Two Consultants Focus on Deep-Bore Tunnel Risks, Not Rewards

The tunnel's southern approach, or, "Acres of Asphalt"

This week, two consultants gave briefings on the deep-bore tunnel planned to replace the Alaskan Way Viaduct: John Newby, P.E., hired by Seattle's City Council, and Dr. Thom L. Neff, hired by Mayor McGinn (video here). Neither man said it would be easy, and neither cared to back up Gov. Gregoire's claim that there will be no cost overruns period.

But apparently it was not within the scope of their inquiry to assess how worthwhile the project is, given the risks. What is the bang for the multi-billion-dollar buck? How does this project's cost/benefit compare with other transportation projects facing the state? Crosscut wants a tunnel vote, but as much as I am dubious about the tunnel project, and despite writing about it for months, I still don't have the information needed for a baseline comparison.

Some very risky projects are worth it. Some aren't. I still maintain that Seattle's decade-long deadlock on the Viaduct's replacement simply indicates that a truly fair, useful, simple solution hasn't been arrived at--largely because leadership insists on "replacing" the Viaduct, rather than better serving the different populations who rely on it. Instead, we're offered a 1.7-mile underground bypass estimated to cost almost $2 billion before anything goes wrong.

"When things go seriously wrong with urban tunnels, the consequences can be significant, leading to long delays, large cost overruns, and extensive 3rd party damages," says Newby's report. Publicola clarifies that--just so there's no confusion--the City Council was informed that there's a 40 percent chance of cost overruns on the $1.96 billion tunnel itself, though the odds incline toward a total of not more than $2.25 billion.

Newby certainly knows firsthand the risks of tunneling; his firm CDM are geotechnical consultants on King County's plagued Brightwater sewage conveyance project. (Here they are discussing in advance how you need to have options besides rescue shafts, given the expense.) "Seattle area glacially consolidated soils have caused significant wear to TBM cutterheads and tools," his report notes. ("Significant" as in "irreparable in situ," in one case that springs to mind. Options? "As of May 1, we have no way to remove it and are still working on a plan," said King County's project manager.)

Neff, from Ockham Konsült, has an ill-fated mega project of his own to spur his sense of risk: Boston's Big Dig. He was an executive with Parsons Brinckerhoff during that project, and he says Seattle's tunnel is even more complex.

"He cited sticky clays, flowing sands, abrasive materials and boulders up to eight feet in diameter that stand in the way, the fact that the tunnel would be bored below sea level, and that the tunnel, at 54 feet in diameter, would be the world's largest of its kind," sums up the West Seattle Herald.

Neff's ultimate "It's risky!" point seems to be that, if you have a situation with a firm not-one-penny-more cap on funding, prudence would dictate that you not try to dig the world's largest-diameter deep-bore tunnel in an area that, geologically, has proven (twice) unfriendly to much smaller deep-bore tunneling machines.

On WSDOT's cost modeling, Seattlepi.com quotes Neff saying: "If you look at the documents, this model ... is unbelievably complicated and it has ample opportunity to inject personal judgment into it when you create the model. They ran something like 10,000 iterations of it until they came up with a number they liked."

Already the field of four deep-bore tunnel builders has dropped to two, with the strangely below-radar departure of the AWV Joint Venture group. This is concerning because WSDOT has essentially told the teams to design the tunnel for a given cost, and Kiewit's statement that "The current contract model and our business model are not compatible," hints at an inability or unwillingness to shoulder that responsibility.