Checking in on Bertha

Last month, I noted the second anniversary of the day “Bertha,” the deep bore tunneling machine that was supposed to carve out a tunnel beneath downtown Seattle that is to replace the decrepit and dangerous Alaskan Way viaduct, ceased drilling barely 10% of the way through the project. As I noted with some skepticism then, tunneling was scheduled to resume in late December after a 2+ year delay.

The good news is that my pessimism regarding the late December start date proved unwarranted–drilling did in fact resume, and over the last few weeks around 200 feet have been added to the 1000 or so feet that had been completed in 2013. The bad news, unsurprisingly, is considerably worse: tunneling was abruptly halted today by order of Governor Jay Inslee. The reason?

Bertha began tunneling again Tuesday evening. About two hours after the machine started boring again, a sinkhole developed in its wake — about 100 feet south of the machine’s current position. The sinkhole occurred in an area where crews mined last week.

The sinkhole developed in the work zone behind Bertha’s path at South Main Street, which is about 35 feet north of the access pit.

WSDOT has not stated how large the sinkhole was, but did say that tunnel crews have filled it in with 250 cubic yards of concrete.

In the first round of troubles, WSDOT and STP (the contractors, “Seattle Tunnel Partners”) did a pretty good job of presenting a united front. Now that we’ve entered the “everyone sues everyone” phase, such niceties have been abandoned:

In its announcement detailing the sinkhole, WSDOT said that certain protocols, which Seattle Tunnel Partners used for enhanced monitoring, were only used during the first 1,000 feet of excavation. WSDOT said that it is disappointed that those protocols were not being used after Bertha began boring again in December.

Five and a half years ago, just before the Seattle City Council give its stamp of approval to this disastrous plan, Dominic Holden published an article entitled “What could go wrong.” The second of that article on boring machines getting stuck has already more or less come to fruition. Holden also foresaw our current difficulty:

The ground caves in

Because we’re dealing with loose soil, there is a chance that the ground could cave in behind the tunneling machine. This isn’t as likely as a TBM breaking down, but it can and does happen. In fact, it happened last year north of Seattle on the Brightwater project. A 30-foot-wide, 15-foot-deep sinkhole swallowed up Pauline Chihara’s driveway in Kenmore. Tom and Jan Glithero, who live above another one of the Brightwater tunnels in Bothell, found cracks in the brickwork in their home, their patio, and their driveway—all attributed to settling caused by the tunnel’s excavation underneath the couple’s home.

In 2003, a sinkhole opened up near a tunnel being bored in London, and people had to evacuate their homes. On March 3, 2009, a tunnel collapsed in Cologne, consuming the city’s historical archives building and killing two people.

“I’ve seen overexcavations open up 300-meter tall caverns over the TBM, and all that dirt fell right on the machine,” John Turner, chief engineer of TBM builder the Robbins Company, told Machine Design in 2001. “And the cave-in can go all the way to the surface, which is a real disaster.” In the same article, Marco Giorelli, a product manager for another TBM builder, said, “Overexcavations can be particularly harmful in cities… They lead to settlement, and it doesn’t take much settling to damage buildings.”

The loose soil in downtown Seattle doesn’t have driveways or single-family homes sitting on top of it. It has the historic buildings in Pioneer Square, new condo towers and hotels, and the tallest buildings in the state.

It’s worth noting here that while the project doesn’t seem lucky, both the location of the machine getting stuck and the sinkhole are extraordinarily lucky, given that nothing of significance was blocking the rescue tunnel/on top of the sinkhole. Looking at Bertha’s path, it’s going to take us under some of the oldest and densest parts of downtown Seattle. As bad as this project has gone, it could have been (and may still be) much worse.

The initial plan was to stop long enough to make sure this particular sinkhole wasn’t an immediate threat to the project or any structures (the vacant location is a stroke of luck, given the roads and buildings the tunnel is theoretically about to go under) and plough ahead. Inslee wants to know *why* this happened, and assurances it won’t happen again, before tunneling resumes. It’s far from clear to me STP is up to this task, and whether such assurances can plausibly be made at all–STP and WSDOT’s public statements about Bertha’s problems have historically amounted to little more than vague assurances that everything will be fine and a whole lot of ¯\_(ツ)_/¯.

As a reminder, unlike the many boondoggle transit projects such as the big dig, this tunnel would have been a staggering waste of money had it been on time and under budget: it would be useless for most viaduct users today as it contains no downtown exits. It’s doubling down on a car-centric transit future (it’s difficult to imagine any public transit applications for the tunnel, except perhaps a few specialized peak-only express routes) at a time when the region’s voters have, sensibly, made clear that they want to invest in public transportation. The foolishness of the project, and the extraordinary risks it entailed, were well understood before it began. I’ve long speculated that one of the possible end-games for this project is that, if the public turns on it with sufficient fury by the summer or early fall of 2016 and Inslee’s reelection campaign isn’t going well, he advocates abandoning the project in his effort to get re-elected. I still consider this scenario a longshot for a variety of reasons, but it’s more likely than is was 72 hours ago.