The nearly two-mile-long, double-decked road tunnel replaces the seismically vulnerable Alaskan Way Viaduct (AWV) – a fixture of downtown Seattle’s Elliott Bay waterfront for 65 years that is soon to be demolished.

The tunnel opened to State Route 99 traffic on Feb. 4, following a weekend grand opening celebration, where the public had an opportunity to walk through the tunnel and learn more about the plans for Waterfront Seattle, a public park that will be developed along the site of the viaduct.

The Alaskan Way Viaduct Replacement Program is led by the Washington State Department of Transportation (WSDOT) in partnership with the Federal Highway Administration, King County, the City of Seattle and the Port of Seattle.

“WSDOT was faced with the need to replace a vulnerable and critical transportation corridor within Seattle’s downtown and waterfront core,” said Paula Hammond, WSP transportation market leader, who served as the Washington State transportation secretary from 2007-2013. “We had never developed a project of this magnitude of economic and quality of life importance and knew we had to bring our A-game through strong partnerships and community engagement to succeed.”

Since 2001, WSP has served as general engineering consultant (GEC) to the WSDOT for the $3.3 billion program and been involved in every aspect of the work from planning through construction. WSP provided the conceptual design and developed the technical requirements for the design-build tunnel project, prepared environmental documents and final design of some major project elements, and coordinated and managed a consultant team consisting of 62 subconsultants.

Check out a video of the AWV Replacement Program.

The significance of this project was highlighted by the attendance of an estimated 100,000 people at the Feb. 2-3 grand opening celebration, where visitors walked through the tunnel and learned about its path to construction, and bid farewell to the viaduct while welcoming the modern SR-99 tunnel to Seattle’s downtown landscape.

Grand opening activities included an 8-kilometer fun run, a 12-mile bike ride, an art festival and other activities on the viaduct.

Mike Rigsby was WSP’s project manager during some of the program’s most turbulent times, guiding its transition from a concept borne out of an urgent necessity to a practical solution that will have a major impact on downtown Seattle.

“The viaduct was an immense public safety risk, and we all knew we were racing against Mother Nature,” Rigsby said. “The technical complexity of planning, getting environmental clearance, and helping to contract for the largest bored tunnel in the history of the world was amazing. We were literally pushing the state of the art and involving every discipline.”

He said the program’s complexity “attracted the best people from around the company and around the country,” who rose to meet every challenge along the way.

“This program has been a huge part of my professional and personal life and has involved so many friends and colleagues over such a long time, that it is great to be able to celebrate the accomplishment of a huge goal and thank all involved,” Rigsby said. “I grew and learned so much about environmental, engineering, urban design, public involvement and so much more.”

“The success of the project is not just measured by the tunnel’s completion, but by the success and the careers of the team of people whose hard work completed it,” added Ginette Lalonde, current project manager for WSP. “Seeing Mike Rigsby’s steadfast leadership throughout the mid 2000’s, through general votes on AWV replacement alternatives and the rejection of one tunnel option, was inspiring. It’s truly amazing that the tunnel is completed and to watch how the program is transforming the City of Seattle.”

After years of planning and consideration of more than 75 possible options, the decision was made to bore a double-decked tunnel through downtown Seattle to replace the viaduct. Digging began in July 2013 as “Bertha”—the nickname given to the tunnel boring machine (TBM) in honor of Bertha Knight Landes, Seattle’s first female mayor from 1926-1928—began to make its way beneath downtown Seattle. Standing five-stories tall and weighing nearly 7,000 tons, Bertha was the world’s largest TBM at the time digging began.

Bertha’s enormous size provided the capacity needed to drill four traffic lanes at one time using a single bored tunnel – two lanes stacked upon two others – thus eliminating the need for a second bore. The upper deck carries southbound traffic, while the lower deck carries the northbound traffic.

Throughout the dig, construction monitoring was used to check how the ground and surrounding structures were affected by the tunnel construction. Typical vibration and noise monitoring was done for the portal constructions. Ultimately, more than 4,000 monitoring devices were used on the program.

“Buildings throughout the alignment were evaluated for impacts due to predicated settlement,” said Elizabeth Lundquist, WSP’s geotechnical engineer during tunnel construction. “Vibration monitoring along the overall alignment during tunneling confirmed that vibration from the TBM would have no negative effects.”

An additional 158 buildings along the alignment, including historic buildings, were monitored for movement throughout construction. Along with the building monitoring, extensive ground monitoring was performed to determine if settlement from tunneling was occurring.

In December 2013, tunnel progress hit an unexpected delay when the TBM stopped and had to be repaired before it could continue mining. Bertha started up again in February 2016 and on April 4, 2017, Bertha broke through into the disassembly pit and shortly thereafter built the tunnel’s final ring. Though the machine’s tunneling and ring-building work was complete, crews couldn’t complete roadway construction at the north portal until Bertha was removed. Once the ring-building work was complete, crews worked around the clock to disassemble the machine, making room for the roadway coming up through the tunnel behind it.

