Time lapse camera image of the boring machine repair pit on Oct. 24. Credit: WSDOT
Perhaps the biggest problem with the Alaskan Way Viaduct Replacement Program is that the problems are not clear. Amid issues of contractual obligations, a faulty water main, building pressure on the excavation pit, strained communication between WSDOT and City Council, cracked streets and legislative restrictions on state money, one question prevails: How and when do we act to ensure public safety?
On Monday, after a briefing to the City Council from WSDOT, SDOT, SPU, Seattle City Light and DPD, some on the Council still felt unsure that anyone knew the answer.
WSDOT took measurements of the viaduct in October and found no movement. In late November, they measured again and, a week later, confirmed that portions of Pioneer Square and the viaduct may have sunk up to 1.5 inches. Because of the gap between readings — or as councilman Mike O’Brien called it, “the dark period” — no one is sure how the settlement took place. Was it all at once or gradual?
The question is important because WSDOT has not registered any new settlement in the last week. WSDOT officials point to this finding as a good sign that the viaduct and Pioneer Square have stabilized. However, they do so with some caution: Because they don’t know the pattern with which the settlement occurred, they cannot be sure that the viaduct has not, for example, settled in fits and starts.
Assuming the area has stabilized, then Bertha excavation may continue as normal. Clearly, for Bertha's sake — not to mention the more than $1 billion already buried in the project — this would be the preferred outcome.
If the area has not stabilized, however, then things are considerably more complicated.
First is the issue of what is causing the settlement. Blame has largely been placed on groundwater removal. Beneath our streets lie massive aquifers which exert enormous pressure on Bertha’s rescue shaft. To ensure the shaft’s stability, crews bleed off this water.
As the water is removed, the soil loses buoyancy and therefore the ability to hold as much weight, explained Red Robinson, director of an independent verification team to examine data on the viaduct’s sinking.
The areas where the groundwater is being removed, namely around South Washington street, seem to correlate with the sinking.
Images courtesy of WSDOT.
However, in what was surely an exercise in caution, WSDOT’s Viaduct Replacement Program Manager Todd Trepanier was not willing to confirm that groundwater is the problem. He did not offer an alternative. The viaduct has sunk before — 5 inches during the Nisqually quake — not as a result of groundwater.
Nevertheless, the briefing continued under the assumption that groundwater is the issue. It’s important to note that for WSDOT crews, the removal of groundwater from the pit around Bertha, is not optional at this point. Excavation of the pit can stop — Trepanier, in response to a question from counilmember Tom Rasmussen, confirmed he had indeed ordered the digging to stop. However, groundwater removal must continue to ensure the integrity of the Bertha rescue shaft.
In the case that the viaduct has not stabilized and WSDOT determines that groundwater pumping is definitely the cause, the pumps will need to be turned off and the excavation pit will need to be filled with water or dirt to counter the pressure on the shaft. The department would use water in the case of an emergency, quickly flooding the pit if the pumps need to be turned off immediately. The issue here is that water is difficult to remove and would jeopardize the structural integrity of the shaft. Dirt is the better, albeit slower, of two evils. But there’s something especially painful about the image of filling in the pit we’ve spent all this time digging.
At Monday's briefing, councilmembers — especially O'Brien, the most outspoken of the council members on the topic — searched for a timeline as to when WSDOT would decide to turn off the pumps. However, because no one is sure whether the settlement will continue, they were left unsatisfied. Councilmember Bruce Harrell was unsure as to who is in charge of monitoring and acting on data. He was assured that there is a team in place to do just that.
The ripple effects of a sinking city are enormous. Seattle Public Utilities director Ray Hoffman reported to the Council that “Pioneer Square water mains appeared to have settled beyond the replacement and repair threshold.” The mains, 70 percent of which were installed before 1930, will need to be replaced and/ or repaired. Though they can normally hold 90,000 gallons, they’ve been reduced to just 17,000 in light of the new findings. Their replacement is a potentially large and expensive project, although who would pick up the tab is unclear. More yellow SPU trucks than normal were seen staged around Pioneer Square Monday.
Additionally, WSDOT has found 4 buildings with “cosmetic damage”, i.e. cracks and fresh drywall dust on the ground. Two of those buildings featured cracks that were definitely recent; in the case of the others, it was unclear.
The biggest question is the use of the viaduct. How should the city react if it needs to be shut down? If there’s a silver lining to the viaduct’s inherent instability, it’s that contingency plans for its closure are already well established and, as anyone who’s ever been detoured knows, implemented regularly. Variable message signs are left permanently on location and all equipment lives on the back of a flatbed truck, Hoffman explained.
There are two closure scenarios for the viaduct, both of which would be in place for much longer than a day here or there. A closure is already planned for the period when crews are tunneling underneath the viaduct. If all goes according to plan, that will be for about two weeks. If the safety of the structure is compromised, the other scenario would be put into place. Who knows how long that would be for.
65,000 cars a day drive the viaduct. Contingency plan or no, re-directing that much traffic will be a pain. “Clearly if we’re going to move 65,000 cars off that viaduct, we need to invest in transit,” O'Brien said at a press briefing afterward. Yet, Trepanier explained at the council briefing that the $30 million in transit money the project was allocated has already been used up; an announcement that surprised at least O'Brien. And apparently legislation has forbidden the State of Washington from allocating more transit money to the project. Add it to the list.
O’Brien appeared far from satisfied. “It’s still not clear to me how a call will get made to shut down the viaduct.” He seemed particularly incensed when Trepanier said the project was 70 percent done, calling the number “misleading at best.” But today’s briefing showed that figuring out where 1.5 inches went — inches that could monumentally affect millions of people — and what to do about it, all while navigating contracts and politics, is no easy task.
If City Council President Tim Burgess has anything to do with it, the Bertha show will go on. "There’s no turning back at this point," he said. "The Governor agrees. The Mayor agrees. We must move forward.”
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