Abstract:
The New York City Housing Authority (NYCHA) Redhook Housing was subjected to damage during Superstorm Sandy. As a result, the NYCHA has an on-going project known as Restoration Associated with Sandy Recovery Program to improve the overall long-term sustainability of the existing development to increase resistance against future storms. The specific project included 28 residential buildings and several service buildings within the Red Hook Development in Brooklyn, New York. The subsurface conditions within the eastern portion of the site included existing fill material underlain by varying stratums of very loose, loose and medium dense silty sands to depths ranging between 65 to 80 feet below the ground surface; followed by very soft to medium stiff clay or dense silty sands. The subsurface conditions within the western portion of the site included existing fill material, very loose to medium dense silty sands and organic clayey silts to depths of 60 feet; underlain by very soft to medium stiff sandy silts. Based on the geotechnical report and bid package for the site, a conventional driven steel pile system was specified containing two pile depths. The 45 foot driven pile was designed to have a capacity of 68 kips compression and 25 kips tension. The 120 foot drive pile was designed to have a capacity of   200 kip compressive, 60 kip tensile, and 20 kips lateral. As part of the project bidding, an alternative pile type was recommended and analyzed to provide quicker installation, reduce vibrations, reduce noise, and relatively largecost savings. The alternative consisted of a drilled helical displacement pile. Due to relatively high lateral loading, an innovative method of using a double steel casing within the upper 20 feet of the drilled helical displacement pile was constructed. Theoretical calculations were followed by in-situ static compression, tension, and lateral load tests. The load testing demonstrated higher pile capacities than theoretically determined. The field testing proved the piles capable of the required project capacities and the use of drilled helical displacement piles as the best alternative for the project and accepted by the NYCHA. This paper discusses the theoretical calculations of capacity, installation, and load testing results of the  drilled helical displacement piles to minimize cost and optimize construction.