Contractor details repair work plan for SR 99 tunneling machine

Seattle — Bertha, the State Route 99 tunneling machine, has always been big. The focus now is on rebuilding Bertha and making her better, according to a new repair work plan unveiled Monday, June 16, by Seattle Tunnel Partners, the Washington State Department of Transportation’s design-build contractor for the SR 99 Tunnel Project.

STP’s work plan, illustrated in a new animation, contains four major repair and enhancement elements:

• Replacing the damaged seal system with a more robust system
• Replacing the main bearing
• Installing enhanced monitoring systems
• Adding steel to strengthen the machine and accommodate the new seal system

Other major enhancements of the work plan include:

• Widening the openings at the center of the cutterhead
• Improving the soil conditioning injection system
• Installing bit- and wear-resistant steel on the cutterhead
• Extending the length of the agitator arms in the mixing chamber

“We are committed to the success of this project,” said Seattle Tunnel Partners Project Manager Chris Dixon. “We’re confident these repairs and enhancements will enable this machine to successfully tunnel beneath downtown Seattle. We won’t resume tunneling until we’re certain Bertha is up to the task.”

STP will provide WSDOT with additional supporting information about rebuilding the machine in the coming months, in accordance with the design-build contract, to demonstrate how the repairs will meet the contract’s performance and technical requirements, including:

• An analysis demonstrating that the machine’s structure can withstand all loads from the surrounding ground and its own operation
• Seal design details and background calculations
• Design of revised conditioner injection systems and cutterhead openings
• Updated operations plan including enhanced instrumentation and monitoring for key machine components
• Complete testing program for all modified machine components prior to restart of mining

“We are encouraged Seattle Tunnel Partners is taking these steps to repair and enhance the machine,” said Todd Trepanier, WSDOT’s administrator for the Alaskan Way Viaduct Replacement Program. “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.”

The SR 99 tunneling machine is currently stopped approximately 60 feet underground between South Jackson and South Main streets. As owners of the machine, STP is responsible for ensuring it functions properly at all times. STP is currently building the underground walls of a circular pit crews will use to access and repair the machine. Viewers can watch the access pit take shape on a newly installed time-lapse camera.

For more information about the SR 99 Tunnel Project, part of the Alaskan Way Viaduct Replacement Program, visit www.alaskanwayviaduct.org.