(Added: Recent WSDOT photo of access pit, shared via Flickr)
5:13 PM: WSDOT says it will be inspecting the Alaskan Way Viaduct and vicinity this weekend after detecting more ground settlement. Seattle Times (WSB partner) transportation reporter Mike Lindblom reported it earlier this afternoon, and now WSDOT has this statement on its website:
Public safety is our top priority, which is why we installed a state-of-the-art settlement monitoring system as part of the SR 99 Tunnel Project. Recently, that system detected approximately one inch of ground settlement near the pit Seattle Tunnel Partners is building to access and repair the tunneling machine. We have also seen the same amount of settlement on the Alaskan Way Viaduct; the amount of settlement lessens in the surrounding area.
Some settlement was expected during tunnel construction and while the tunneling machine repair work was underway. This settlement appears to have occurred in the last month.
We have observed no new damage to the viaduct nor have we observed any effect on buildings or utilities in the surrounding area. WSDOT crews are conducting additional surveys this weekend to verify this information, including an inspection of the viaduct and a visual inspection of the adjacent areas.
While we are conducting this additional work, we are confident that there is no risk to public safety. We will provide an update early next week.
Even before the tunneling project began, Viaduct managers had noted ongoing settlement, usually described as minor (as in this 2010 report). Nothing about settlement was mentioned at the regional stakeholders’ meeting we covered last Monday, but we imagine it’ll come up when the City Council’s Viaduct Committee meets early next week.
6:08 PM: We asked WSDOT spokesperson Laura Newborn if this is the reason the Saturday night/early Sunday Viaduct closure was expanded to both directions, and she confirmed that was done “so extra survey work could be completed.”