What do you do if you're operating the world's biggest tunneling machine and something goes wrong? You're digging along, everything fine, the machine's five-story maw about to chew beneath the skyscrapers of one of the great American cities. Then suddenly one day things are not so fine. Bertha—that's her name, in honor of Seattle's first woman mayor, Bertha Knight Landes—hits something. A few days later her temperature starts rising. Not good. Then her cutting head stops spinning.

Now what? What do you do when the world's largest tunneling machine is, essentially, stuck in the mud? Bertha is 60 feet under the earth, and you're on the surface watching a squirmy public swap rumors of cost and delay on the $1.35 billion tunnel component of an even larger transportation project, and the naysayers are howling: Just you watch, Bertha will be abandoned like an overheated mole, boondoggle to end all boondoggles. Because, don't forget, when you're boring the world's largest tunnel, everything is bigger—not just the machine and the hole and the outsize hopes but the worries too. The cynicism.

What do you do?

Here's what you do: You try to tune out the media. You shrug off the peanut gallery's spitballs. You put off the finger-pointing and the lawsuits for now; that's what the lawyers are paid for afterward. You do the only thing you can do. You put your head down and you think big, one more time. You figure out how to reach Bertha and get her moving again.

This is a rescue story.

Ask a Seattleite why he likes it here and he'll invoke the things we Seattleites always say: good fish. Better coffee. White sails on the blue water of Puget Sound. Never high on anybody's list is the Alaskan Way Viaduct. For 61 years the elevated double-decker freeway that slices along the waterfront has been the city's grim, gray mule, carrying roughly one-third of Seattle's north–south traffic while effectively divorcing the city from its waterfront, as so many other highways have done around the nation—from New York City's FDR Drive to Boston's Interstate 93 before the Big Dig buried it.

In 2001 a magnitude 6.8 earthquake rattled Seattle, cracking the aging viaduct. As years passed and the road deteriorated, the city argued about what to do. Finally, in 2009 local and state leaders decided: the viaduct would fall. In its place a waterfront renaissance would bloom as 26 blocks along Elliott Bay rejoined the city. James Corner Field Operations, visionary of the acclaimed High Line project in Manhattan, was hired to imagine a string of walkways, parks, public piers, bike paths, beaches—even a swimming pool on a barge—that would knit the city's core and its shoreline together and transform the place into an urban waterfront to rival those of Sydney, Copenhagen, Vancouver.

The costliest and most complicated puzzle piece—the one that would make all of this possible—would also be one of the least visible. A 2-mile tunnel would replace the hulking viaduct. The tunnel would whisk traffic underground from the Seattle Seahawks' stadium, just south of downtown's high-rises, north to the Space Needle and South Lake Union.

Seattle's tunnel wouldn't be very long—just 1.7 miles of it bored through the earth—but it couldn't be just any tunnel. It needed to be big enough to hold four lanes of traffic across two decks, with cars traveling at highway speeds. It would have to dive deep, more than 200 feet below downtown's heart, to avoid disturbing the city's skyscrapers and old buildings. The machine would have to be wily enough to dig through Seattle's funky soils, everything from glacial till to pudding, the latter a legacy of early city fathers, who flattened the lumpy pioneer town into the salt marshes to create the modern city by the sound.

The requirements emerged: Bertha's cutterhead—her face—would be 57½ feet across, as tall as the viaduct she was replacing. She would have hundreds of teeth to chew with. She'd digest the muck she chewed and then build the tunnel behind her as she worked, so she would be 326 feet long, as long as a home run over the right-field fence at nearby Safeco Field. She would weigh as much as the Eiffel Tower and would use enough power to light a town of 30,000 people. She'd be able to generate so much thrust—44,000 tons—she could send 13 space shuttles into orbit. And, of course, she'd be burly, because by the time she burrowed through the subterranean darkness and emerged on the other side she would have shed 9 tons of solid steel.

Bertha would be all of these things. She would be the biggest tunnel-boring machine ever built.

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And yet, for all her complex engineering, here she sits, a thorn in the side of the Washington State Department of Transportation. A huge accomplishment turned even huger headache. The biggest tunnel-boring machine ever to get stuck under Seattle.

