Reaching nearly 15 m (50 ft) and located three stories below sea level, the 425-car garage for Sunny Isles Beach, Florida’s Jade Signature condominium will be the deepest ever built in the low-lying region.
A first-of-its kind subterranean parking garage, set on the very edge of the Atlantic Ocean in porous limestone and sand, it is a central element of the development, which features a new 55-story luxury condominium.
Innovative construction methods, 3200 tons of steel rebar, and one of the largest concrete pours in the history of South Florida all ensure the garage foundation, or concrete mat, remains dry—and stands out as an important engineering success.
Designed by Herzog & de Meuron, Jade Signature was envisioned to offer resort living, anchored by a beach-level pool area that naturally flows into the lobby, with three full floors of amenities above. This open, beach-living concept could only be realized by ‘sinking’ the parking garage out of sight. Such an approach contrasts sharply with the typical condominium in South Florida, which tend to feature a pool area situated atop several parking levels—usually all above the lobby. To create the underground structure, the development, design, and building teams worked closely together to determine the best method for subterranean construction in close proximity to the ocean.
After extensive research and planning, Suffolk Construction determined a deep-soil-mixing construction method would be used to create a giant waterproof ‘bathtub’ that protects a concrete mat above the tub from groundwater. This concrete mat forms the base of the garage. Engineers from Malcolm Drilling Company designed the bathtub, and created a 2.7-m (9-ft) paddle bit with a hollow core and hybrid mixing auger, specially designed for the project’s deep soil mixing process.
The giant high-torque drill began the process of creating the bathtub in September 2013 by boring into the site’s crushed limestone, while simultaneously injecting cement binder slurry, or grout, into the ground. Crushed limestone and sand served as a natural aggregate that created the fresh concrete-like material that hardened into the bathtub’s solid walls. The limestone between the bathtub walls was then crushed by the drill’s bullet-teeth-laden auger. To allow for an easier excavation and to use less cement, water was used as the drilling fluid until the mixing tool reached the measured depth which corresponded to the top of the bathtub floor. At this point, more cement slurry was injected and mixed with the limestone to create the actual floor.
Once the tub was created, auger cast pilings were drilled 45 m (149 ft) into the ground to support the tower, and to hold down the floor of the tub during construction. The loose-mix soil inside of the tub was then excavated to reveal the new, waterproof underground form—a step that occurred over a three-month period completed in early November 2014.
With the tub complete and emptied, the massive concrete mat at the base of the garage was constructed, with more than 10,058 m (33,000 ft) of concrete poured non-stop by 1200 deliveries over the course of nearly 24 hours on January 2, 2015. Today, as construction of the Jade tower continues, the garage mat remains entirely dry.
By employing the deep-soil-mixing technique, the Jade team solved the tremendous problem of building underground in porous soil only 30.5 m (100 ft) from the ocean. As planned, the process stopped water intrusion into the garage area altogether, allowing for the quicker excavation of dry material from the site, which streamlined the construction process. At the same time, the bathtub approach promises to keep the site entirely dry as the condominium begins to rise. Completion of the tower and garage is expected in mid-2017.