Final breakthrough for Northgate LRT 08 Sep 2016

Peter Kenyon, TunnelTalk

Final project breakthrough is achieved for completion of the 5.5km of twin running LRT metro tunnels of the US$1.9 billion Northgate Link in Seattle. The second of two refurbished machines procured for the job by the Jay Dee/ Collucio/ Michels (JCM) contractor JV broke through the wall of the retrieval shaft at the University of Washington Station last Thursday (September 1).

Breakthrough at University of Washington Station

In a deviation from the original TBM plan of attack it was the 6.4m diameter Hitachi Zosen EPBM that completed the last of a total six drives between the Maple Leaf portal, near the elevated Northgate Station, will be located, and the retrieval shaft at the underground University of Washington Station (Fig 1).

A machine breakdown suffered by the Robbins EPBM approximately two-thirds of the way into the second of its three scheduled drives – between Roosevelt Station and U-District Station – resulted in delayed completion of that section.

The 10-week breakdown – which ended with the restarted but still damaged Robbins EPBM limping into U-District Station at the end of its second drive – has sparked a court battle between the Ohio-based machine manufacturer and JCM over the standard of the refurbishment prior to its delayed launch in January 2015. The Hitachi Zosen machine launched in June 2014, more than six months ahead of the Robbins EPBM.

Fig 1. Northgate Link and stations
Fig 1. Northgate Link and stations

Following an assessment of the damage suffered by the Robbins machine, JCM decided to transport the Hitachi Zosen EPBM – which had by then already completed the last of its three scheduled drives – back to U-District Station for relaunch on its fourth and the project’s final drive.

According to the contractor’s original TBM schedule for the Northgate Link excavation, the Robbins machine should have completed final project breakthrough – at the end of its scheduled third drive – in March (2016). In the event the Hitachi Zosen machine achieved this milestone, some five months later than originally planned.

Attention on the US$440.3 million Northgate Link underground construction contract now shifts to completion of the 23 cross passages, tunnel fit-out, and M&E, which are scheduled for completion in 2018. Construction works for the underground stations at U-District and Roosevelt are due to begin next year (2017), with work on the elevated Roosevelt Station beginning in the fall of this year (2016). The Northgate LRT line - which connects with the recently opened University Link LRT at University of Washington Station – is expected to enter service in 2021.


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