Hitachi Zosen, the machine’s manufacturer, dismantled Bertha’s signature 57-and-a-half-foot steel cutterhead and hauled most of it to a local steel recycler. Some remaining pieces of the cutterhead were donated to the Port of Seattle, while several cutting tools and the historic TBM’s control panel were donated to Seattle’s Museum of History and Industry.

Using highly sophisticated virtual design and construction (VDC) and building information modeling (BIM) techniques prior to construction, WSP created dynamic, three-dimensional animations to illustrate conditions at the site and help the client to visualize the impacts of proposed solutions.

“Design visualizations were an integral part of the program, used extensively to educate and inform the public, and as a primary design tool to effectively determine the viability of proposed concepts and eliminate conflicts between design elements for the replacement,” Lalonde said.

WSP created a video simulation to show, from a "worm's eye view," the proposed route for the tunnel and its proximity to other underground structures, including utilities and buildings. Another lifelike video prepared by WSP and released by WSDOT in 2009 showed a simulation of the viaduct’s collapse from a hypothetical seismic event similar to the Nisqually Earthquake, which struck the southern end of the Puget Sound region in February 2001. “That video attracted huge media attention and heightened public awareness about the life-safety risk of the seismically vulnerable structure,” Rigsby said.

WSP drew upon computer-aided design (CAD) and geospatial data to develop digital 3D and BIM for all major parts, pieces and processes of the project. These models enabled the project team to understand the project, design alternatives, and view traffic impacts and construction phasing from any point of view, allowing for more informed decision making by multiple stakeholders, while supporting public outreach efforts.

An example of the team’s extraordinary effort was with an early design-bid-build enabling project—the Holgate to King Street Viaduct Replacement. While the project was out for bid, a late change in the adjoining bored tunnel project required revising and resubmitting 75 percent of the design documents, which included changing and reprinting 1,400 documents over three months.

“One of the most challenging aspects was dealing with continually changing scopes of work and still meeting project milestones,” Lalonde said. “Even though final alignment decisions were delayed, the project had to remain on schedule.”

Since it first opened in 1953, the AWV has been one of the main north-south highway corridors through Seattle, and until its recent closure was carrying an average of 100,000 vehicles per day.

In addition to cutting off the city from its scenic waterfront, decades of daily wear and tear had exacted a heavy toll on the aging structure. The powerful Nisqually Earthquake caused extensive damage to the viaduct’s foundation, causing its closure for several months and highlighting the structure’s seismic vulnerability.

Shortly after the earthquake, WSDOT launched efforts to identify and implement the best solution to address this critical public safety and mobility liability, recognizing that it also provided the city with an opportunity to restore access between downtown and the waterfront and revitalize the waterfront area.

The tunnel was designed to meet stringent seismic standards to withstand a 2,500-year earthquake and features smart transit technology, including more than 300 cameras that monitor traffic, safety conditions and security.

“By its nature, moving transportation corridors underground frees up a lot of valuable surface land,” Mike Colyn, WSP’s project manager for Waterfront Seattle. “The AWV Program’s completion provides nine acres of new open space adjacent to the downtown Seattle waterfront and gives the waterfront back to the public.”

Waterfront Seattle is a $688 million program anticipated to reinvigorate the waterfront as an inviting, lively and family-friendly public space, connecting residents and visitors with cultural, commercial and civic destinations, and fostering growth and development opportunities for area businesses and nearby neighborhoods.

WSP is also part of the team helping to deliver this new amenity. As a subconsultant to the City of Seattle, WSP is leading the engineering component of the project and has provided 3D design visualization, cost risk assessment, project management, civil engineering, traffic engineering, stormwater management, storm drainage, electrical duct banks, risk management, and structural design support.

With the tunnel completed, attention can focus on the demolition of the viaduct and construction of a new Alaskan Way surface street along the waterfront that connects SR 99 to downtown. WSP is currently helping WSDOT respond to design-builder questions and coordinating responses with the City and State.

“The removal of the massive piece of infrastructure will substantially reduce traffic noise, and make the neighborhood more attractive and welcoming for residents and visitors alike,” Lalonde said. “We are looking forward to saying goodbye to the Alaskan Way Viaduct, and hello to the future waterfront.”

Completion of the Alaskan Way Viaduct Replacement Program is targeted for 2023.

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The Alaskan Way Viaduct Replacement Program was honored by the American Council of Engineering Companies (ACEC) with the national 2019 Engineering Excellence Grand Award for Transportation.

The project, which also received the ACEC-Washington Gold Award for Transportation, is one of three WSP projects that is currently under consideration for the ACEC’s Grand Conceptor award. The winner will be announced at the organization’s 2019 Engineering Excellence Awards gala event on May 7 in Washington, D.C.

Last year, the joint venture of WSP and HDR won the Grand Conceptor for the Bayonne Bridge: Raising the Roadway Project in Bayonne, New Jersey and Staten Island, New York. It was the fourth time that WSP won the ACEC Grand Conceptor award.