(TOPLINES: State insists Viaduct safe. Council wants to know specifics of what would make it unsafe. State says it’s up to tunnel contractor to figure out what happens next)
(Screengrab substituted for video window after meeting; will add archived video when available)
2:47 PM: The City Council regularly gets briefed on the Alaskan Way Viaduct Replacement Project, but with the disclosures of the past few days, the meeting under way now takes on extra weight. Watch in the video window above (click “play” for the live stream); we’ll note key points as it goes.
Regarding the “settling,” WSDOT officials say it does seem to have coincided with the “dewatering” process, which they explain involves a series of wells, to reduce the pressure as the contractor dug further down toward 120 feet in depth. This new settling, it’s explained, was detected by a wider swing in the survey area revealing “deep benchmarks” had settled – where they weren’t supposed to. “Local” settling is what they WERE expecting. But adding that to the “deep benchmark” settling, they came up with the inch of settling reported last Friday.
**AS-IT-HAPPENED COVERAGE CONTINUES AFTER THE JUMP**
They needed to figure out “what is really going on here, is it really tied to these dewatering wells?” so that’s why they did extra surveying over the weekend. WSDOT says that as they analyzed data over the weekend, they noted that “the Viaduct has experienced some settlement but it’s very uniform in nature and does not represent any form of safety threat for the Viaduct” but in the assessment of the “deep benchmark” settling, they could not confirm it was absolutely related to the dewatering wells, which have been in action for about three weeks. They’ve reiterated several times that they don’t believe there’s any safety risk.
As for shutting the wells off – “you don’t just flip a switch” to do that, it’s been explained, because if you did, you could damage nearby buildings or the pit itself.
2:59 PM: About 30 buildings in the “influence zone” have the one-inch settling situation, it’s just been explained. And they’re going to “kick up the surveying” beyond that zone. Now the briefing is moving to WSDOT’s Tim Moore, to speak to structural safety – “he knows the Viaduct better than anyone.” He says he’s been with WSDOT’s bridge office for more than 30 years. He reminds the council that the project is scheduled to tunnel underneath The Viaduct at some point once it restarts.
He talks about monitoring, saying they’ve surveyed over the east and west “gutter lines” since the 2001 earthquake, and did another such survey last Sunday morning “so we know how this structure has behaved (since then).” About the “differential settlement” – the uneven settlement that’s of concern,” which he describes as the “key component of whether this structure is going to see distress” – he says they’re not seeing that kind of distress so far.
They are surveying key points daily in a manner that can be done without closing travel lanes, WSDOT officials tell the council. Now Councilmember Jean Godden asks about the discrepancy between what was said long ago regarding 6″ settlement requiring shutting it down, and 6″ total settlement now being described as NOT requiring that. “Some of those large settlements in the past have been taken out of the picture …” because of strengthening, she is told. “It’s kind of like a start over.”
“I don’t think Viaduct closure is imminent,” Moore says.
Councilmember Sally Clark voices concern about settlement happening on one end and not the other, and won’t there be some “tugging”? Moore explains it’s really three spans that “act independently of each other.”
So what if you stop pumping the water and it comes back in? asks Councilmember Sally Bagshaw. A consultant takes that one on. He says most of the deep settlement seem to be happening “down in the glacial soils in the vicinity of where the water is being taken out.” He says it’s a “spring kind of compression” that might also rebound. “So what about the buildings on the surface?” she asks, if it’s “condensing and expanding, condensing and expanding.” They think “there’s a very good chance” the buildings will suffer “no lasting effects,” but they’re checking to be sure.
Councilmember Mike O’Brien notes that the 6″-settlement threshold is the only one they or we have ever heard, so if that’s not valid any more, WSDOT needs to articulate some better way for us to understand what *is* the safety threshold.
“Case by case,” he is told, “obtaining the information continually and timely” – assessing structures. “What can happen to a structure (then) and what cannot?” O’Brien presses.
Moore is asked for a scenario “that would lead you to concern,” then, to answer that. He mentions “fairly significant” structural cracks that are not getting in the way of the Viaduct to safely carry traffic, but would reduce its originally expected 75-year life span – though that’s beyond the time frame expected for it to be taken down. (It’s half a century old already.)
O’Brien is still pressing for clearer details on what would cause WSDOT to say it’s not safe any more. He wants to know specifics. “It’s really dependent on some characteristics … if it’s a slow settlement, the concrete can … dissipate some of that over time,” Moore explains. “(So far) we haven’t seen a huge buildup of strain in the reinforcing steel.” He reiterates, the Viaduct won’t make it to its originally planned 75-year life. And O’Brien still wants to know, what would push it over the limit? Moore says he just doesn’t have something specific to say in response.
