The world's largest-diameter tunnel borer, designed by a Spanish company, is to be transported this month from Japan to Seattle, Washington, to build a replacement tunnel for a viaduct badly damaged in a 2001 earthquake.

Measuring 17.5 meters (57 feet) in diameter - equivalent to the height of a six-story building - and 112 meters in length and weighing 7,000 tons, the machine designed by Spanish company Dragados, a contractor for Spanish civil engineering group ACS, will drill a new tunnel under that northwestern U.S. city.

The new road will replace the State Route 99 Alaskan Way Viaduct, Washington state's main north-south corridor, which was severely damaged in the February 2001 Nisqually earthquake

Dragados USA and joint-venture partner Tutor-Perini Corporation were awarded the contract for the more than $1.36 billion tunneling project.

Dubbed "Bertha" in honor of Bertha Knights Landes, mayor of Seattle from 1926-1928 and the first mayor of a major U.S. city, the machine was manufactured by Japan's Hitachi Zosen in Osaka.

Projections are that the machine, which is due to be transported later this month by ship in pieces weighing 900 tons each and arrive in Seattle in late March, will be able to dig the 2.8-kilometer (1.7-mile) tunnel in less than 14 months.

Once in Seattle, the tunnel borer will be reassembled and tested before excavation work begins, likely in early June.

The Alaskan Way Viaduct Replacement Program is a partnership between the Federal Highway Administration; the Washington State Department of Transportation; the Port of Seattle, which relies heavily on the SR 99 corridor and has contributed $300 million to the program; and other public agencies. EFE