More than six months after Bertha had stopped her daily tunneling, I headed down to Seattle's historic Pioneer Square neighborhood to see her sulking in her hole; I wanted to see the plans that were afoot to get her moving again. Just to the west nodded the dromedary cranes of Seattle's port. Nearly above me loomed the viaduct, its concrete the stained color of the city's November skies. Rusting rebar showed through it like bones. Bertha had stopped tunneling just short of the viaduct's first pillars, with Seattle's first buildings just a few feet beyond that. It was Friday afternoon, and the viaduct throbbed with the traffic of people sneaking off to early weekends. You had to shout.

Beneath the viaduct I met the tunnel's project manager, Chris Dixon. Dixon is 61 and gray-haired, with a tucked upper lip that suggests a man accustomed to keeping his words and his temper close. He wore the uniform of job-site managers everywhere—steel-toed boots, pressed khaki work shirt, blue jeans a shade darker than his eyes. A white hard hat said SEATTLE TUNNEL PARTNERS, the moniker for the team of large-construction firm Tutor Perini and tunneling specialist Dragados that together won the contract to build the tunnel. A vice president of operations at Tutor Perini, Dixon is a lifelong major-project guy. I asked him where home is. "Wherever we are at the time," he said. "We have no roots anywhere. My wife's Australian. My first job was as a 16-year-old tunnel laborer on a tunnel job in Australia." He rattled off some of the places he's worked. Albania. The Sultanate of Oman. California, for L.A.'s Metro Red Line Subway Project, and the BART extension to San Jose.

We walked onto a bridge spanning a broad scoop in the earth. The scoop sloped into a yawning, five-story hole, like the entrance to a burrow of some animal you weren't sure you wanted to see up close. There were stacks of shovels and, beneath the thrum of the viaduct, the sound of trickling water. This, Dixon explained, was Bertha's launch pit, where the whole thing started.

Bertha was built by heavy-machine-maker Hitachi Zosen of Japan, which had constructed more than 1,300 tunneling machines before her. Once she steamed into Seattle in 41 pieces in April 2013, her five-story, Sonics-green cutterhead became recognized around town, a local celebrity. She had her own Twitter feed, sending out cheeky messages about her progress: "The specialized truck that's moving me has 96 axles and nearly 800 tires. It has won exactly zero races," she tweeted as she was unloaded. A divided city leaned in, grew more excited. A kid dressed as Bertha for Halloween. A woman made a giant meatloaf shaped like her, with workers fashioned out of Lit'l Smokies sausages. Once Bertha was assembled and positioned in the launch pit, 5,000 people came out to wish her well. The governor spoke. He and former governor Christine Gregoire cracked a bottle of wine against her steel, and a bottle of sake. "I should say something profound, something Neil Armstrong-ish," Bertha tweeted. "Fortunately, I'm out of characters. Let's dig." On July 30, 2013, she got to work.

The Rescue

Bryan Christie Design

(Illustration by Bryan Christie Design)

A look at what it will take to snatch Bertha from the depths.

1. This summer Seattle Tunnel Partners sank 73 concrete pillars in a huge ring in front of Bertha's face. Workers then excavated the hole until it was deep enough to swallow an 11-story building.

2. Though she's running hot, Bertha can still move. Soon she will chew through the front of the protective wall until her head rests on a concrete cradle in the rescue pit.

3. Finally, a custom crane called a modular lift tower will raise Bertha's 2,000-ton face, tilt it, and set it down. Workers will replace Bertha's bearing assembly and add 86 more tons of steel ribs and plates.

Ian Allen

To understand how a tunnel-boring machine works, think of an earthworm. The worm eats. It pushes forward. It expels. This is Bertha in a nutshell. As her 886-ton cutterhead revolves at about one rotation per minute, 260 spinning and stationary teeth chew the soil before her. Nozzles on her cutterhead spray saliva-like conditioners that transform the soil into the consistency of toothpaste. The soil is pushed through the large, mouthlike holes in her face. Then this chewed-up earth—it's officially called tunnel muck by engineers—enters a chamber where it's stirred and conditioned still more.

