Dive summary:

• A boring machine that is 326 feet long and 57.3 in diameter is en route from Japan to attack everything Seattle can offer, including water-filled soils, glacial tills, tough clays and boulders.
• The machine will create a two-level tunnel beneath downtown Seattle so that the state can eventually take down the 1950s-vintage Alaskan Way Viaduct that carries the elevated State Route 99 north and south next to the waterfront and takes its name from the street underneath it.
• Seattle Tunnel Partners, the consortium formed for the project, will have up to 600 workers pushing the project along for 20 hours a day, five days a week, so it can finish in 2015,a year ahead of the state Department of Transportation's schedule.

From the article:

"It's a $1.4 billion job, and it involves boring the world's largest-diameter tunnel to date.... It's very geologically complex." ...