FEATURE ARTICLE Foundation Innovation in Florida Aerial view of the foundation construction for the Oceana in Key Biscayne, Fla. (photo credit smithaerialphotos.com) Underground garages and basements have long been avoided in South Florida construction. Most major construction is within a stone’s throw of the ocean (or its little sister Biscayne Bay), and most builders are challenged by extremely high water tables and extremely pervious soils. Newly enacted zoning regulations calling for concealed parking provide further challenges. The Oceana project in Key Biscayne, Fla., was conceived in such circumstances. The project is a 16-story high-rise tower that houses 142 luxury condominium units, sitting astride an underground, 2-story parking garage. The tower and garage footprints are 38,000 sq ft (3,530 sq m) and 72,000 sq ft (6,700 sq m), respectively, and the excavation reaches down 17 ft (5.2 m) below the water table. Consultatio Real Estate Inc. is developing the project, under the leadership of architect Marcos Corti. According to Vincent DeSimone, chairman of DeSimone Consulting Engineers of Miami, the project’s structural engineer, “Recent code changes in Miami make it prohibitive to use available floor area above grade for parking because that use reduces revenue producing floor area. Until the advent of these code changes, there was little incentive to go deeper than a one-story below-grade parking level. The few attempts to park two levels below grade resulted in lawsuits and spotty success.” DeSimone was one of the chief proponents of what became the foundation system at the Oceana. His firm, working with Layne Geoconstruction, had worked at The Cosmopolitan of Las Vegas, building a concrete wall around a five-level subterranean parking garage. The perimeter walls were founded on a dense limestone layer that created a seal against groundwater migrating upward. A hybrid version of this approach proved to be the winning design for the Oceana project. Florida Geology The vast majority of South Florida high- rise buildings in the last 30 years have employed an almost identical script: augercast piles and pile caps, wellpoint AUTHOR John Mills, General Superintendent, Coastal Construction DEEP FOUNDATIONS • MAR/APR 2013 • 59 dewatering, occasional sheet piling, supporting a building in which a lower level of parking is either depressed only slightly into the earth, or more commonly positioned alongside the main tower. Barry Goldstein, P.E., is the principal engineer and president of KACO, the project’s geotechnical engineer. He says, “The Florida geology is uniquely suited for augercast piles. The immature limestone is relatively weak in nature and allows for drilling with a continuous flight auger. This, in combination with the limestone’s inherent porous structure allows for significant load transfer from a cast-in- place pile.” This porosity carries a cost. Goldstein says this porous structure is what allows for permeability and very high water flow into excavations. Dewatering by conventional means can be performed only to certain depths as the volume of water required to be pumped, even in a small excavation, can exceed tens of thousands of gallons per minute. Our firm, Coastal Construction, had experienced that tens of thousands of
