Japanese Hitachi Zosen last week signed the contract to construct the 17.5m-diameter TBM for the Alaskan Way Viaduct Replacement Tunnel in Seattle, USA. The machine will cost the Washington State Department of Transportation (WSDOT) some USD 80M.

“Signing this contract gets us one step closer to taking down the vulnerable Alaskan Way Viaduct,” said Gov. Chris Gregoire. “This state-of-the-art technology allows us to keep SR 99 – and the region’s economy – open for business during construction to replace this critical state highway.”

In July, Hitachi signed a letter of intent with Seattle Tunnel Partners, the WSDOT’s design-build contractor for the tunnel project. The letter of intent allowed the Japanese firm to begin preliminary design of the machine this summer.

By signing the new contract, Hitachi can complete design of the 57.5-foot-diameter machine (17.5m), which will be barged to Seattle and assembled at the south end of downtown in early 2013. The machine will be launched from a pit near the Seattle sports stadiums where crews will begin demolishing the southern half of the viaduct next week. Demolition will require closure of the viaduct for nine days beginning on Oct. 21.

“This will be a truly amazing machine,” state Transportation Secretary Paula Hammond said. “At nearly 60 feet in diameter and more than 300 feet (91m) long, it will be about the same size as some of Washington State Ferries’ largest vessels.”

Seattle Tunnel Partners Project Manager Chris Dixon said, “At any given time there will be up to 40 workers inside operating the machine, monitoring ground conditions, maintaining equipment and working to ensure that tunnelling goes smoothly.”

Later this month, crews will begin utility relocation and other preliminary tunnel work. Excavation of the tunnel launch pit will begin next year, followed by tunnel boring in mid-2013. The USD 1.35 billion tunnel is scheduled to open to drivers in late 2015.