Seattle tunnel machine Bertha reaches halfway point — here’s a rare look inside the massive project

The SR 99 tunneling machine has passed the halfway point on its long journey beneath Seattle, and officials stood 10 stories below street level on Monday to show off where Bertha is expected to punch through next spring.

“This is the best hole in town,” said Joe Hedges, administrator with the Alaskan Way Viaduct Replacement Program as he set off with GeekWire and other media outlets into the receiving pit at the north end of the project, at Sixth Avenue North and Thomas Street.

On Friday, the machine tunneled past Pike Place Market to go beyond the halfway mark of the 9,270 feet it must travel to complete the new tunnel. Bertha has mined 4,662 feet and installed 709 of the 1,426 rings which will make up the tunnel’s outer wall.

Tunnel pit
A view from street level down into the receiving pit, 100 feet below.
The machine is currently about 190 feet below First Avenue between Pike and Pine Streets and is just a few days away from stopping for routine maintenance and hyperbaric interventions which will last a month or so.

One hundred feet down in the completed shaft where Bertha will pop through and eventually be disassembled, Hedges called it “a significant day.”

“We are closer to this point than we are to the starting point, over 50 percent now,” he said. “Today is a great day. We celebrate the accomplishments of 1,000 people, over two decades of work, that are really going to contribute to the transformation of Seattle’s waterfront for the next two centuries.”

Hedges said as the machine has been moving up First Avenue there has been almost zero ground movement, and Seattle Tunnel Partners has been doing a “wonderful job with regards to protecting, preserving and maintaining Bertha.”

Tunnel pit
Chris Dixon, left, project manager with Seattle Tunnel Partners, and Joe Hedges, administrator with WSDOT’s Viaduct Replacement Program.
Tunnel pit
Rebar from the double-deck roadway hangs overhead as members of the media hear from SR 99 tunnel project officials Monday.
Chris Dixon, project manager for Seattle Tunnel Partners, said Bertha has traveled 3,000 feet since April.

“Just on a straight line interpolation, we’re looking at 7 1/2 more months of tunneling, if the next 7 1/2 months go as the last 5 months,” Dixon said. “It puts the hole-through date here sometime in May of next year.”

Hedges said it’s nice to be optimistic, but everyone remains aware of what still lies ahead.

“Fifty percent is a major milestone for our program, but I do not want to distract that there’s 50 percent to go,” Hedges said. “In that 50 percent there’s a lot of unknowns, a lot of uncertainties. And what we need to do is basically be consistent with our approach. Let’s get there and let’s get there safely.”

“Fifty percent is a major milestone for our program, but I do not want to distract that there’s 50 percent to go. Let’s get there and let’s get there safely.”
The tunnel boring machine is said to be performing well and handling the ground conditions, including rocks in the range of 2 feet in diameter.

It wasn’t always smooth sailing for the multi-million-dollar Bertha, which started its operations on July 30, 2013. Six months into tunneling it stopped due to overheating and eventually the cutterhead and cutter drive unit had to be lifted out of an 80-foot diameter pit on March 30, 2015.

The machine was repaired, put back in the ground and resumed mining on Dec. 22, 2015.

Dixon said operations systems on Bertha ensure that the machine should be “dead center” when she reaches the extraction pit. Struts and whalers in place now to hold the breakthrough wall in place will be removed when Bertha has reached the other side of it.

The machine will proceed to the center of the pit before it is disassembled and lifted out.

Tunnel pit
A view toward the north end of the pit shows the northbound (lower) and southbound lanes of SR 99.
The light at the end of the tunnel.
Tunnel work
A lone worker smooths the surface in a ventilation area adjacent to the main tunnel.
At the north end of the pit, the double-deck roadway that carries northbound and southbound lanes into and out of the tunnel is visible, awaiting future connection to what is being built in Bertha’s wake.

Outside of the tunnel, ramps and roadways into, out of and around the tunnel are already in place. Work continues on the tunnel operations building which will eventually cover the area that is the receiving pit now.

It’s quite the high-tech corridor, as the Bill and Melinda Gates Foundation sits on one side of the north portal, and cranes and new buildings in and around Amazon’s South Lake Union campus are visible just to the east.

According to WSDOT, once tunneling is complete, STP will continue work on the tunnel’s interior structures and systems. Future contractors will make necessary highway connections. With that work scheduled to last into late 2018, WSDOT estimates the SR 99 tunnel would open to traffic in early 2019.

Tunnel work
A panoramic view captu

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