Highway tunnel project starts in Seattle

SEATTLE — After years of planning and months of work, the world’s largest tunnelling machine started drilling Tuesday to create a new route for Highway 99 under downtown Seattle buildings, the Washington Transportation Department said.

The tunnel will go under about 200 buildings, but officials don’t expect any serious problems from the machine they call Bertha.

“We know exactly the path of Bertha and what she’ll encounter along the way,” spokeswoman KaDeena Yerkan said.

The tunnelling crew will be monitoring for settling and vibrations and is prepared to keep building foundations secure.

Transportation officials have set up Bertha with her own Twitter account to provide updates.

Bertha is about 100 metres long and weighs 7,000 tonnes. It will leave a tunnel nearly 18 metres in diameter.

The $80-million machine is part of the $3.1-billion project to replace the Alaskan Way Viaduct, the double deck highway along the downtown Seattle waterfront. Built in 1953, it has carried 110,000 vehicles a day. Officials said the structure had to be replaced because it could collapse in an earthquake. Its removal is part of a project to renovate the waterfront, rebuilding the seawall, improving surface streets and adding new vistas of Elliott Bay.

It will take about 14 months to complete the tunnel, which will be about 3.2 kilometres long.