SR 99 tunnel crews lowering groundwater to inspect TBM obstruction

SEATTLE — Seattle Tunnel Partners (STP), Washington State Department of Transportation’s (WSDOT’s) design-build contractor for the SR 99 tunnel project, has taken their first step toward identifying and removing the potential obstruction that stopped the progress of the tunnel boring machine (TBM) last week. STP is installing up to eight wells approximately 120 feet deep on the construction site near the machine, which is located about 60 feet below the surface between South Jackson and South Main streets, to the west of the Alaskan Way Viaduct. The wells will lower the water pressure in the ground, to create a safe environment for workers to enter the excavation chamber at the front of the machine and to begin to assess the situation. High groundwater pressure combined with loose soils has to this point prevented safe worker access.

“We’re confident STP has the right people and the right approach in place to safely determine what’s causing the obstruction,” said Matt Preedy, Alaskan Way Viaduct Replacement Program deputy administrator. “Once they know what the obstruction is, our contractor will be able to select the best path forward.”

Well installation started on Thursday and will continue into next week. STP hopes to begin inspecting the machine by late next week.

To date, crews have successfully installed more than 1,000 feet of tunnel. Work continues inside the tunnel structure as well as in the north and south portal areas.

For more information about the SR 99 Tunnel Project, part of the Alaskan Way Viaduct Replacement Program, visit www.alaskanwayviaduct.org.