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The world's largest TBM has been at a virtual standstill for more than two years after breaking down. Contractor STP resumed tunnelling yesterday after Washington State Department of Transportation (WSDOT) conditionally lifted the “suspension for cause” that halted activities last month following two safety incidents.
As part of the conditions for lifting the suspension for cause, STP will be permitted to tunnel forward and install approximately 25 concrete tunnel rings. During this time, it must demonstrate that ithave implemented a number of changes to ensure safe progress. These changes include updated tunnel work and quality plans, including calculations of the amount of soil removed during excavation of each tunnel ring. There will also be some personnel changes, new quality assurance protocols and restructured daily tunnelling meetings that include additional participants and protocols.
WSDOT made the decision to conditionally lift the suspension for cause after its team of tunnelling experts evaluated documentation submitted by STP over the past several weeks.
“The contractor has a plan for modifying tunnel operations to ensure positive ground control,” said governor Jay Inslee. “It has also made changes to key personnel, and it has put in place protocols for quality control and assurance. The contractor now has an opportunity to show progress during this test period, prior to tunnelling under the viaduct and underneath Seattle.”
Acting transportation secretary Roger Millar said: “Seattle Tunnel Partners has addressed the issues that led to the suspension for cause. This conditional lift of the suspension for cause will give STP an opportunity to demonstrate the effectiveness of their updated mining procedures. Above all else, this project has always been about safety. We must continue our work to replace the viaduct, but we have an obligation to ensure that work proceeds safely. We will continue to work with STP while taking whatever steps are necessary to protect the interests of the public moving forward.”
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