Tunnel-boring machine Big Bertha shut down for “months” due to complexity of needed repairs
Wayne Grayson | February 11, 2014
What Big Bertha leaves behind. Two workers walk through the first rings of tunnel dug by Big Bertha in October.

What Big Bertha leaves behind. Two workers walk through the first rings of tunnel dug by Big Bertha in October. Credit: WSDOT Flickr

Washington State Department of Transportation officials say Big Bertha, the world’s largest tunnel-boring machine, is likely out of commission for months.

An inspection conducted after the machine overheated in late January found that several cutterhead openings were clogged with dirt along with considerable damage to seals around the machine’s main bearing, according to a report from komonews.com.

Bertha's massive cutterhead. Credit: WSDOT Flickr

Bertha’s massive cutterhead. Credit: WSDOT Flickr

WSDOT officials announced that removing the clogs and replacing the seals will take months to complete as it is “a complicated process.”

In fact, the contractor in charge of the dig, Seattle Tunnel Partners, is still trying to figure out how to get access to the seals in order to replace them. They’re currently in communication with Bertha’s manufacturer to figure it out, but right now their options include going through the back of the machine, or digging an access shaft reaching from the surface to the front of the machine.

Bertha has completed one-tenth of the 1.7-mile State Route 99 tunnel below Seattle, which will carry a double-deck highway. The new tunnel will replace the SR 99 Alaskan Way Viaduct.

This is the second major setbaack to Bertha’s progress. After nearly two months of downtime caused by the machine hitting a steel pipe, she advanced four feet near the end of January only to be brought to a halt due to a warning light being triggered in the control room that signals overheating.

Temperatures reached 140 degrees near the cutter head which is about 1 1/2 times what’s normal.

It’s unclear whether the months of downtime will affect the projects $3.1 billion price tag. Digging the tunnel along will cost $2 billion.


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