Washington State DOT, Partners Announce SR99 Tunnel Machine Repair Plan

AASHTO Journal, 20 June 2014

Washington State Department of Transportation joined Seattle Tunnel Partners this week to announce specifics in the plan to repair Bertha, the world’s largest tunneling machine tasked with digging the State Route 99 Tunnel under Seattle.

The machine, which is creating the tunnel as part of the Alaskan Way Viaduct Replacement Program, was placed in the ground last summer with the hope of opening the new tunnel in late 2015. Bertha abruptly halted digging in December and WSDOT reported that the seal system protecting the machine’s main bearing was damaged. Officials announced in April that STP intended to excavate the pit July through September so that in October it can begin repairing the machine. STP planned on testing the machine post-repair in February and to resume digging in March.

According to WSDOT and STP officials, who released Bertha’s repair plan on Monday, STP will take the following steps to getting Bertha back to work: replace the damaged seal system with a tougher one; replace the main bearing; install better monitoring systems; and add steel to make the machine stronger and accommodate the new seal system. STP will also improve the soil conditioning injection system, extend the length of the agitator arms in the mixing chamber, and widen the openings at the center of the cutterhead to ensure Bertha’s effectiveness. An animated video demonstrating the work on Bertha is available here.

“We are encouraged Seattle Tunnel Partners is taking these steps to repair and enhance the machine,” Todd Trepanier, WSDOT administrator for the Alaskan Way Viaduct Replacement Program, said in a statement. “Once we have additional information from STP, we will analyze it alongside our independent tunnel experts. It is STP’s responsibility to meet their milestones and supply a machine to deliver the tunnel.”

Additional information on the Alaskan Way Viaduct Replacement Program is available here.

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