Working With Bertha Gives New Meaning to 'Confined Space'

June 30, 2016

Over the next several weeks, seven 5-member crews will work around the clock to complete routine cutterhead maintenance at the front end of Bertha, the SR 99 tunneling machine. To safely do this, crews must stabilize the ground in front of the machine. They do this by injecting a type of clay, known as bentonite, into the front end of the machine. This creates a seal that prevents water and soil from entering – and air from escaping – their work space.

Next, crews over-pressurize the space by introducing compressed air which pushes against the bentonite to counteract the ground and water pressure at the front end of the machine. This newly created hyperbaric work space has pressure levels that are higher than regular atmospheric pressure, similar to conditions found in an underwater dive.

New videos from the Washington State Department of Transportation provide views of what it is like for workers on the Alaskan Way Viaduct project.

The video below shows the chambers crews use to adjust to hyperbaric conditions and enter the space behind the cutterhead.

The video below was provided by Ballard Marine Construction, the firm responsible for completing this work on the tunnel project. It shows crews at work behind Bertha’s cutterhead during a planned maintenance stop earlier this spring.


Justin Costello, a hyperbaric division manager with Ballard Marine, said workers can only enter the site once per day and need at least 18 hours between compressions.

Source: WSDOT; Geekwire