Next comes digestion: High pressure deep in a tunnel forces the muck up Bertha's gullet, a massive ribbon screw that works like an Archimedes' screw, but whose shape ("It's like a Slinky," Dixon said) allows it to swallow boulders up to 3 feet wide. The screw carries the muck farther back into Bertha, until it's deposited in her "intestines": a giant conveyor belt that reaches out of the tunnel and dumps its waste onto a barge on Puget Sound. The conveyor belt will grow as Bertha digs until it eventually stretches some 9,000 feet to the tunnel's end. Without this system the project would need an average of 200 dump trucks per day rumbling through downtown to carry away all the muck that Bertha digests.

Dixon climbed down a ladder made of 2 x 4s and stood in the tunnel's mouth. It soared—a five-story-tall tube bending slightly into the earth. Lining the tube were the precast concrete pieces—18 tons apiece—that Bertha lifts into place, forming consecutive rings to build the tunnel behind her. Dixon pointed high above us, where initial work on the upper-deck roadway was about to begin despite Bertha's pause. "The only thing that's stopped on the job is the actual tunnel boring itself," he said. "Everything else is going ahead full speed." Nearby, for instance, work had been reshuffled to begin on the tunnel's "brain," a multistory subterranean building that will house the controls for signals, airflow, sprinklers, and the like.

We walked nearly a quarter-mile down the already-finished tunnel and climbed into Bertha herself. There the scene was pure industrial gothic. It was close and dim. There were steel catwalks and steel railings, and steel pipes going to and from unknown places. The air smelled of earth and grease and hard work. Even at rest the machine felt busy. We climbed higher and Dixon pointed out two man-locks: Down in a tunnel, soil and water team up to increase the air pressure at the front of the machine, just as a diver experiences increasing pressure as he descends. Whenever work has to be done at the very front of the tunnel-boring machine, workmen can't stay long, and they must decompress afterward.

Finally we halted at the operator's cabin—the control room. The operator sat before a large console. It was spare and beige with analog gauges and big, green LED readouts, like something borrowed from a Cold War missile silo. On the control panel before us he pointed out several monitors, including ones that keep tabs on the tunnel-boring machine's temperature. It seemed a great place to ask about Bertha's recent woes.

On Dec. 3 of last year Bertha hit something. It was a pipe, an 8-inch steel well casing sunk to monitor movement of groundwater. Huh, the tunnel folks thought. They noted it and kept tunneling. Three days later Bertha's temperature rose. Then she started requiring more thrust to advance, more torque to turn the cutterhead, as if something was in the way.

There's disagreement over whether the pipe incident ultimately mattered or whether it was just coincidence; workers plucked a piece of the casing from her maw like a shard of toothpick. But what was obstructing her, the tunnelers soon realized, might be dirt itself: While Bertha can gnaw through concrete, earth of the wrong consistency can interfere with her ability to spin. By sending workers into the high-pressure environment in front of Bertha's face, using those man- locks, they cleared her mouth. But when they got her moving in late January, she ran hot again. "What we didn't realize at that time," Dixon said as we stood closer to her cutterhead, "was the amount of damage that the bearing seals had suffered."

In Bertha's neck is a bearing similar to the bearing on the axle of your car, only much, much larger. As in a car bearing, the working parts are sealed to keep lubricants inside while keeping out contaminants that can cause friction. It's particularly crucial that this system work flawlessly in a tunnel-boring machine, which is surrounded by intense pressure that can force grit into the bits that need to spin freely. When workers investigated, they found that the seals protecting the main bearing had been damaged. Contaminants had gotten deep inside.

This was not good. Bertha had dug only 1,023 feet. She had some 8,000 feet to go. Every foot she drilled was another foot deeper under the city, another foot farther from easy aid.

All was not lost, though. She was still near home. "To be honest, if Bertha was going to break down anywhere, that's about the best possible place it could have happened on the job—they'll get her fixed," Amanda Foley, North American editor of Tunnelling Journal, told me in an email.

Yes, repairing her would be a world-class pain in the ass. But it was better than getting stranded under Pike Place Market.

Dixon and I emerged squinting into daylight and walked north. A half-year had passed since daily tunneling had ceased. Around town people were wondering what was going on. Some fretted. Others gloated. The week of my visit, the alt-weekly The Stranger, which had long hated the notion of the pricey project, even suggested that "our money-sucking tunnel" might be abandoned and was soliciting ideas for its second life (mystery dinner theater! giant sushi conveyor belt!). For her part, Bertha no longer seemed herself. Her tweets had lost their playfulness; they were curt, businesslike, even a smidge defensive. "There's still a lot of tunnel-related work happening," she insisted, despite her predicament.

