footage.
WSDOT plans to finish the $2 billion, four-lane tunnel by late 2015, with funding mostly from gas taxes. Toll rates have not been set by state officials and an advisory group, who seem at a loss as to how to raise $600 million for construction and operations without causing drivers to divert and clog nearby streets.
Seattle Mayor Mike McGinn for years has objected to spending huge sums to serve carbon-spewing automobiles. He skipped Saturday’s ceremony to campaign in West Seattle for re-election, then spoke downtown at a Trayvon Martin civil-rights rally.
Plan of attack
The political world seems distant within the machine, where welders shout and smoke, Japanese control-room technicians sweat, and an alarm on the hydraulic arms chimes like an ice-cream truck.
The machine’s kahuna is Gregory Hauser, a 66-year-old engineer, veteran of 35 projects and deputy project manager for contractor Seattle Tunnel Partners. He helped lead Brightwater to the finish line after two drills eroded in abrasive dirt and got stuck.
“This is the highlight, it really is, just because it’s so big,” he said, after crawling out of the cutter’s backside and climbing a double staircase. “Nobody’s ever done anything like this before. We’re going to tunnel under downtown Seattle and build a highway as we go. It’s an extremely challenging project.”
The cylindrical machine is packed with hoses, gauges and head-smacking catwalks, like a submarine, which it is. Bertha will withstand more than four times atmospheric
pressure when it bottoms at 100 feet below sea level shortly after passing the viaduct.
There’s a control room, lunchroom and strategy room. And even hyperbaric capsules to transport workers, trained like deep-sea divers, into high-pressure areas immediately in front of and behind the cutter head. The divers will make inspections, replace worn parts and troubleshoot if the machine gets stuck.
“It’s a little city,” says Bob Donegan, president of Ivar’s and a follower of the project.
As the machine advances, arc-shaped concrete segments will be delivered from the rear and set in place by two vacuum arms to form a succession of giant rings. Once a ring is completed, 56 hydraulic rams within the machine will push against the front rim of the ring to propel Bertha ahead, 6 feet at a time. The 56 thrusters, also called jacks, are the sole means of steering the colossal cylinder.
The drill’s waterfront route will be cladded by rows of thick concrete pilings, on the bay and inland sides. The roof of this protective box includes a 400-foot-long slab of concrete exerting downward pressure, so groundwater cannot float the tunnel upward. Concrete grout injected into the soil should make it more stable.
The viaduct has been wrapped in carbon fiber, painted gray and reinforced by steel rods in the soil.
WSDOT might close traffic for a few days as a precaution against what it calls a tiny risk of vibration-loosened fragments falling on motorists.
Because the Highway 99 precautions are thorough, Hauser insists: “Brightwater was tougher than that.” The sewer route burrowed under railroad tracks just 80 feet from the launch site, next to Puget Sound at the King-Snohomish county line.
Oatmeal, not stew
Once Bertha moves past the viaduct, “the soil gets better and deep as we go” because it has been compressed by multiple glacial flows, said project manager Chris Dixon.
However, Seattle-area dirt is abrasive enough to erode cutting teeth. Therefore, polymers, grout and soap will be carried aboard in tanks. The soap will make the soil slippery so cutting surfaces last longer. Wherever groundwater intrudes, polymers will be squirted into the soil to stiffen the dirt flowing into the machine — so the texture is consistent and easy to measure.
“We want a paste or a cream, like stiff oatmeal,” says Hauser. “I don’t want beef stew.”
Measurement errors can lead to voids, one of which almost swallowed a Beacon Hill home during light-rail tunneling. Scales to measure weight and lasers to measure volume are meant to ensure that excessive dirt won’t tumble into Bertha from overhead.
Above ground, $20 million is being spent for 700 high-tech devices to monitor streets and buildings, and another $20 million to brace the century-old Western Building.
Over the 1.7-mile dig, an estimated 9 tons of steel will flake off the drill.
There are more than 600 cutting tools: large teeth to chew the soil, discs to crack boulders, smaller teeth to scrape and shape the dirt. More than 30 of the tools can be replaced by workers who crawl through the spokes. Other repairs require those trained like deep-sea divers to venture into high-pressure areas in front of and behind the cutting face.
discs, from the Robbins Co., are protected by a unique seal, and grease inside the discs will be pressurized so water and sand can’t seep into the bearings, said Dick Robbins, of Seattle, a retired company board member and inventor.
Robbins says abrasion is a worry. “I think they are experienced enough to avoid that problem, but we don’t know. There’s some risk,” he said. Robbins notes that compared with Brightwater, the huge Highway 99 drill “is a much bigger diameter, which of course makes it less stable for the same geology.”
But he also said Hitachi and lead tunnel contractor Dragados, which successfully built a huge highway tunnel in Madrid, understand the terrain. Once the drill hits so-called virgin soil beyond the viaduct, he predicts the machine “should operate without any hiccups.”
Mike Lindblom: 206-515-5631 or firstname.lastname@example.org