WSDOT Report: Budget OK, Schedule Impacts Likely Due to TBM Stoppage

TBM Featured News According to a report by an expert review panel released Feb. 27, the Washington State Department of Transportation (WSDOT) expects the Alaskan Way Viaduct Replacement Program, which includes the SR 99 tunnel, to be successfully completed within current budget, although likely with a delay in the schedule.

According to the document, the stoppage of the TBM likely will push back tunnel completion past the Dec. 31, 2015, date proposed by the joint venture contractor, Seattle Tunnel Partners (STP), but earlier than the contract performance date of Nov. 13, 2016.

That delay is based largely due to issues with seals on the TBM’s main bearing. The machine was initially stopped on Dec. 6 and STP spent much of December reducing water pressure in the ground around the machine in order to inspect the excavation chamber and look for objects that might be blocking the machine’s path.

On Jan. 2, contractor crews successfully reduced water pressure enough to visually inspect a portion of the excavation chamber. A piece of an 8-in. diameter steel pipe could be seen protruding through an opening in the machine’s cutterhead. The steel pipe is a well casing installed in 2002 following the 2001 Nisqually earthquake to help geologists characterize groundwater behavior in the area.

Following completion of inspections, crews re-started the machine on Jan. 28, pushing 2 ft to complete the tunnel ring that was in progress on Dec. 6. At that time, high temperature readings were encountered again, and the machine was shut down again for further evaluation. On Feb. 7, it was reported that damage to the seals protecting the main bearing were discovered.

The 57-ft diameter TBM, the world’s largest, had advanced about 1,200 ft along the 1.7-mile alignment before being stopped. The $3.1 project – including the $1.44 billion tunnel under downtown Seattle – comprises replaces the aging seawall, rerouting SR 99 into the tunnel, and demolishing the existing elevated highway.

The TBM, manufactured by Hitachi Zosen in Japan, had experienced issues with main bearing during testing prior to shipping, but was repaired and passed all tests prior to launch.

The full report can be found here: http://www.wsdot.wa.gov/Projects/Viaduct/Media/Default/Documents/Final%20ERP%20Report%20February%202014.pdf

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