ROAD TUNNEL: WSDOT has plan for repairing Alaskan Way TBM

Drivers on S.R. 99 in Seattle will soon see a noise-blocking wall rise out of the ground near the spot where crews will dig a pit to reach and repair Bertha, the S.R. 99 tunneling machine. The double-plywood wall, which will be as tall as the lower deck of the Alaskan Way Viaduct, is designed to shield neighbors from construction noise associated with the repairs. It will stretch along the west side of the viaduct between South Jackson and South Main streets. Construction of the wall should take about two weeks.

The contractor for the tunnel project, Seattle Tunnel Partners (STP), is still finalizing their repair plan for the machine. Crews will dig a 120-ft-deep pit in front of the machine, which is located about 60 ft below the surface between Jackson and Main. The machine will then tunnel forward into the pit so crews can partially disassemble it and make repairs to the seal system and main bearing. These conceptual drawings illustrate the basic idea.

Because this is a design-build contract, STP is responsible for developing and implementing the plan to fix the machine and resume tunneling. Schedule and budget impacts of the tunneling stoppage, which began in December 2013, will not be known until after the plan has been finalized. The contract currently requires STP to open the tunnel to drivers by Jan. 2, 2016.