Bertha reaches planned maintenance stop — next move is under Alaskan Way Viaduct

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The Bertha tunnel-boring machine.

SEATTLE — Bertha, the State Route 99 tunneling machine, reached a planned maintenance stop near Yesler Way on Saturday after successfully mining almost 300 feet during the past three weeks, the Washington State Department of Transportation said Monday.

According to the contractor, Seattle Tunnel Partners, the machine functioned within required operating parameters. STP has now mined a total of 1,560 feet.

STP will spend up to one month inspecting the machine and performing planned maintenance. Scheduled work includes:
  • Performing hyperbaric interventions
  • Inspecting the cutterhead, main drive unit and screw conveyor
  • Replacing cutting tools
  • Extending the conveyor belt and the high-voltage cable
 When STP has completed its maintenance work, crews will tunnel out of the maintenance stop and beneath the Alaskan Way Viaduct. WSDOT plans to close the viaduct for approximately two weeks to allow the machine to pass beneath the structure.
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