Alaskan Way Viaduct replacement program administrator Todd Trepanier told reporters today that the public has no reason to worry about news that Seattle Tunnel Partners' work inspecting the stalled tunnel-boring machine had caused the viaduct to sink, or settle, as much as four-tenths of an inch. (The exact amount of settlement, Trepanier said, is "more complex than just one number," because the viaduct can settle both vertically and horizontally, among other factors.)
The settlement resulted from STP's work doing multiple "hyperbaric interventions," filling a protective membrane around the front of the tunnel boring machine and filling it with compressed air so workers could go inside and try to figure out what was stopping the machine. (Turns out it was a set of damaged seals around the machine's main bearing.)
Trepanier said the state's contract with STP anticipated some tunnel settlement.
"The work that they've done has settled it slightly, just as was anticipated by their designs, but ... that settlement does not endanger the viaduct [and] does not move the viaduct closer to closure. This was settlement that was anticipated and we knew it would happen as part of the tunnel activities."
Trepanier said the tunneling team has "restrengthened" and "reshored up" the viaduct as part of the construction process "to ensure that it can stay open and be safe for traffic." Barring some catastrophic event like a major earthquake—at which point "the viaduct settlement will be the least of our worries"—Trepanier said "there is no indication that we are at a point, nor could we predict a point, that it would become unsafe to use the viaduct. ... It's just not going to happen."
On a separate note, I asked Trepanier about Metro's pledge to continue to fund Metro service on the viaduct through 2015. Currently, WSDOT says it plans to open the tunnel in 2016. If that date gets pushed back due to construction delays, what happens to that mitigation funding, which pays for some 40,000 hours of Metro transit service?
"The idea was that this transit funding is for construction mitigation, and it is something that DOT has always supported and felt it was beneficial to have those transit operations in place during the disruption that was happening during construction," Trepanier said. If construction drags on past the current open date, he said, "There's not a contingency plan, but those issues would be dealt with at that time. ... An extension is something that, if [a delay] started to happen, that would be part of the conversation.