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Thu March 04 2021

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Details set out for repair of giant TBM

18 Jun 14 Details of the repair plan for the world’s biggest tunnel boring machine (TBM) have been set out by the design-build contractor for the SR 99 tunnel project in the US state of Washington.

STP’s work plan, which is illustrated in a new animation (see below), contains four major repair and enhancement elements to bring the TBM – called Bertha – back into use. Bertha has been at a standstill since December.

The key aspects of the plan are:

  • 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 centre 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 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.

The work plan has been set out in an animation available on YouTube:

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