Bertha Burrows Under Seattle

Bertha's cutterhead — Bertha’s cutterhead eases down into the launch pit just before the tunneling machine’s July 2013 launch. *Source: Washington State Department of Transportation*

Bertha begins — Bertha chews through her first bits of earth on July 30, 2013. She’ll dig two miles of tunnel for the State Route 99 project. *Source: Washington State Department of Transportation*

Micropile installation — Drillers install micropiles in April 2012 next to the Alaskan Way Viaduct to protect it from Bertha’s activity many feet below the surface. *Source: Washington State Department of Transportation*

Soil sampling — Like any major infrastructure project, a lot of preparation work went into the Alaskan Way Viaduct Replacement project. Here, drillers take samples to better understand the soils along the tunnel route. *Source: Washington State Department of Transportation*

Supporting structures — Crews install steel supports in October 2012 to limit settlement under Seattle’s Polson Building. Bertha’s route would pass nearby. *Source: Washington State Department of Transportation*

Pile wall — Construction crews build the pile wall box that would become Bertha’s “safe haven,” where engineers could work out kinks before getting tunneling under way. *Source: Washington State Department of Transportation*

National Driller freelancer Holly Case recently told readers about an ambitious tunneling project at the Port of Miami. Today, I want to talk about another large-bore tunneling project, this one across the U.S. in Seattle.

The Alaskan Way Viaduct Replacement project began in earnest in late July, when the tunneling machine Bertha broke ground. Berta will bore 2 miles of tunnel under downtown Seattle, making way for a replacement spur of State Road 99. The tunnel's expected opening in late 2015 will allow the demolition of the current Alaskan Way Viaduct strip of SR 99, clearing the way for development of a new, waterfront public space downtown.

A Bit About Bertha

Bertha's cutting face measures 57.5 feet, which the project's website calls the "world's largest." She certainly tops Harriet, the tunnel-boring machine used in the Miami project. Harriet measures 43 feet top to bottom. (Why do tunneling machines always get feminine names? That's the subject of another post.)

The Washington State Department of Transportation held a competition to name the $80 million tunneler. The winning name, Bertha, was submitted by an elementary school student.

Hitachi Zosen Corp. built Bertha in Osaka, Japan. After manufacture and testing, Hitachi Zosen dissembled Bertha into pieces under 900 tons for shipment. The company shipped her across the Pacific Ocean and she arrived in Washington's Elliot Bay on April 2. Hitachi has a solid track record, having built more than 1,300 tunneling machines. Bertha, the company's website says, features an advanced slurry pressure system "designed to work with the variety of different soil types found in Seattle."

Workers in Seattle reassembled Bertha in the projects 80-foot deep launch pit, and tunneling started July 30.

About the Alaskan Way Viaduct Project

A group called Seattle Tunnel Partners secured the contract for the $1.09 billion project. STP is a joint venture of Dragados USA and Tutor Perini Corp. On its website, Dragados, founded in 1941, touts its experience boring more than "140 miles of road tunnels." It also has extensive experience in metro and rail tunneling, sewer and water tunneling, and mine access. Tutor Perini offers a range of civil and building construction services, and has worked on a range of highway, subway and other projects.

The project's website has lots of other information, including details about Bertha and a map of her route.

A History Lesson

The Seattle project has shaky roots. An earthquake in 2001 damaged the existing SR 99. The 6.8 magnitude temblor damaged elevated sections of the highway running through Seattle's downtown area. Engineers stabilized the road's supports, but city officials quickly realized the necessity of a replacement.

Any large infrastructure project involves a lot of wrangling--legal, political and otherwise. In Seattle's case, it took more than 10 years. The massive project finally got bid out and under way. Now, on her productive days, Bertha chews through 35 feet of soil per day. Join me in following her progress on Twitter at twitter.com/BerthaDigsSR99. In fact, Bertha announced Monday on Twitter that she's started moving after a pause in the project.

Jeremy Verdusco worked as Editorial Director for The Driller from late 2012 through early 2024. He’s worked in publishing since 1997, including stints as a reporter, copy editor, page designer and technical writer.

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