The cutter head for Bertha, the tunneling machine must be inspected, cleaned and parts replaced in place, some 160 feet under the city of Seattle. That means workers must work short shifts, undergo pressurization and depressurization procedures, just like divers working underwater, plus multiple health exams.
The workers on Bertha, the tunnel drilling machine making its way under downtown Seattle to replace the Alaksan Way Viaduct, are according to WSDOT almost literally underwater.
Since the depths reached by Bertha are deep into the water table at 160 feet down, workers must treat shifts up at the cutting head like underwater dives, completely with pressurization and depressurization procedures and multiple physical exams. The work done by Ballard Marine Construction and SeattleTunnel Partners requires that the cutter head be maintained directly by cleaning, inspection and when required, replacement of worn parts.
Since the maintenance period began on Jan. 5, crews have replaced 250 cutterhead tools (see example below) over the course of 184 hours of hyperbaric shifts. This maintenance is critical as STP prepares for the final 25% of the tunnel drive.
STP will resume tunneling when the maintenance period is complete. The top of Bertha’s cutterhead is located approximately 160 feet below Third Avenue, about halfway between Blanchard and Bell streets. Crews are less than 2,500 feet from the receiving pit near Seattle Center where Bertha will emerge.
Progress updates are posted on Mondays and Thursdays at the Follow Bertha page. You can also follow Bertha on Twitter @BerthaDigsSR99.