Dixon and I walked until we were past the tunnel. The viaduct loomed just ahead. While the launch pit had been almost sleepy, here was total noise: Cement trucks spun. Workers banged sledgehammers. Welders drizzled sparks. This was ground zero of the repair effort.

Dixon explained what we were witnessing. In the open ground in front of Bertha workers were creating a ring of 73 enormous, connected concrete pillars. Once finished, he explained, the crew would spend the rest of the summer excavating that ring to create a shaft wide and deep enough to swallow an 11-story building—a vertical rescue tunnel.

True to form, even this effort is Brobdingnagian in scale. In October Bertha will fire up her engines again and chew through the front of that protective wall until her head rests on a concrete cradle that workers have molded on the pit's floor. There workers will gradually decapitate her.

Next comes a bit of heavyweight ballet: A Texas-based company named Mammoet, which specializes in moving the massive—salvaging ferries from the seafloor, lifting power-plant reactors into place—will trundle a modular lift tower (a sort of custom crane) over the pit. The machine will hoist Bertha's entire cutterhead assembly—all 2,000 tons—in a single dead lift, tilt her face 90 degrees in midair, and set it down beside Elliott Bay, just like lifting the motor out of a car to work on it in your driveway.

By then a ship from Osaka, Japan, will have arrived with new parts, including a shiny new bearing assembly—an elaborate improvement, Dixon said, containing seven seals and several different chambers, with opportunities for grease to be injected at multiple points in the system.

While aboveground Bertha will be disassembled and fixed and get a bit of a face-lift, too, including widened mouths on her cutterhead to make her a meaner eating machine, and 216 steel ribs and plates added to her head as reinforcement. "We want them to get it running," Dixon said, "and assure us with 100 percent confidence that it can complete the remaining 8,000 feet."

In November everything will be pieced back together like an Ikea chest of drawers and returned to the ground in reverse order—without leaving any 1-ton screws lying about on the surface. If all goes well, Bertha will be tunneling again by early March. Though "it's too early to say whether they're going to make their schedule or not," Matt Preedy, deputy program administrator for the Washington State DOT's Alaskan Way Viaduct Replacement Program, said, the tunnel could open in November 2016, just 11 months later than originally promised.

Is all of this effort—an 11-story pit, a snatch from the depths—really necessary, I asked Dixon. Couldn't the tunnel partners make the repairs by, say, using the tunnel?

"It can be done," Dixon replied—and that's what would happen if Bertha had gone kaput deep under Seattle. But as he told me later, "The repairs would be much more complicated and expensive." You'd have to disconnect Bertha's entire body, back it out of the tunnel, make the repairs, then reattach everything.

At heart, he said, it's "just an engineering problem. Certainly things have occurred on other projects—not major catastrophes, but things that you think, now we're dead in the water. But you always find a way to work through those things and complete the project."

Harder than engineering, Dixon said, is managing human expectations. "There's three things that are really critical on a major project in an urban environment in the U.S.: politics, the media, and the community. I've always just focused on controlling the things that I can control," he said. "I'm known as having a very even temperament."

He also has reason to remain calm. Bertha is still under warranty. And someone will eventually shoulder the (many) additional costs of the 16-month delay. The lawyers will sort it out, if it comes to that. "It's to be determined," Dixon said coyly, smiling.

Beyond the lengthened schedule, however, a larger clock is ticking. There is that small matter of the earthquake that ravaged the viaduct in 2001. For now the road is safe, but in 2007 a state study reported there was a one-in-10 chance another viaduct-threatening earthquake would occur in the next decade. If that happens, Seattle could have a real problem on its hands. So long as it doesn't, Bertha can spare a few months to recuperate.

Dixon can't think about all that now. For the next five months, possibly the most crucial period in the entire project, he can focus only on rescuing Bertha—getting her out of her purgatory and back to chewing her way under Seattle. Which is why, even though at 4 pm the viaduct above us was already humming with folks heading home for the evening, Dixon said goodbye to me, hung up his orange vest, and drove back to the office.

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