Going Deep at 39th Avenue, Queens, NY

GEODesign is providing geotechnical engineering services to F&T Group and Shanghai Construction for the Tangram development project located at 133-21 39th Avenue in Flushing, New York.

The site occupies nearly two blocks between 37th & 39th Avenues and between Prince Street & College Point Boulevard in the downtown Flushing neighborhood of Queens. The project is a mixed-use complex with approximately 1.4 million square feet, including retail space, underground parking for more than 1,100 vehicles, two residential towers, an office tower and a boutique hotel, each 15 stories.

The main geotechnical feature of the project is going deep with four levels of below grade space, excavating 55 feet down and 30 feet below the groundwater. The project originally included a very costly support of excavation (SOE) and foundation system, which was designed by others.

GEODesign developed a more cost effective and efficient SOE and foundation system, resulting in more than $2 million of savings.

The massive excavation required the use of several SOE solutions including secant pile walls with multiple tieback levels, rakers and struts, soldier pile and lagging walls with up to 6 tieback levels, and pit underpinning with tiebacks. In total, over 1000 hollow bar tiebacks are included in the design.

Most notably, the SOE included the installation of over 800 linear feet (in plan) of 30″ diameter secant piles to support four adjacent buildings. A combination of pretensioned tiebacks and preloaded rakers were used to provide temporary lateral support to the 40 foot high secant pile walls. Once the building is constructed, the secant piles will remain as part of the permanent foundation wall.

GEODesign is providing construction support services, including full-time inspection of the SOE system. This continued involvement is extremely beneficial to the client because we are able to quickly respond to inevitable unanticipated field conditions, by revising existing designs and implementing new techniques, as required. This comprehensive approach results in a pragmatic and constructible system.

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