Subterranean in Seattle

If walls could talk, well, we would be hearing a lot during May and June at the New Arena at Seattle Center.
But in this extraordinary case of delivering a world-class facility to Seattle sports fans and entertainment lovers of all blends, passersby won't even be able to see those walls. Let New Arena construction executive Ken Johnson explain, with an assist (hockey term alert!) from NHL Seattle CEO Tod Leiweke.

"Everything inside has been removed [from the KeyArena version], including seats, railings, concession stands, acoustic panels, you name it, all gone," says Johnsen, a Seattleite who brings a full and contagious measure of enthusiasm to this project every day. "We just started pile-drilling [a less noisy cousin of boom-boom-boom pile-driving] this month for two purposes.
"One is to build a wall that holds up the outside of our excavation when we started digging down in the dirt. The wall frames and secures the hole that will hold the new bowl of seats and the playing surface."

Johnsen says the second purpose of the pile-drilling "relates to the temporary steel going up" to hold the existing landmark roof in place above-ground. The roof, which weighs 44 million pounds, the public will see walking or driving by the construction site.
"It's an entire and brand-new arena except for the roof," says Johnsen. "As Tod [Leiweke] likes to say, it's subterranean. When fans approach a typical arena, they see a massive building. Here you will come in the upper concourse. It will be exciting to look down and see the lower bowl and ice level at first glance."
So those walls going up this month and next, if this was a conventional project, we would see them rising from the Seattle Center plaza?
"Exactly," says Johnsen.

As the pile-drilling continues in May, what's called the "hard demolition" will commence.
Here's the process: Starting with the northeast quadrant of the lower bowl, heavy machinery will "pull down, bash up, chop up and crumble" the concrete that formerly supported seats, gates, concourses, the playing floor and more. As that concrete comes down and hauled away, workers will start building that part of the wall. The heavy machinery moves on to the northwest quadrant and repeats the "hard demo" in a circle until all lower-concrete is removed and support walls constructed. Then the process is repeated for the upper-bowl concrete-all while "shoring" with temporary support steel for the iconic roof is achieved simultaneously.
"We will get international attention [from the engineering, architectural and construction industries]," says Johnson. "People will want to see it, know how we did it all going on at the same time."
Come early June, the "major excavation" excavation phase will begin.

"Right now, we are hauling off concrete," says Johnsen. "June is when we start on the dirt."
The major excavation is when "we dig down into the earth" for the additional 15 feet needed for the world-class arena bowl. The new depth will be 53 feet below ground or more than five stories. Plus, the new bowl will widen underground and those news walls will require an even deeper level of support, up to 70 feet below ground in the corners.
Only fitting, since hockey coaches frequently remind their players the game on the ice is won in the corners.