FEATURE ARTICLE Luxury Living on the Beach in Coney Island, Brooklyn Near the western tip of Coney Island, two towers, 20- and 22-stories, with a 3- to 5- story podium-garage are being constructed across an entire city block at 3514 Surf Avenue in Brooklyn, N.Y. Appropriate subsurface investigations and load testing are essential for the success of any deep foundation design, and their importance is further emphasized when complex soil and groundwater conditions must be considered during a fast-track design schedule. Numerous challenges arose during the design and construction phases of this project, including complex soil conditions, strict settlement tolerances, aggressive design and construction schedules, and post-Hurricane Sandy flood considerations. To meet strict project settlement tolerances, the geotechnical and structural engineers proposed a hybrid foundation system of deep pile foundations at the towers and spread footings at the podium-garage. Mul t iple rounds of subsurface explorations and pile load testing were performed during design and early construction to optimize the foundations. The subsurface investigation and load testing programs for this project exceeded the minimum requirements of the local building code, and the results and obtained data allowed the design team to fine-tune a cost-effective foundation design and reduce construction schedule. Through cooperation among the project stakeholders (geotech- nical engineer, structural engineer and pile driving contractor), the final pile type, size, splicing details and driving criteria were selected using the extensive field data, all of which demonstrated the value that a vigorous testing program can have for a project with complex site conditions. Site Description The site, approximately 70,000 sq ft (6,500 sq m) in plan area, consists of an entire block near the western tip of Coney Island, and is bordered by the Riegelmann Boardwalk to the south. Proximity to the boardwalk and Coney Island beach was a significant attraction for the site developer but added several complexities for the site development. Environmental, Surveying, Landscape Architecture, and Geology The site falls within the 100-year flood zone, Special Flood Hazard Area AE (Preliminary FIRM for City of New York), with a design flood elevation (DFE) of 12 ft (El. 3.66 m), with respect to the North American Vertical Datum of 1988 (NAVD88). In addition, the closest documented U.S. Geological Survey high-watermark during Superstorm Sandy (2012) was El. 11.5 ft (El. 3.5 m). Therefore, the ground floor slab for all livable spaces was raised above the DFE, and the ent i re development was flood-proofed to El. 12 ft (El. 3.66 m) to meet the flood design requirements. Development Description The new development includes a 3- to 5-story podium and garage that occupies most of the site, and two towers (22 and 20 stories) on the northwest and northeast corners of the site, respectively. The foundation loads for the podium-garage and towers vary significantly. For the podium-garage, the column loads range between 80 and 415 kips (356 and 1,846 kN) AUTHORS Miguel G. Matos, P.E., Tasos G. Papathanasiou, P.E., and Marc J. Gallagher, P.E., LEED AP, Langan Engineering, DEEP FOUNDATIONS • SEPT/OCT 2018 • 89
