Langan Engineering, New York City
Numerous challenges arose during the Avalon Brooklyn Bay project, including high building loads, strict settlement tolerances, poor soil conditions, proximity to a New York City Transit station on a soil embankment, fragile neighboring buildings, and aggressive construction deadlines. While a mat foundation could have withheld the structure’s weight, predicted settlements on the native loose-to-medium sands were high enough to render this conventional solution detrimental.
The solution to limit excessive total and differential settlements and keep construction costs low was to design a deep foundation system that could support the entire building weight. Specifically, the engineering team designed a unique hybrid system combining different pile types extending to various depths. With this design, the total weight of the building would be uniformly distributed through the raft to the piles and then to the sands below. The final foundation design consisted of a combination of drilled micropiles and driven piles with varying lengths and capacities. The engineers designed and implemented a meticulous index-pile program to observe the field performance of these piles and optimize the foundation design.