Brooklyn Beachfront Towers in a Post-Super Storm Sandy World

Located near the western tip of Coney Island, 3514 Surf Avenue includes two 20- and 22-story towers, a three- to five-story podium, and an attached garage. This paper describes the numerous challenges that arose during design and construction, including complex soil conditions, strict settlement tolerances, aggressive design criteria, and flood concerns magnified by Hurricane Sandy. High-foundation loads under the towers, combined with a deep compressible clay layer [65–105 ft (20–32 m) below grade], would have resulted in unacceptable settlement of the towers if shallow foundations were used. However, the relatively light garage loads did not present settlement issues and therefore did not warrant expensive pile foundations. To address differential settlement between the towers and garage, the geotechnical and structural engineers proposed a hybrid foundation system of pile foundations under the towers and spread footings under the garage. The interaction and settlement at the interface of the two foundation types were considered while designing this cost-effective solution that satisfied serviceability requirements. Multiple rounds of subsurface explorations (16 test borings, 11 CPT probes, and 22 test pits), index-pile driving (20 piles), and pile load testing (40 PDAs, 22 CAPWAPs, five compression load tests, and three lateral load tests) were performed during the design phase to optimize the foundations. The project team considered different pile types and sizes during the index-pile program as recommended by the geotechnical engineer and foundation contractor.