(Added: Screengrab from ‘access pit’ camera – see newest image here)
7:59 PM: After today’s early-morning surveying of the Alaskan Way Viaduct, following Friday’s disclosure of a new inch-plus of “settling,” WSDOT has just published an update. While continuing to say that it’s safe to use The Viaduct, WSDOT says its contractor plans to stop the “dewatering” that was under way in the pit being dug to get to the tunneling machine:
WSDOT and Seattle Tunnel Partners conducted additional survey work early Sunday morning to further assess the amount and extent of settlement that recently occurred on and near the Alaskan Way Viaduct.
Some of the data was inconclusive and analysis is still underway; however, WSDOT observed that a small amount of differential settlement is occurring near the access pit. Differential settlement is when the ground settles unevenly over an area. When the ground settles evenly or uniformly over an area, there is less risk of damage.
The additional survey work did not find that the differential settlement has caused any new damage to the viaduct nor have we observed any damage to buildings or utilities in the surrounding area. On-the-ground surveys will continue this week by historic architects and structural engineers.
Public safety is our top priority and while we have not seen any damage, Seattle Tunnel Partners is taking the prudent step to stop dewatering. The contractor will work with its geostructural designer to stop the dewatering in a deliberate manner in order to ensure worker safety and the structural integrity of the access pit and surrounding structures.
Data analysis, collection and monitoring will continue and we will provide updates as we have new information to share.
“Dewatering” was being done as part of the access-pit excavation; as Mike Lindblom reported at SeattleTimes.com (WSB partner) after Friday’s report of settling, “Within the pit, water must be removed so that excavation machines sit on stable ground and aren’t scooping out an endless slurry.” The question now: Can digging continue without it? Yesterday marked exactly one year since the tunneling machine’s work stopped, after 1,000 feet of northward digging. WSDOT promises more information once it’s available, and we’re likely to hear more when the City Council’s prescheduled Alaskan Way Viaduct committee meets around 2:30 tomorrow afternoon.
ADDED 9:31 PM: We asked Viaduct project spokesperson Laura Newborn, who sent the above update, if this means no more digging, for now. She confirms to WSB that the contractor “will stop excavating.”
ADDED 11:11 AM MONDAY: This morning, spokesperson Newborn says that means excavation stops if/when dewatering stops, but she doesn’t have information right now on whether that’s happened yet.