Shanghai Tower is a super-tall building currently under construction in Shanghai's Pudong district. It broke ground in November 2008, and it's on schedule for completion in 2014. The surprising thing? It's yet to rise above the ground. So: what's going on in that enormous hole in the ground? Technical Director Dick Fencl and Project Architect Howe Keen Foong offer their insights, including noting that the giant circular form above isn't a hole; it's a slurry wall. And it's temporary. Here's the story behind it.

Fencl explains, "There are two key slurry walls that will be built for this project. The first, a giant circular form that you see here and in the images above, is temporary. It's put in place to excavate down to the level where we build the mat-slab foundation.  Once the mat-slab foundation is finished, this temporary slurry wall will be removed.

"The second slurry wall (yet to be built) will line the perimeter of the entire site. It will be permanent, and it's a key element of top-down construction. Slurry walls are a good construction method for sites with high water tables, such as Shanghai."

A key component of Shanghai Tower's structure is its six-meter-thick (nearly 20 feet) mat-slab foundation. Howe Keen Foong offered up some staggering stats on the process (pictured above), explaining: "it was poured in a single, continuous, 60-hour concrete pour. Construction crews poured an average of 1,000 cubic meters (35,300 cubic feet) of concrete per hour. The effort required orchestrating roughly 120 concrete trucks per hour for a total of 61,000 cubic meters (2,154,200 cubic feet) of concrete."

What did this mean for construction crews on the ground? In the image above, you see workers standing atop rebar reinforcements that will be part of the mat-slab foundation. To complete the process, Foong reports that more than 2,000 workers operating 405 trucks and 19 cement pumps worked in two shifts for more than 60 consecutive hours to complete the pour. They accomplished the feat seamlessly, and to great acclaim--the building's developer hosted a well-attended ceremony to celebrate this spectacular construction milestone.

Richard Fencl is a Principal at Gensler, and Technical Director for our North Central region. Dick loves to talk building technology, and delights in explaining concepts ranging from the best way to create a water resistant building envelope (harder than it looks) to why we place concrete—we never pour it! Got a question about the best way to detail a building? Contact him at richard_fencl@gensler.com.