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Seattle TBM’s 2,000-Ton Front End Reconnected with Dramatic Crane Lift

Lowering the SR 99 tunneling machine’s front end back into the access pit

Company info

310 Maple Park Avenue SE
P.O. Box 47300
Olympia, WA
US, 98504-7300

Website:
www.wsdot.wa.gov

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Seattle Tunnel Partners (STP) has reconnected the SR 99 tunneling machine’s 2,000-ton front end to the section that remained in the access pit during repairs. With the two sections of the machine now bolted together, crews from Mammoet have unhooked the front-end piece from the massive red crane that performed last week’s lift.

The effort to return the tunneling machine's front end to the 120-foot-deep access pit began early Monday morning. Crews started by vertically lifting the piece, which includes the machine’s cutterhead, motors and the new main bearing assembly. The crane then moved horizontally on its rails to the north. When the piece was above the pit, crews rotated it to a semi-vertical position and lowered it partway into the pit before breaking for the evening. Work resumed early Tuesday morning, with the piece reaching the bottom of the pit Tuesday afternoon.

After the machine has been reassembled, STP and manufacturer Hitachi Zosen will conduct a series of tests will follow reassembly to ensure the machine is ready to resume mining.

Bertha, the massive machine responsible for digging the SR 99 tunnel beneath Seattle, is the largest machine of its kind in the world. Tunneling beneath Seattle allows us to replace the SR 99 Alaskan Way Viaduct while minimizing closures of the highway during construction. When the tunnel opens, a two-mile stretch of SR 99 will move underground, allowing us to remove the viaduct and clear the way for new public space along Seattle's downtown waterfront.  

In December 2013, STP stopped tunneling approximately 1,000 feet into the tunnel drive after measuring increased temperatures in the tunneling machine. While investigating the cause of the high temperatures, STP discovered damage to the machine’s seal system and contamination within the main bearing. STP is working to repair the seal system and replace the main bearing so that crews can resume tunneling.