Silver Star Motors "Tackles" Brownfield Site and Adjacent NYCT Subway-Paper

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The Silver Star Motors project in Long Island City, Queens, involved constructing a 100,000-square-foot, 10-story mixed-use building with a cellar, Mercedes-Benz showroom, and rental apartments on a Brownfield site.<br /><br />Excavation extended about 15 feet through impacted soil, below the groundwater level and beneath neighboring foundations. The site was only seven feet from an active NYCT subway station, and the excavation support system came within inches of a large sewer. More than 200 feet of adjacent structures required underpinning.<br /><br />The project used a combination of drilled micropile soldier piles, timber and precast-concrete lagging, underpinning piers, soil anchors, and inclined rakers supported by a partially constructed foundation mat. Dewatering and groundwater-related subgrade disturbance added complexity. The design team also coordinated approvals with transit and environmental agencies while adapting to construction changes and tight tax-credit and remediation deadlines.<br /><br />Monitoring included an Automated Motorized Total Station, prisms on neighboring structures and soldier piles, automated seismographs within the subway, and manual surveys. Underpinning settlement was generally negligible, with a maximum of 0.35 inches in one isolated area. Recorded subway vibrations remained below 0.2 inches per second, and NYCT did not require a post-construction condition survey.<br /><br />Environmental work included site investigations, remediation planning and oversight, air monitoring, and management of contaminated soil. Remediation was completed three days before the November 2015 deadline; the Certificate of Completion was received in December.<br /><br />Lessons included ensuring adequate dewatering before underpinning, maintaining stabilizing soil berms until rakers are installed, and planning for the need to construct and cure mat sections before rakers can be supported. The project also demonstrated the value of responsive design coordination, timely monitoring, and drilled micropiles in constrained urban sites.

Keywords

Silver Star Motors

Long Island City

Queens

mixed-use building

brownfield site

micropile soldier piles

underpinning

subway station proximity

dewatering

environmental remediation