Alaskan Way Viaduct Replacement Update – August 2013

bertha3Bertha begins: digging officially underway in Seattle

This time, there were no crowds or fanfare. It was just Bertha, the world’s largest tunneling machine, finally getting the chance to do what she was built to do: dig. 

Bertha got her first taste of tunneling on July 30, officially starting the 2-mile journey beneath downtown. Early in the afternoon, Bertha’s 5-story-tall cutterhead broke through the north wall of her 80-foot-deep launch pit. She’s expected to emerge in about 14 months near the intersection of Sixth Avenue North and Harrison Street.

Crews working with the Washington State Department of Transportation will push forward slowly at first, digging about 6 feet per day. By the time the machine is beneath downtown, she will dig up to 35 feet per day.

The tunnel route is divided into 10 separate zones, each with its own underground landscape. In the first zone, crews strengthened or replaced fill soils dumped there by the city’s early settlers while building protected areas where they can inspect the machine.

“We designed the project so that we would have opportunities to test the machine and make sure she’s functioning properly before we get beneath downtown,” said Linea Laird, WSDOT administrator for the Alaskan Way Viaduct Replacement Program. “If Bertha was learning to ride a bike, this initial section would be her training wheels.”

To track Bertha’s progress, visit the Follow Bertha Web page and follow her on Twitter: @BerthaDigsSR99.

Milepost 31 speaker series – tracking Bertha’s progress beneath downtown

Join us for this month’s speaker series to learn what Bertha will encounter as she digs through different types of soil, passes beneath other tunnels, and digs as deep as 200 feet beneath downtown.


Thursday, Aug. 1

6 to 7 p.m.

Milepost 31

211 First Ave. S., Seattle

Admission is free.


After the talk, be sure to leave enough time to explore the rest of the First Thursday Art Walk in Pioneer Square. Milepost 31 is open Tuesdays through Saturdays from 11 a.m. to 5 p.m., and stays open until 8 p.m. on First Thursdays. Free parking is available for First Thursday art walk patrons in Pioneer Square. Please visit for information about participating garages.