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00000181-fa79-da89-a38d-fb7f2a000000Bertha, the world's biggest tunneling machine, is a five-story-tall monstrosity of drilling tasked with digging out the tunnel for State Route 99 to replace the Alaskan Way Viaduct. It's journey to the center of the earth underneath downtown Seattle began in July 2013, and since then the project has seen its fair share of successes and failures.Follow the progress of the $3 billion megaproject with KUOW.

Letter From Engineers Raises Serious Concerns About Bertha

A transport vehicle carries the new front end of the bearing block for Bertha. First though, the machine has to be dug out from beneath Pioneer Square.
Flickr Photo/WSDOT (CC-BY-NC-ND)
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A transport vehicle carries the new front end of the bearing block for Bertha. First though, the machine has to be dug out from beneath Pioneer Square.

They were not reassuring words.

Engineers hired to rescue Bertha, the deep boring machine stalled under downtown Seattle, wrote to state officials: “If we continue the current ‘repair as we go’ method of excavation, we significantly increase the risk of a catastrophic failure.”

This hypothetical situation is from a draft letter from Brierley Associates, the firm hired to dig out Bertha from beneath Pioneer Square. At a Seattle City Council meeting on Monday, state officials said it was dramatically out of context – they worried that releasing too much information about Bertha would result in a culture of panic.

Bertha is not in danger of catastrophic failure, state officials said emphatically. They said the boring drill’s rescue just needs close monitoring – because pressure is more intense at 74 feet below sea level.

“Repair as you go” means digging first, then injecting cracks with grout later. The other method is to inject grout into the cracks of the pit before excavation.

State officials expressed frustration with city officials at the council meeting – and discussed limiting city officials’ access to the database from which they plucked this draft letter. 

Bertha was named for Bertha K. Landes, Seattle's first (and only) female mayor. Elected mayor in 1926, her motto was "municipal housecleaning."