March 14 project update: Bertha reaches planned maintenance stop

Posted on Mar 14 2016 3:29 PM

On Saturday, Bertha, the SR 99 tunneling machine, reached a planned maintenance stop near Yesler Way after successfully mining almost 300 feet during the past three weeks. According to Seattle Tunnel Partners, the machine functioned within required operating parameters. STP has now mined a total of 1,560 feet. 

STP will spend up to one month inspecting the machine and performing planned maintenance. Scheduled work includes:
  • Performing hyperbaric interventions
  • Inspecting the cutterhead, main drive unit and screw conveyor
  • Replacing cutting tools
  • Extending the conveyor belt and the high-voltage cable 
When STP has completed its maintenance work, crews will tunnel out of the maintenance stop and beneath the Alaskan Way Viaduct. WSDOT plans to close the viaduct for approximately two weeks to allow the machine to pass beneath the structure. 
We will provide the public with advance notice of the closure, but the start date isn’t yet known. It will depend on the amount of work that must be completed while the machine is in the maintenance stop. STP won’t know the extent of the needed maintenance until inspections are complete, a process that could take approximately two weeks of the one-month maintenance period. Check for additional details as the closure approaches.
A closer look at Bertha’s planned maintenance stop
The maintenance stop – sometimes referred to as Safe Haven 3 – is essentially a solid concrete block built underground near Yesler Way. Being in concrete, rather than unprotected ground, allows STP to perform maintenance more easily. This is because the concrete provides a stable environment around the machine as crews work in hyperbaric conditions within the excavation chamber behind the cutterhead. 
Maintenance stop rendering
Bertha's planned maintenance stop is located more than 60 feet underground, approximately 450 feet north of the access pit and 40 feet west of the viaduct. 
Construction of Bertha's planned maintenance stop in 2013
Crews inject grout into the ground in 2013 during construction of Bertha’s planned maintenance stop.
Recent updates 
March 7 project update: Demonstration period complete, mining continues
March 3 project update: Bertha tunneling toward South Washington Street
Feb. 26 project update: Mining continues
Feb. 23 project update: Seattle Tunnel Partners resumes mining
Feb. 5 project update: Seattle Tunnel Partners set to replace damaged pier
For earlier program updates, please visit our archive page.