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2:58 PM: That map (click the image to see the full-size version) is the main Alaskan Way Viaduct/Highway 99 Tunnel update so far today, six days after first word that some areas in the vicinity have “settled” more than an inch. You might have seen a version of the map on Publicola this morning; the version released by WSDOT this afternoon has added context and a slightly different color scheme. It shows settling of almost an inch and a half in some areas, but does not show the areas of “uneven” settling, says WSDOT, and the text of their update makes it clear this does not show what’s happened on The Viaduct itself:
Crews from WSDOT and Seattle Tunnel Partners are conducting ongoing surveys of the Alaskan Way Viaduct and ground to determine whether settlement is continuing near the SR 99 tunnel access pit. In general, the surveys include:
Twice daily manual measurements at the bottom of both the east and west columns of the viaduct.
Approximately every other day measurements of deep survey points. These are survey points more than 80 feet underground.Ground surveys of sidewalks and streets from Alaskan Way to Second Avenue and from Yesler Way to South King Street. Some areas are surveyed twice a day; other areas are surveyed once every two to three days.
Surveys of some buildings. Data is collected both manually and automatically and monitored daily.
The data from the ground surveys and deep survey points are represented on a survey point data map. This map does not represent data from building surveys or the surveys of the viaduct.
The map is a computer-generated approximation to show visually the survey results that were shared with the public on Dec. 5, which indicates approximately 1.4 inches of ground settlement near the access pit and a lesser amount of settlement in the surrounding area. It does not show differential settlement, which is uneven settlement that occurs underneath a particular building or structure.
Lastly, the map does not present conclusions about the effect of dewatering. Additionally, the colors have been modified to better show the change in settlement from high to low.
We asked WSDOT earlier today if the tunnel contractor was continuing with access-pit digging, estimated two days ago to have another day to go before they reached a point where they’d stop to evaluate. The reply said only that the December 9th update still applied. We’ve been watching the “live” construction camera, and the excavation equipment does seem to have been in action as the day goes on.
ADDED 4:15 PM: New development – a crack in King St. downtown, not far east of the “rescue pit.” A briefing by the mayor is expected soon.
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