Milepost 31 Speakers Series – Bertha and Progress on the SR 99 Tunnel Project

You’ve been hearing a lot lately about WSDOT’s efforts to replace the State Route 99 Alaskan Way Viaduct (AWV). This is a big, complex undertaking. And as we all know, we’ve encountered some challenges. Join Matt Preedy, AWV Deputy Program Administrator, as he explains how WSDOT and STP are addressing these challenges and what the plan is to get Bertha, the SR 99 tunneling machine, moving again.

Thursday, March 6, 2014

6 to 6:30 p.m.

Milepost 31

211 First Ave. S. Seattle

Admission is free.

After the talk, be sure to leave enough time to explore the rest of the First Thursday Art Walk in Pioneer Square. Milepost 31 is open Tuesdays through Saturdays from 11 a.m. to 5 p.m., and stays open until 8 p.m. on First Thursdays. Free parking is available for First Thursday art walk patrons in Pioneer Square. Please visit www.FirstThursdaySeattle.com for more information about participating garages.

And don’t forget you can find regular updates about Bertha on Twitter by following @BerthaDigsSR99.

Alaskan Way Viaduct Replacement Project Update – February 2014

It’s been a busy start to 2014 with the opening of the South Atlantic Street overpass and crews working to get Bertha, the SR 99 tunneling machine, digging again. Here’s a recap of what we’ve been up to:

Milepost 31 Speaker Series: Learn about the South Atlantic Street overpass
On Monday, Jan. 27, we opened a new overpass to the west of Seattle’s stadiums, just south of Pioneer Square. The overpass allows traffic to bypass a busy railroad track that crosses South Atlantic Street. Before the overpass, train activity often blocked traffic for extended periods, which not only slowed truckers traveling to and from the Port of Seattle, but also created backups that stretched onto Seattle streets and Interstate 90. The overpass saves truckers as much as 20 minutes of travel time between the port and I-5 or I-90.

Visit Milepost 31 between 6 and 6:30 p.m. on Thursday, Feb. 6 to talk to staff about how the structure is changing traffic patterns in the area. Read more about the overpass here.

Further evaluation required before tunneling can resume
On Tuesday, Jan. 28, Seattle Tunnel Partners (STP) pushed the SR 99 tunneling machine – which had been stopped since Dec. 6 – forward approximately 2 feet. Moving the machine forward allowed crews to further test the functionality of the machine and determine if they could resume full-production mining. It also created sufficient space to build the next concrete tunnel liner ring on Wednesday, Jan. 29.

When the machine moved forward, crews saw indications of above-normal temperature readings in part of the machinery, similar to readings encountered before crews initially decided to stop mining on Dec. 6. On Wednesday, STP made adjustments and mined an additional 2 feet. The above-normal temperatures persisted, and STP made the decision to stop and perform further evaluations.

STP crews and tunnel engineers are operating the world’s largest tunneling machine in complex conditions. Although their investigations to date have provided a great deal of information, we will not be able to definitively identify the issue or issues facing the machine until tunneling experts complete their review. We will provide additional information as it becomes available.

Please visit our webpage for regular updates.

Alaskan Way Viaduct Replacement Project Construction Update – January 2014

Progress made in search for tunnel blockage

It was a busy holiday season for crews working to get Bertha, the SR 99 tunneling machine, digging again. While we still can’t say for sure what halted the machine on Dec. 6, we’re much closer to finding an answer than we were when all of this started.

Here’s a recap of what crews have been up to since the blockage occurred:

On Dec. 7, our contractor, Seattle Tunnel Partners (STP), began prepping the machine and surrounding environment so crews could inspect the cutterhead and excavation chamber safely.
On Dec. 17, a brief visual inspection of a small section of the excavation chamber and cutterhead found dirt, sand and cobbles – nothing unusual.
Over the holidays, STP crews were on-site to drill dewatering wells, maintain the machine and switch out cutting tools on the machine’s face.
Earlier this week, STP drilled 17 small-diameter, exploratory holes near the front of the machine to see if they could identify an obstruction. They encountered obstructions in four of the holes.
On Jan. 2, the water pressure was low enough and enough soil was removed from the excavation chamber to inspect the top 15 feet of the chamber.
This inspection showed an 8-inch-diameter steel pipe protruding through one of the many openings in the cutterhead. We believe the steel pipe is a well casing installed by WSDOT in 2002 after the 2001 Nisqually earthquake to better understand how groundwater flows through this area. The location of this pipe was included in reference materials in the contract.
We also believe at least some of the obstructions found by the exploratory holes are pieces of the 2002 steel pipe, which could be a contributing factor in the delay of boring.
Other potential factors include changing soil conditions that may have caused excessive wear of cutting tools, potential objects in front of the cutterhead or objects in the lower portion of the excavation chamber that still aren’t visible.

Next steps

STP is considering several options to remove the steel pipe and identify other potential obstructions.

While Bertha is stopped, other work is taking place. This includes:

Extensive construction on the north and south ends of the tunnel.
Preparatory work to dismantle the push frame and temporary tunnel rings in the launch pit.
Preparatory work to reconfigure the launch pitand build the roadway within the tunnel.

It’s too early to speculate about the cost or long-term schedule implications of this issue. We’ll continue to work with STP to determine ways to make up time lost during the blockage. Our focus is now on addressing this issue safely and in a timely manner so we can resume tunneling as soon as possible.