Digging resumes on Bertha

Key Developments:

  • Tunneling has resumed on State Route 99 as Washington State Department of Transportation lifted the governor's suspension on Bertha operations in January after two "safety incidents."
  • Gov. Jay Inslee's suspension came after a sinkhole formed on the State Route 99 tunnel project in ground that the drill Bertha mined.
  • The sinkhole formed as Seattle Tunnel Partners – the contractor – was dealing with a problem with hauling away excavated soil on barges.
  • Bertha is digging a tunnel to eventually replace the Alaskan Way Viaduct. The project has been delayed several times over the last few years.

The troubled tunnel machine Bertha started digging the State Route 99 tunnel again Tuesday morning, six weeks after Gov. Jay Inslee brought drilling to a halt because of a sinkhole

The machine advanced about three feet by mid-afternoon, after the Washington State Department of Transportation gave provisional approval to the contractor, Seattle Tunnel Partners, to advance another 160 feet as part of a review period.

WSDOT officials say STP adopted new protocols for weighing and calculating soil as it comes off the conveyor belt, a way to prevent future sinkholes.

Contractors also brought in four tunneling experts for the new demonstration phase.

"I think of them as changing the quarterback out or at least the tight end and I think that's important for having confidence," Inslee told reporters.

If all goes well with the first 160 feet, Bertha will continue a hundred feet more to a planned maintenance stop, where it will spend several weeks before tunneling beneath the viaduct.

The state is not allowing contractors to remove excavated dirt by barge after a January incident when soil spilled into Elliott Bay and a pier was damaged.

The dirt is now going to a muck pit, and then into dump trucks, while the state waits on a report from contractors about proper barge loading.

Seattle Tunnel Partners is permitted to tunnel forward and install approximately 25 concrete tunnel rings.

During this time, they must demonstrate that they have implemented a number of changes to ensure they can safely continue mining.

These changes include:

  1. Updated tunnel work and quality plans, including calculations of the amount of soil removed during excavation of each tunnel ring.
  2. Realignment of key personnel within their quality assurance program.
  3. New quality assurance protocols.
  4. New personnel at key positions within the tunneling operation.
  5. Restructured daily tunneling meetings that include additional participants and protocols.  

WSDOT will fully close SR 99 through downtown for approximately two weeks while the machine passes beneath the viaduct. The closure date will depend on the tunneling machine's progress. Check www.99closure.org as the closure approaches for additional details.