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Retracing Bertha’s Journey


Photos from Seattle SR99 Tunnel ProjectSR99 Tunnel Project

January 11, 2018, marked the long-awaited closure of Seattle’s Alaskan Way Viaduct – the elevated section of SR 99 that is being replaced with a tunnel. Crews will need a few weeks to complete the transition to the new underground structure, so we decided it would be a great chance to reflect on the most talked about U.S. tunneling project in the last decade.

When the tunnel opens to traffic in February, it will mark nearly 10 years since then Washington Gov. Christine Gregoire finalized legislation that ended years of debate about the aging viaduct’s fate, and set the stage for a world-record breaking tunnel.

Editor’s note: All photographs in this special section are copyrighted and being published with permission of Catherine Bassetti.

Click on images to enlarge

SR99 Tunnel Project Background

The Alaskan Way Viaduct runs alongside the coast of Elliott Bay in downtown Seattle. Damage to the viaduct sustained during the 2001 Nisqually earthquake served as a wake-up call to Washington DOT (WSDOT) leaders – the aging viaduct, completed in 1959, needed to be repaired or replaced. Following a lengthy and sometimes contested planning period, Washington lawmakers voted to build a single, large-bore tunnel to house a double-deck roadway inside the tunnel for both northbound and southbound traffic.

SR99 Tunnel ProjectSR99 Tunnel Project





SR99 Tunnel ProjectSR99 Tunnel Project



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Getting Started

In December 2010, WSDOT selected Seattle Tunnel Partners, a joint venture of Dragados USA and Tutor Perini Corp., as the design-build contractor. The project comprised construction of more than 12,000 ft of roadway, including 9,270 ft of tunnel to be excavated by a 57.5-ft diameter EPB TBM – the largest in the world at the time.

SR99 Tunnel ProjectSR99 Tunnel Project

Going Underground

Construction got underway in 2011 with the TBM launch taking place on July 30, 2013, amid much fanfare. In December 2013, after excavating about 10 percent of the tunnel alignment, crews began to experience difficulties with TBM advancement, leading to an eventual shutdown and a repair plan that idled the machine for about two years.

SR99 Tunnel Project SR99 Tunnel Project





SR99 Tunnel Project SR99 Tunnel Project





SR99 Tunnel Project SR99 Tunnel Project





Saving Bertha

With the record-breaking machine (aka “Bertha”) stalled underground, the project team devised a plan to build a “rescue” pit to recover the machine and allow modifications and repairs. Mining would not resume in earnest until February 2016.

SR99 Tunnel Project SR99 Tunnel Project





SR 99 Tunnel Timeline

  • April 2013 – Bertha arrives in Seattle
  • July 30, 2013 – Mining begins
  • December 2013 – Mining stopped due to issues with tunnel advancement
  • May 2014-November 2015 – Tunnel construction halted as crews construct access shaft to remove
  • front end of TBM to perform repairs
  • December 2015 – Mining resumes
  • February 2016 – After a brief stoppage due to a sinkhole, mining resumes
  • Sept. 30, 2016 – Passes halfway point
  • April 4, 2017 – Bertha breaks through into the northern portal
  • April 21, 2017 – the last ring is installed, completing the tunnel drive
  • Jan. 11, 2019 – SR 99 Viaduct closed
  • February 2019 – SR 99 tunnel scheduled to open to traffic

SR99 Tunnel Project SR99 Tunnel Project





SR99 Tunnel Project SR99 Tunnel Project





Reaching the Finish Line

Upon resumption of tunneling, Bertha churned along as expected, breaking into the reception shaft near the Space Needle on April 4, 2017 – completing the largest TBM-built tunnel outside of Asia. The final piece of the 8,000-ton TBM was lifted out of the hole in August of that year, fully clearing the way for roadway construction.

SR99 Tunnel Project SR99 Tunnel Project





SR99 Tunnel Project SR99 Tunnel Project





Fact Sheet: The End of Bertha’s journey

Tunnel Breakthrough date: April 4, 2017
Distance tunneled: 9,270 feet
Tunnel rings built: 1,426
Soil extracted from beneath Seattle: 900,000 cubic yards
Lowest point relative to surface: 215 feet (near First Avenue and Virginia Street)
Machine Length: 367 feet
Weight: 7,982 tons
Number of propulsion jacks: 56
Total propulsion jack thrust: 44,000 tons
Number of cutterhead drive motors: 24
Total horsepower of motors: 16,500
Mining speed: 1 inch per minute (average)
Cutterhead Weight: 944 tons
Diameter: 57.5 feet
Cutting tools: 700 (approx.)
Rotation speed: 0 – 1.2 RPM
Total crew members operating and maintaining Bertha in a day: more than 100

A New Chapter

The opening of the SR 99 tunnel will allow the demolition of the viaduct and usher in a new era in the city’s rich history. The re-configured waterfront allows for a connected downtown and will serve as a model 21st century city.

SR99 Tunnel Project SR99 Tunnel Project





SR99 Tunnel Project SR99 Tunnel Project





Catherine Bassetti About the Photographer

Catherine Bassetti began her career in Madrid, Spain, as a commercial photographer and photojournalist.

As a native of Seattle with family roots in the city’s architectural heritage, Catherine was the on-site progress photographer/videographer for the SR 99 Seattle Tunnel Project for the past five years.

Bassetti Photography is a certified DBE firm based in Seattle, Washington, and available for contracting in the United States and abroad.

For more information or to purchase photos, contact Bassetti Photography at


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