March 23 project update: Machine inspections underway

Posted on Mar 23 2016 4:56 PM
Inspections and routine maintenance of the SR 99 tunneling machine are ongoing as Seattle Tunnel Partners continues preparing the machine for its drive beneath the Alaskan Way Viaduct.
Crews have been performing planned maintenance since the machine reached a maintenance stop earlier this month. They’ve also been preparing for a series of inspections that must occur in hyperbaric conditions. Hyperbaric conditions are those in which the air pressure is greater than the atmosphere we live and breathe in every day – similar to what scuba divers experience during the course of an underwater dive. This post explains the process for completing hyperbaric work.
So far this week, STP crews have completed a total of 10 hyperbaric shifts in the chamber behind the tunneling machine’s cutterhead. Most of that time has been devoted to cleaning muck from the cutterhead openings and building the platforms crews will stand on as they perform the inspections. 
The inspections are expected to take several more days. STP will determine the expected duration of the remaining maintenance based on the results of the inspections.
The end of the maintenance period will usher in the next step in Bertha’s journey: a trip beneath the 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. Check for additional details as the closure approaches.
Recent updates 
March 14 project update: Bertha reaches planned maintenance stop
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
For earlier program updates, please visit our archive page.