The part of the SR 99 tunnel built without Bertha

Posted on Dec 7 2015 9:20 AM
Bertha is one part of the construction story of the State Route 99 tunnel. The other part of the story is the approximately 20 percent of the tunnel designed to be built without a tunneling machine. Seattle Tunnel Partners bored more than 1,000 feet of tunnel before they stopped to repair Bertha. While the repairs were ongoing, an additional 1,200 feet of cut-and-cover tunnel was built by the contractor. It’s still all the SR 99 tunnel  just different methods of construction.
Using cut-and-cover construction at both ends of the bored tunnel gives Seattle Tunnel Partners the best way to gradually connect the northbound and southbound lanes of SR 99  which run side-by-side on the surface – to Bertha’s piece of the tunnel, where the roadway becomes a double-decker.
Most of the cut-and-cover construction has taken place underground, out of sight of the public. This video gives a close-up look inside the newest part of the project to learn more about the part of the SR 99 tunnel built without Bertha.
Approximate tunnel length:
  • Bored and cut-and-cover tunnel combined: 11,000 feet 
  • Bored tunnel: 9,300 feet (1,000 feet bored to date)
  • Cut-and-cover tunnel: 1,700 feet (1,200 feet built to date)
The video below illustrates how a cut-and-cover tunnel is built.
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