In Seattle, assembly of the mammoth 57.5ft (17.52m) Hitachi Zosen EPB machine ‘Bertha’ has begun in earnest, following the completion of the 80ft (24.5m) deep SR-99 Alaskan Way Tunnel TBM launch pit on Sunday (May 12). After nearly a year spent building secant pile walls, removing soil and assembling the infrastructure required to support the near 7,000-ton machine.
Last spring, a field of unturned earth marked the spot where Bertha will begin excavation of the 1.7-mile (2.7km) long highway tunnel beneath downtown Seattle. One year and 86,000 cubic yards of excavated muck later, the completion of the launch pit clears the way for machine assembly. ‘Bertha’s’ 41 elements are now being lowered into the launch pit using a custom fabricated Barnhart Crane modular lift tower mounted on a traveling gantry.
Once assembly and testing of the five-story-tall, US$80 million, machine is complete, Seattle Tunneling Partners’ (STP JV) – a design-build consortium comprising Dragados-USA, Tutor Perini and HNTB – will begin excavation on Washington State Department of Transportation’s (WSDOT) US$1.35bn double-deck tunnel this summer.
“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, Malcolm Drilling crews drilled more than 200 piles, up to 100 feet deep into the ground to form the pit’s walls. The perimeter of the pit is 80 feet wide and 400 feet 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 next to the head wall.
Work is also under way near the north end of the Battery Street Tunnel to prepare the area where Bertha will emerge at the end of tunneling.