Permanent Markers

Here's the dirt about the dirt at the New Arena at Seattle Center: The digging and hauling of 600,000 cubic yards is nearly complete.
"Last September, we started digging the hole," says Ken Johnsen, construction executive for Oak View Group and NHL Seattle. "Our goal was to reach a point where we could start putting in the concrete [permanent pilings] by early 2020. That's happening and we are about 90 percent done with hauling the dirt. We should be finished by mid-March."

Those permanent concrete pilings will reattach the y-columns and buttresses that were severed by a water-jet machinery to allow digging out the gigantic rectangular subterranean footprint (53 feet deep at center ice level) of the New Arena. In concert with the cutting of the y-columns, temporary steel columns were erected to hold up the landmark roof.

For the next few months, the process will reverse. Those temporary steel columns will be removed as the concrete pilings are sunk into the ground and constructed upward, starting with a rebar (steel caging) framework that will reattach to the rebar left sticking out of the cut columns and buttresses. There is careful engineering in how the rebar is structured and weaved together; individual workers climb the framework to connect the rebar as designated, followed by a construction engineer who will inspect and subsequently approve the work when it meets standards.
"That rebar needs to be just right," explains Johnsen.
The final step for the pilings is to pour concrete in, around and over the rebar. It takes about four to five pours (each batch of concrete needs to set first) to complete the job. Currently, there are three such permanent pilings in final stages located in the northeast quadrant underneath the iconic roof, with several more under construction.

Once those permanent pilings are secure and helping support the roof, then the nearby temporary steel columns can be removed. The feat requires supremely planned engineering to take away the temporary steel without disturbing the roof.
"It is a critical, well-thought-out dance," says Johnsen. "As careful as we were to cut the columns and buttresses without affecting the roof, we have to be just as careful removing the temporary steel columns."
Sometime in summer, the permanent pilings will be holding the roof without any of the temporary steel. In the shorter term, the dirt removal is nearly done with last loads dug up underneath a former temporary ramp used by hauling trucks. The sum is an early glimpse of what's to come for fans in 2021, such as imagining the first puck at center ice where the larger central temporary column now stands. "We're starting to get a sense of, hey, this is how this arena's going to feel," says Johnson.