gallons per minute. We had recently completed the St. Regis Bal Harbour for the Starwood Corporation, which featured a one-story, fully below-grade parking garage, which covered 300,000 sq ft (28,000 sq m), with deeper, core areas extending to 20 ft (6 m) below the water table. The project team included Coastal, Baker Concrete, Thompson Pump, and HJ Foundation. We completed construction to these depths without a bottom plug or tremie, but instead employed a vast array of pumps and a quarry’s worth of gravel —maxing out at 42 large diesel pumps at peak—to depress the water table for 13 months. In addition to installing, fueling and constantly repositioning our pumps, water discharge was a tremendous challenge, making our logistics like a chess game, never opening more ground than we could maintain. Our firm was all ears when the opportunity to work on Key Biscayne with a new system presented itself. New Urbanism “New Urbanism” is the term applied to the planning movement currently shaping development codes nationwide. According to Better Cities and Towns, if New Urbanism can be boiled down to a single idea, it might be making places “walkable.” Another of the movement’s goals has been to conceal parking. Sherri Gutierrez, project director for Oceana as well as vice president and office director at Arquitectonica, (the project architect) agrees. She says that many municipalities have re-examined their zoning codes in an effort to create better urbanism and toward re-inventing the pedestrian realm. As a result, ground floor area becomes priceless, forcing developers to look into below-grade parking. She points to projects such as Oceana in Key Biscayne and Brickell CityCentre in Miami. Several subcontractors have looked for creative solutions to build underground in “the dry.” Below-grade parking may very well become the new norm, says Gutierrez. From the development side, developer Corti says that as long as the cost of the product can justify it, below-grade parking can turn 200,000 sq ft (18,580 sq m) of above-grade parking area into an attractive pedestrian area. From a purely practical standpoint, Goldstein, of KACO, adds “as 60 • DEEP FOUNDATIONS • MAR/APR 2013 developable land has become less available, the use of basements has become more of a necessity.” In late 2009, Consultatio Real Estate acquired a 10 acre (4 ha) site on Key Biscayne. Initially, the below grade parking garage—in this case mandated as a condition of approval for the project—was to feature a sheet pile perimeter, with an augercast pile foundation, in combination with a tremie plug, facilitating construction of a hydrostatic slab. By late 2011, the steel sheets were on-site and pending permitting, construction was ready to commence. It was at this point that DeSimone introduced Corti to the Layne/Bencor team. Bencor is a slurry wall specialist and subsidiary of Layne Geoconstruction. At the same time, Consultatio brought Coastal Construction aboard to manage the construction. plug and the walls) was very attractive. The plugs are environmentally sustainable since the virgin soil material is cemented in place and a concrete cylinder is produced. These cylinders are placed one against the other to create a continuous bottom plug to seal the bottom against ground water intrusion. In addition, the team devised a separation wall bisecting the project, allowing excavation and construction of the tower to proceed in advance of the garage. The Layne team further proposed to install a test hole to full depth—at their own risk—consisting of jet grout walls and base, to prove the viability of their proposal. Corti set the condition that if upon excavation he could press a piece of tissue paper to the wall and it didn’t stick, the job was theirs. Layne quickly mobilized, jet grouted the test area, and after a cure time, excavated the hole. On Tower construction of Oceana showing excavation Corti was highly impressed by Layne executives’ proposal to encircle the entire tower and garage with a slurry wall and barrette system—the barrettes supporting perimeter columns—and infill the entire footprint with a jet grout plug, on which large spread foundations would rest. The jet grout plug would serve as the water seal as well as the interface between the spread foundations and the rock below. He thought that the monolithic nature as well as the similarity of materials (between the March 21, 2012, with all the teams’ stakeholders assembled, Corti, along with the design team and engineers from Layne descended the ladder into what most described as the deepest hole they had ever seen in Florida. Corti pulled the tissue from his pocket, pressed it to the wall, and it fell to the ground. Florida Engineering, the excavation subcontractor, had excavated a smaller hole immediately adjacent to show the natural water table, less than 3 ft (1 m) from the surface. Layne
