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Bertha’s work under Seattle’s viaduct has ‘no adverse influence’ on the aging structure

Crews monitored the Alaskan Way Viaduct as Bertha tunneled underneath the aging structure. The state reports tunneling did not have any adverse impacts on the viaduct and reopened it days ahead of time. (WSDOT)

Bertha performed as advertised when the tunnel boring machine plunged under the Alaskan Way Viaduct, allowing the state to reopen the roadway four days ahead of schedule.

Engineers determined that tunneling under the viaduct did not cause any issues with the aging structure. Todd Trepanier with the Washington State Department of Transportation (WSDOT) says that is because the tunneling contractor was able to maintain control of the ground as crews continued excavation.

“This early opening is possible due to [Seattle Tunnel Partners’] ability to control the ground during this tunneling in this area, having no adverse influence on the viaduct structure,” he said.

Related: Seattle tunnel progress a major contrast to past problems

After about 318 feet, the state decided it was safe to reopen the viaduct.

Trepanier says Bertha began to perform as expected once it hit more solid soil.

But Travis Phelps with WSDOT admits there was some concern.

“With Bertha coming out of the repair shop and then straight to tunneling under the viaduct, I think a lot of us had some nervous tension,” he said. However, Phelps says the department is pleased the contractor reached this point.

A lot of people on social media are questioning whether this was a case of over-promising so Seattle Tunnel Partners and WSDOT could have a much-needed PR win on the project. There were also questions of whether Seattle Tunnel Partners would get some sort of bonus out of this – which it does not, according to Trepanier.

Bertha still has about 7,800 feet to go before the machine’s journey ends at the north portal.

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