Urban High Capacity Deep Foundation Solutions in Sites with Complex History and Geology-Paper

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The paper presents the investigation, design, and construction of high-capacity foundations for a ramp providing heavy-truck access to New York City’s East 91st Street Marine Transfer Station, with an alternative alignment studied at 92nd Street. The site’s reclaimed waterfront history, buried debris, remnants of an old bulkhead, variable bedrock elevations, and proximity to buildings and busy roads created significant challenges.<br /><br />Subsurface exploration included eight borings, rock cores, a test pit, pavement cores, and groundwater monitoring. Ground-penetrating radar helped identify possible utilities and the buried bulkhead. Fill and loose soils overlay mica schist bedrock, generally encountered 20–42.5 feet below ground.<br /><br />Driven piles were unsuitable because of obstructions, vibration risks, and nearby structures. Instead, designers selected rock-socketed drilled shafts for the overwater foundations, where lateral loads were higher, and minipiles for the land-based ramp, where access and space were constrained. Permanent steel casing stabilized the holes, while down-hole hammers were used to drill the rock sockets.<br /><br />An Osterberg-cell load test was conducted on a production shaft, an approach suited to the limited space and overwater location. The test applied a maximum sustained bidirectional load of 907 kips and measured shaft resistance and displacement. Results supported the design assumptions of 160 ksf ultimate end bearing and approximately 28.8 ksf ultimate unit skin friction.<br /><br />Key construction lessons included the importance of early obstruction detection, sufficient borings to characterize changing bedrock elevations, and equipment suited to sloping rock. Noise and vibration monitoring helped limit impacts on neighboring structures and residents. The case demonstrates how detailed site investigation, local geological knowledge, and collaboration between designers and contractors can enable reliable foundations in complex urban settings.

Keywords

drilled shafts

minipiles

rock-socketed foundations

Osterberg-cell load test

marine transfer station

East 91st Street

bedrock elevation

subsurface exploration

urban waterfront

heavy-truck ramp