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World's biggest TBM faces further delays while fix is devised

10 Feb 14 Two contributing factors have been identified for the stoppage that has kept the world’s largest TBM out of action for two months. A fix must now be found.

Engineers investigating the problems have found a clogged cutterhead and high-temperature readings that indicate there are other factors to explore.

The TBM is being used by Seattle Tunnel Partners (STP) - Dragados USA and Tutor Perini - on Washington State Department of Transportation’s SR 99 Tunnel Project. WSDOT and STP have identified.

A tweet published on Friday by the TBM, called Bertha, said: "It's too early to say how long the stoppage will last and who's responsible for the cost".

Tunnel workers performed 158 hours of hyperbaric inspections between in January. They found that many of the cutterhead openings were clogged with dirt and other material. It had previously been thought than a major obstruction may have been affecting the performance.  

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After the cutterhead was unclogged, the contractor moved the machine forward an additional two feet and installed one of the concrete rings that line the tunnel.

However, higher-than-normal heat sensor readings were measured, which had also been the case on the day tunnelling  had to be halted in December.

In the course of investigating the temperature readings, STP discovered damage to the seal system that protects the tunnelling machine’s main bearing. Investigations have shown that portions of the seal system have been damaged and need to be repaired or replaced. The project team is working with the machine’s manufacturer, Hitachi, to determine the best fix for this issue. They are currently assessing the extent of the damage and the best path forward.

STP is the design-build contractor of the project and the TBM is owned by STP. It is STP’s responsibility to determine the scope of the issue and the best options to repair it and get the machine moving again.  

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