SR 99 Tunnel Launch Pit Complete

Last spring, a field of unturned dirt marked the spot where Bertha will begin digging the two-mile State Route 99 tunnel beneath downtown Seattle. One year and 86,000 cubic yards of soil later, it’s a pit fit for the world’s largest tunneling machine.

Crews finished building Bertha’s 80-ft-deep launch pit on Sunday after nearly a year spent building its underground walls, removing soil and building the infrastructure needed to support the nearly 7,000-ton machine. Its completion clears the way for tunneling to start this summer, once Bertha’s 41 pieces have been reassembled and tested at the bottom of the pit.

“If Bertha is the star of the project, the launch pit is her stage,” said Linea Laird, Washington State Department of Transportation administrator for the Alaskan Way Viaduct Replacement Program. “Completing the launch pit means we’re that much closer to the start of tunneling.”

Launch-pit construction started last summer in the work zone west of Seattle’s stadiums. Before excavation began, crews drilled more than 200 piles as many as 100 ft into the ground to form the pit’s walls. The perimeter of the pit is 80 ft wide and 400 ft long.

Assembly of the machine started at the south end of the pit shortly after it arrived last month from Osaka, Japan. Now that the front end of the pit is complete, crews have started building the body of the machine near the spot where it will first push into Seattle’s soil.

Crews are also preparing the surrounding area for tunneling, including strengthening the soil and building protected work areas along the initial section of the tunnel route so they 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.

For more information about the SR 99 Tunnel Project, visit www.alaskanwayviaduct.org.

Source: Washington State Department of Transportation.