Early yesterday morning, December 22, Seattle Tunnel Partners (STP) moved the State Route 99 (Alaskan Way Viaduct Replacement) tunneling machine ‘Bertha’ forward and built a tunnel ring at the bottom of the 120-foot-deep pit crews built to access and repair the machine. STP plans to tunnel a short distance further in the access pit before giving crews a break for the holidays.
After the holidays, STP plans to mine out of the access pit toward a planned maintenance stop 450 feet to the north. Along the way crews will mine slowly while installing tunnel rings and continuing to run tests. When the machine reaches the maintenance stop – essentially an underground block of concrete just south of Colman Dock – crews will perform maintenance and make final adjustments before driving beneath the seismically damaged viaduct.
Tunneling under the viaduct will require a full closure of SR 99 through downtown for approximately two weeks. The contractor’s latest projections show that the closure will occur in March, but the actual closure date will depend on Bertha’s progress.
STP and Bertha’s manufacturer, Hitachi Zosen, are responsible for the repair effort, including the schedule. While the machine was under repair, STP continued essential work at the future tunnel portals, including construction of ramp and highway connections, and the buildings that will house tunnel operations.
STP crews halted tunneling in December 2013 after the machine overheated. After an investigation, STP discovered damage to the main bearing seal system and determined it needed to be replaced along with the main bearing. The cause of the damage has not been determined. Responsibility for costs associated with the delay will be determined through the process outlined in the tunnel contract.
- Dec. 6, 2013: Seattle Tunnel Partners stops tunneling due to high temperatures in the 57.5ft (17.5m) diameter Earth Pressure Balance TBM. At that point, 1,023 feet of SR 99 tunnel was built.
- STP initially believed there was an obstruction in front of the machine, but no obstruction was found.
- STP cleaned the cutterhead spokes and replaced cutting tools on the cutterhead. Overheating persisted when STP attempted to move the machine forward.
- Further investigation revealed damage to the seal system that protects the main bearing. STP and machine manufacturer Hitachi Zosen chose to repair the tunneling machine from above ground.
- Additional damage to the machine was discovered after the front end of the machine was disassembled on the surface.
- The cause of the damage to the tunneling machine has not been determined.
- To access the machine, STP built an 80-foot wide, 120-foot-deep access pit in a work zone west of the Alaskan Way Viaduct.
- STP moved the machine into the access pit and on March 30, 2015, lifted the 2,000-ton front end to the surface.
- Between March and August 2015, Hitachi Zosen conducted repairs, including a re-designed seal system.
- On Aug. 24, 2015, STP lowered the front end of the machine back into the ground to continue repairs. This video, narrated by STP’s project manager Chris Dixon, explains some of the repairs and the steps needed to get Bertha tunneling again.
- In December 2015, Seattle Tunnel Partners completed reassembling the machine, refilled the access pit and continued testing the machine within the backfilled access pit.
Below is a new time-lapse video showing STP’s work to backfill the access pit. Crews finished backfilling the pit over the weekend.