Tunnel: Bertha gets her bearings

WSDOT says the contractor digging the tunnel will likely replace the boring machine's entire main bearing
Crosscut archive image.

Bertha's cutting head has run into troubles.

WSDOT says the contractor digging the tunnel will likely replace the boring machine's entire main bearing

The repairs to Bertha, the Highway 99 Tunnel boring machine, will likely be more extensive than originally planned, a Washington State Department of Transportation official said on Thursday. 

Seattle Tunnel Partners, the contractor digging the underground roadway has told WSDOT "verbally" that they are going to replace the machine's main bearing, according to Todd Trepanier, a program administrator for the department. 

Until now, the contractor has only said that it would replace a set of damaged seals that protect the bearing. For weeks, Seattle Tunnel Partners has not confirmed whether the bearing itself might have been damaged by grit or water when the seals failed.

Manufactured by the German company Rothe Erde, the roughly 88-ton, 33-foot diameter bearing allows Bertha's 57.5-foot wide "cutter-head" to spin and bore through the earth. The machine's entire bearing assembly costs $5.1 million, according to project budget documents. A replacement bearing is in Japan and will be shipped by boat to Seattle along with other parts, Trepanier said. 
Some Rothe Erde bearings come equipped with monitoring systems and have measuring devices. WSDOT told Crosscut in early March that neither were installed on Bertha. 

The machine is currently stopped near South Main Street, under Pioneer Square. It has barely moved in the last 117 days. 

Bertha was first idled in early December after encountering increased resistance while digging. Seattle Tunnel Partners detected the bearing seal problems in late January.

The contractor has been working with the machine's manufacturer, Hitachi Zosen Corp., on plans to partially unearth and repair the tunneling rig. That operation will involve excavating an 83-foot diameter, 120-foot deep circular pit in between the Alaskan Way Viaduct and Pier 48, south of South Main Street. Before digging can begin, WSDOT and Seattle Tunnel Partners are awaiting the results of an archeological survey that is required to meet Federal Highway Administration cultural preservation guidelines.

Crosscut archive image.

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