Face time with Bertha: last day above ground for massive tunneling cutterhead

Suspended from a towering crane at the south end of downtown Seattle, the five-story-tall face of Bertha, the world’s largest tunneling machine, spent its last day above ground looking squarely at the old viaduct it was built to replace. Next stop: the 80-foot-deep launch pit where tunneling will start this summer.

Crews working with the Washington State Department of Transportation lowered Bertha’s 838-ton cutterhead into the launch pit today, ending eight weeks of heavy lifting, when crews moved machine parts up to 900 tons each from a ship at nearby Terminal 46 to the bottom of the pit. With the biggest pieces now in position, crews will focus on welding pieces together, connecting wires and hoses and testing the machine prior to its summer launch beneath downtown Seattle.

As Bertha’s owner, WSDOT tunneling contractor Seattle Tunnel Partners, is responsible for ensuring she functions properly at all times. Testing will take about two months and is being overseen by manufacturer Hitachi Zosen Corp. The machine officially becomes the property of STP once it has tunneled approximately 1,000 feet. 

Bertha, who has been updating her progress on Twitter since December, soaked up the moment. “I’ve posed for more photos today than I can count,” @BerthaDigsSR99 tweeted Friday. “I love to smile, but seeing pictures of myself just reminds me that I’m all teeth.”

In addition to assembling and testing the machine, crews are preparing the area near the launch pit for tunneling. That work includes strengthening the soil and building protected work areas along the initial section of the tunnel route, so engineers can perform scheduled inspections of the machine before it begins digging beneath downtown. Meanwhile, work continues near the north end of the Battery Street Tunnel to prepare the area where Bertha will emerge at the end of tunneling.

A 10-foot-long interactive model of Bertha is on display at Milepost 31, the project’s information center in Pioneer Square. Photos of the machine and construction in Seattle are also available on Flickr.