Porous limestone bedrock, rising sea levels, and a high water table made placing the foundation for an underground parking garage just blocks from the beach quite a challenge. That's where Miami Beach, Florida, is building its new, 153,000-square-foot cultural center, a two-building complex consisting of a cylindrical structure that houses gathering spaces and a cube that houses a hotel and meeting rooms.

Layton Construction is a general contractor with 10 offices nationwide that self-performs its concrete work. Its Orlando, Florida, office tackled the problem by creating a dry "bathtub" for crews to work in. The contractor determined the most economical way to form the workspace, which is 22 feet below street level, would be a combination of steel sheet piles and a 40,000-square-foot unreinforced tremie-placed slab.

Placement via tremie is used when other methods aren't possible; jobsite staging space is too small or, as the case here, submerged in water. Self-consolidating concrete was pumped through vertical or near-vertical steel pipes into the form. As the form filled, the concrete surrounded the pipe's delivery end, which kept water from getting into the pipe as it was raised for each successive lift. This method enables concrete contractors to place large volumes at deep locations in a short amount of time with the added advantage of eliminating air pockets.

The slab consumed about 6,000 cubic yards of concrete. Police had to redirect traffic because ready-mix trucks were at the site pumping concrete into two tremie pipes for almost two consecutive days. Divers were employed to place concrete at the bottom of the excavation and, once the slab cured, pump out the water and mud from the concrete and steel sheet-pile bathtub. Once the water was cleared out and the bathtub was dry, work could commence on the rest of the building.