Contractor announces details of repair work plan for the SR 99 tunneling machine
Bertha, the SR 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, our design-build contractor for the SR 99 Tunnel Project.
STP’s work plan (pdf 4.8 Mb), which is illustrated in a new animation (view on YouTube), 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
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
Bertha is currently stopped approximately 60 feet underground between South Jackson and South Main streets. As owner 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 (pdf 2.5 Mb) crews will use to access and repair the machine.
No Milepost 31 speaker series in July
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