December has not been kind to Seattle's enormous tunneling project. And not just this December.

A year ago this month, North America's largest tunnel-boring machine got stuck just 10 percent of the way through a 1.7-mile-long dig under downtown Seattle. Throughout 2014, engineers have been plugging away on an ambitious plan, outlined in a Popular Mechanics feature, to free the mechanical marvel and get the project going again.

But today, Bertha remains stuck under the city. And according to an update from The New York Times, crews monitoring the project to free the machine have noticed something alarming: one inch worth of settling in the downtown district under which Bertha now sits.

"A whole block just went down an inch," said Todd Trepanier, the administrator of the project for the State Department of Transportation, at Monday's City Council hearing. "We don't like an inch."

The Rescue

The effort to replace the aging and elevated Alaskan Way Viaduct in downtown Seattle involved a decade of planning that finally settled on digging a tunnel under the city. Bertha, a 57.5-foot-diameter tunnel-boring machine, was built in Japan and shipped over for the job. Tunneling began in earnest on July 30, 2013.

By December, it had ground to a halt.

The first portion of the dig was routine, easy ground for Bertha to cut through as it got its teeth dirty. But just more than 1,000 feet into the dig, the machine slowed. Seattle Tunnel Partners, the contractor group running the project, thought they had hit an obstruction and sent divers in through Bertha to take a look. They found nothing.

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Instead, investigators eventually concluded that Bertha was overheating—that grime and gunk had gotten past bearing seals, entered the machine, and muddied the operation. Engineers still aren't sure why all this happened to the 326-foot-long machine, but they decided they had replace not only the seals but also the $5 million main bearing.

But just getting to Bertha, which sat more than 60 feet below downtown Seattle near the stadium district and the waterfront, posed a serious problem. Crews could go through the painstaking, time-sucking process of disassembling the machine from behind to make the fixes, but instead chose to dig a 120-foot-deep access pit in front of Bertha.

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The Worries

When construction of the pit started in October, planners said they could have Bertha fixed and tunneling again by April 2015, about 16 months after the initial stoppage. That will still put the project well behind its original timetable, which aimed to have this main 1.7-mile portion of the 2-mile tunnel open by the end of 2015. But at least Bertha would be moving again.

No such luck: The access pit being dug to repair the machine is on hold about 80 feet into its construction after settling was found in the area around the job site. Workers discovered one inch worth of differential settlement, which is especially worrisome. That's when the ground settles unevenly over an area, making it more unpredictable than if they had seen uniform settling.

To keep the access pit and tunnel from collapsing, crews have used pumps to send millions of gallons of water away from the site so that it doesn't stay in the soil and add to the pressure. While Seattle Tunnel Partners will work with a geostructural designer to figure out how to stop dewatering without causing major shifts in the groundwater pressure, crews will dig another three feet of the access pit and reassess the situation.

The Washington State Department of Transportation reports that no major structural issues have been found in the area, including to the Alaskan Way Viaduct. But The New York Times reports that the settling has affected about 30 businesses in the Pioneer Square area above the tunnel-borer's current location, with some reporting new cracks in their basements and foundations.

Decembers haven't been kind to Bertha. But right now, there isn't much to look forward to in January, either.

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