Abstract:
The 130-year-old Park Avenue Viaduct is an elevated steel structure carrying four third-rail-powered tracks, with approximately 750 trains per day operating into Grand Central Terminal. Originally constructed in 1893 and rehabilitated in 1993, the viaduct is being fully replaced between 2024 and 2027. The new structure improves long-term resiliency and is being constructed using a rapid phased approach to minimize service disruptions, with the existing viaduct remaining operational while new foundations were installed beneath it.
The project was divided into two phases, located between East 115th and East 123rd Streets and between East 127th and East 132nd Streets in Harlem, NY. The foundation system consisted of rock-socketed drilled micropiles installed in low overhead conditions, requiring innovative construction techniques while minimizing impacts to the surrounding infrastructure.
The foundation work was a collaborative effort between Halmar International as prime contractor, Hardesty & Hanover (H&H) as the geotechnical engineer, and Keller North America, Inc. as the geotechnical contractor. Over 1,000 rock-socketed micropiles using 16-inch diameter casing were installed utilizing the Mincon “Spiral Flush†casing advancement system to address challenging subsurface conditions and optimize constructability. In several locations, drilling occurred within one foot of active sensitive utility lines, requiring specialized protective measures and foundation layouts to ensure the utilities remained undisturbed.
A defining challenge of the project was its execution under low headroom conditions, with a maximum clearance in some areas of 13 feet, combined with hard rock drilling. These constraints required specialized equipment and strategies to maintain safety and production efficiency. The quality assurance program included verification testing on sacrificial micropiles, proof testing at each substructure location, and rock socket video inspections for every installed micropile. This project highlights the team’s innovative approach to complex geotechnical challenges, showcasing advanced drilling systems, strategic planning, and efficient execution under constrained conditions.