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Mon April 12 2021

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Tunnelling set to resume in November on stalled SR 99 project

20 Jul 15 Contracting joint venture Seattle Tunnel Partners has submitted a new schedule for completing tunnelling on the SR 99 project, which has been at a standstill since the TBM broke down more than 18 months ago.

Bertha is under repair
Bertha is under repair

The contractor’s revised timeline shows tunnelling resuming in late November. The machine is due to emerge approximately one year later at the north end of the Seattle’s downtown area.

This week, Seattle Tunnel Partners began installing a new main bearing on the Bertha, the TBM that has been at a standstill in the US city since late 2013. Tunnelling was halted after the machine overheated. Investigations showed damage to the seal system and established that it needed to be replaced along with the main bearing.

The SR 99 tunnel is now scheduled to open to drivers in spring 2018, according to a revised schedule that STP submitted to Washington State Department of Transportation. Machine repairs are scheduled be completed in the autumn. STP and manufacturer Hitachi Zosen will then perform an extended series of tests to ensure the machine is ready to complete the tunnel drive.

“The contractor’s schedule has changed, but the contract that governs their work remains the same,” said Todd Trepanier, WSDOT’s Alaskan Way Viaduct replacement programme administrator. “The state is a paying customer in this transaction, and we’re intent on getting what we contracted for. We will continue to protect taxpayers and hold the contractor responsible for their work as they deliver this vital project.”

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Since lifting the front end of the machine from the ground in March, STP has fully assessed the disassembled machine parts and made significant repairs and enhancements. In addition to beginning installation of the main bearing, STP crews have installed portions of the new seal system that will protect the bearing. Modifications include the addition of reinforcing steel, new monitoring systems and upgrades to the soil-conditioning system to prevent clogging.

“Fully disassembling and assessing the machine was always the key to determining how long the repairs would take,” said Chris Dixon, Seattle Tunnel Partners project manager. “We want to reassemble the machine and resume tunneling as quickly as possible, but we also want to ensure the repairs are done right.”

While the machine has been under repair, STP has continued work at the future tunnel portals, including construction of ramp and highway connections, and the buildings that will house tunnel operations.

STP crews halted tunneling in December 2013 after the machine overheated. After an investigation, they discovered damage to the seal system and determined it needed to be replaced along with the main bearing. The cause of the damage has not been determined. Responsibility for costs associated with the delay will be determined through the process outlined in the tunnel contract.

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