Starting in the early morning hours of Saturday, contractors plan to pour 400 truckloads of concrete to build a 10-foot-thick foundation mat for Comcast's new skyscraper in Center City.
Officials say it will be one of the largest concrete pours in Philadelphia history.
The mat will attach the building's core to bedrock.
The Comcast Innovation and Technology Center will be the city's tallest skyscraper, at 1,121 feet. The Comcast Center next door, opened in 2008, stands 975 feet.
Concrete contractor B. Pietrini & Sons, of King of Prussia, says 50 concrete trucks will make the 400 deliveries.
Company President Fran Pietrini tells The Philadelphia Inquirer it's "a dream job" that, despite the size, could be done in less than 12 hours.
You can watch Saturday's pour and the ongoing construction of the Center City skyscraper on our Comcast Tower Cam.