Councilmember Sally Clark now points a question at SDOT director Scott Kubly, wondering who’s checking the state’s work as the plans for digging the hole are revised, and so on. Kubly says that’s a good question and backtracks to explain that Mayor Murray asked that SDOT and WSDOT set up a “unified command” as soon as the settling was revealed late last week. The “unified command” included utilities “because it’s the underground stuff that’s most of concern right now,” Kubly said. “We’re in the data-gathering and data-analysis phase” right now, he added. “… This is a really serious incident, and I think the city’s response reflects that.”
3:33 PM: O’Brien asked if SDOT has the expertise to independently look at WSDOT data and make its own conclusions on whether the situation is safe or not. “Right now we’re looking over their shoulder and following their lead – it’s their structure,” Kubly replied.
Councilmember Tom Rasmussen notes that he and his colleagues are frustrated at not being able to understand yet “what are the facts, what is the data needed to determine if they agree or disagree with WSDOT” regarding safety. Looking over shoulder’s not good enough – “you need to be at their sides,” he tells Kubly, next asking if SDOT has the kind of expertise to do that. “Yes, we do,” he replies.
In response to questions from Councilmember Kshama Sawant, WSDOT’s Moore details his resumé and past projects he’s worked on (including the Tacoma Narrows Bridge) and his expertise in analyzing the stress on concrete and steel in structures like this. He notes that the City of Seattle designed the section of Alaskan Way Viaduct that is still up; the state designed the section that has been demolished and replaced in recent years. He again mentions some cracking in The Viaduct that is the result of original design that wasn’t to the kind of standard that would be expected today, but it is still capable of carrying the load it’s expected to. Project consultant Red Robinson details his background in evaluating settlement and water challenges in tunnel projects.
3:42 PM: Councilmember Bagshaw asks “what is your confidence level” in The Viaduct right now? Would you allow your child to walk or ride under it? WSDOT’s Moore says yes, absolutely. He says he has 95 percent confidence in it right now. “We do have certain locations which are suspect and settlements of a large magnitude give us some concern.” Bagshaw asks, “What about that 5 percent?” Moore says, “It’s that earthquake probability … we all know we have ground issues, as well as issues at the joints.”
Councilmember Jean Godden invites them back next Monday to provide not only an update but also what would happen if The Viaduct had to be closed. The daily inspections/surveying will continue in the meantime, WSDOT says.
When was the 1 1/4″ settlement noticed? asked Councilmember O’Brien. Reply: This weekend. So what about the earlier reports that the information had been out for a while? Actually, the anomaly was picked up by the contractor just before Thanksgiving, and surveying was done the weekend after Thanksgiving, but WSDOT had not confirmed it until last week, he was told.
O’Brien bristles at this and says they should be told before 100 percent confirmation – “if there’s an anomaly, I want to know. … I would rather you err on the side of letting us know what’s going on and saying ‘we haven’t confirmed it’.”
Now he asks – are they still dewatering or not? “They are still dewatering,” is the reply. As mentioned earlier, it’s not something that can be stopped abruptly. They’re expecting they WILL stop – but that’s pending data, so there’s a chance they might not have to.
What about building settlement/damage? An unspecified media report is mentioned. WSDOT says they haven’t seen anything from outside, but they’re planning another round of checks, and they’re going to offer a hotline to building owners that might have something to report.
O’Brien now presses the point – are you sure it’s safe to have vehicles on The Viaduct, if it was going to be closed when the tunneling was happening beneath it? The reply notes that there will be definite ground movement when the machine goes beneath it – not the same situation as exists now – and they would want to be able to act quickly if stabilization were needed. This is not the same kind of fast-moving situation, they explain.
Rasmussen asks how all this might affect the schedule. Too soon to say, he’s told. Even before this, WSDOT says, the contractor had told them verbally that the March restart is not likely. And they won’t know for certain where they’re at until the tunneling machine parts to be removed are above ground and taken apart and assessed.
O’Brien goes back again to the issue of how much settling is OK – is it specified in the contract? he asks. Yes, there are some specifics, he’s told. They’d like to be briefed on that, he subsequently says.
Bagshaw gets back to the access pit. Are the last 40 feet of digging ‘doable’? she asks. Yes, says WSDOT, depending on how all these new discoveries shake out. Do you know what you’re going to do about the dewatering problem? she presses. WSDOT says that since it’s a design-build contract, it’s up to Seattle Tunnel Partners to solve the problem.
Next up – WSDOT promises updates if there’s anything major before they return to the City Council next Monday at 9:30 am to talk about what Councilmember Godden, chairing this meeting, describes as “what if – what if we need to shut it down for a time,” etc. They’re moving on now at 4:01 pm to talk about the seawall project; we won’t be chronicling that. Once the meeting is over, we’ll watch for the archived video to be posted at SeattleChannel.com and will substitute it above when available.
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