After mining through more than 9,000 feet of Seattle underground, and rebounding from a lengthy breakdown and repair, Bertha the tunneling machine is poised to bust through its final obstacle on Tuesday. It’s a historic moment for a project aimed at replacing the aging Alaskan Way Viaduct, a fixture of the city’s waterfront transportation needs.
Representatives from Seattle Tunnel Partners and the Washington State Department of Transportation said Monday that the giant machine is just 25 feet from the end point and daylight near the tunnel’s north portal at the intersection of Sixth Avenue North and Thomas Street.
Once it mines through a 5-foot-thick concrete wall, Bertha will emerge into a nearly seven-story-deep disassembly pit where it will eventually be cut up, hoisted to street level and trucked away.
“What a beautiful day today,” said Joe Hedges, a project administrator with the Alaskan Way Viaduct Replacement Program, as he and STP project manager Chris Dixon briefed news media Monday on the status of Bertha’s breakthrough. “I want to compliment STP, their tunnel crews and WSDOT for this historical day. Washington state and Seattle should have a lot of pride today.”
With the sun shining and the Space Needle piercing the blue sky overhead, Hedges said he was very excited about the fact that a five-story tunnel had been mined through the heart of the city. But, he said, “we’re not at the fourth quarter … we’re only at halftime” and a lot of work still remained to be done before a new 2-mile, double-decker stretch of Highway 99 would open to vehicles in January 2019.
Early Tuesday, the front end of the massive tunneling machine is expected to be visible as it reaches the disassembly pit. WSDOT said that machine operators will proceed very slowly and it could take hours to bust through. After that, it will be weeks before the machine is in its final position in the disassembly pit.
STP has activated a time-lapse camera so the public can witness Bertha’s emergence and then the ongoing disassembly of the machine.
Dixon said Monday that concrete will begin to fall off the face of the wall as Bertha emerges and a large amount of water will be sprayed into the pit to minimize the dust. After cleanup, interior bracing in the pit will be removed. The cutterhead and machine will eventually be cut into 20-ton pieces which can be loaded onto trucks.
“There’s so many things that are just massive on this job and so many bells and whistles on this TBM (tunnel boring machine) that you don’t normally find on TBMs,” Dixon said in summing up the unique aspect of the SR 99 project. “There’s a lot of things that need to be considered when you scale up something that’s normally a very typical, run-of-the-mill operation into something as large as this.”
The long road
The arrival of Bertha at the end point and its imminent breakthrough comes almost four years and many millions of dollars after the machine first began boring operations.
Bertha’s 9,270-foot journey began on July 30, 2013, at the southern end of downtown Seattle, at Railroad Way South and South Washington Street. Five months later, in December 2013, approximately 1,000 feet into the operation, tunneling was stopped when Bertha’s cutterhead was damaged. What caused the damage is the subject of ongoing litigation between WSDOT and the contractor.
An access pit was dug to remove the front of the machine and rebuild it and tunneling didn’t resume until December 2015.
The machine churned through waterfront soils, crossed beneath the viaduct foundation, and made its way under the Belltown neighborhood throughout 2016, stopping for routine maintenance along the way. Systems to monitor surrounding buildings and roadways kept a close eye out for movement of the ground beneath. Workers running and maintaining the machine deep beneath Seattle were exposed to hyperbaric conditions in one of the most extreme work environments imaginable.
Trailing behind the machine as it cut the path for the tunnel and placed the giant concrete rings to make up the tunnel’s outer wall, is a major road-building operation. The new Highway 99 will be a double-decker route and construction of the upper deck has been happening during tunneling, with about a mile complete.
The cost of the entire project to replace the viaduct — tunneling, highway building, viaduct teardown, etc. — is $3.1 billion and consists of 32 different projects. WSDOT asked the legislature for $60 million for the next budget (2017-19) to pay for added program costs from the tunnel project delays. Last year, WSDOT told the legislature that costs could go as high as $149 million due to risks in tunneling, but now that tunneling is complete, that estimate may decrease, according to WSDOT.
The entire tunnel is to consist of 1,426 concrete rings, and as of Monday, ring No. 1414 had been placed.
Dixon said he was always very confident that STP would get the machine repaired and tunneling would resume, even as calls to scrap the expensive project grew louder.
“It’s really a testament to all the people on the project, the people on the TBM, the people managing the operation,” Dixon said. “All of the support staff that we have, just everybody involved with Seattle Tunnel Partners has really focused on everything that needs to be done, we’ve gotten into a very good rhythm. My hat’s really off to everybody on the team for getting us where we are today.”
On Monday, as workers prepared for Tuesday’s big day by hanging banners on the pit walls, Hedges said they were in a great place, just feet from the finish line.
“We have a lot more work yet to be done, but what this really does, is you look at this and you say, ‘This is success,'” Hedges said. “The highest risk was getting the bored tunnel. So I’m excited just to be here. It’s a good day.”
Check back with GeekWire on Tuesday for more on Bertha’s breakthough. And look back on more of GeekWire’s extensive coverage of Bertha and the project to replace the Alaskan Way Viaduct in Seattle.
