June 23 project update: Tunnel crews arrive at planned maintenance stop

Posted on Jun 23 2016 11:30 AM

It’s a reality faced by all car owners: Every few thousand miles, it’s time for an oil change. The same principle applies to tunneling machines, which experience normal wear and tear as they grind their way through the earth.

And so, after more than 1,500 feet of tunneling since their last pit stop, Seattle Tunnel Partners crews are set to begin regular maintenance on the massive machine. The front end of the cutterhead is now located approximately 120 feet beneath Spring Street, near Post Avenue. It will remain at that location for planned inspections and maintenance that are expected to last several weeks, though the duration of the stop will ultimately depend on the extent of the maintenance needs.

Performing regular maintenance is a critical part of ensuring the tunneling machine remains in good working order. All tunneling machines, no matter how large or small, need routine maintenance. STP will assess the condition of various systems throughout the machine over the next several days. This assessment will help them determine how much maintenance needs to be completed.

Crews are already preparing for their most challenging task: inspecting and replacing the tools that cut the ground in front of the machine. These tools wear down and may need replacement multiple times during the course of the tunnel drive. Inspecting and replacing the tools is challenging because it requires crews to work in hyperbaric conditions. For a detailed explanation of hyperbaric work, see Monday’s post.

Tracking progress

To date, crews have tunneled 3,088 feet, or nearly one-third of the total bored tunnel length. Almost half of their overall progress was accomplished in the past eight weeks. Crews have now installed a total of 466 concrete tunnel rings.

When all necessary machine maintenance is complete, crews will resume tunneling toward First Avenue. Our Follow Bertha page contains tunneling statistics and information about the conditions crews will face as they continue mining toward the north end of downtown. You can also follow progress on Twitter @BerthaDigsSR99.