NYCDOT Builds a Bridge Under a Bridge Under a Bridge in Brooklyn-Paper

Paper

Pdf Summary

The New York City Department of Transportation reconstructed the 106-year-old Fifth Avenue Bridge in Bay Ridge, Brooklyn, while maintaining two-way traffic and working around active LIRR and subway tracks, the Gowanus Expressway, existing foundations, and a petroleum pipeline. The south abutment foundations had to be built beneath the existing bridge, with only 12–23 feet of headroom.<br /><br />The work included 18 driven steel H-piles, 24 pipe soldier piles, and 38 micropiles. To suit the restricted workspace, crews installed the H-piles in short sections using a hydraulic impact hammer mounted on a forklift. Temporary starter pits reduced welding and helped remove shallow obstructions. Pile driving and splicing were coordinated to keep work moving.<br /><br />For the micropiles, the team used an approved hollow-bar method instead of the contract’s conventional gravity-grouted bond zone. Continuous grout injection during drilling helped stabilize the borehole, penetrate cobbles, and avoid extracting temporary casing—important advantages in the confined site. Static load tests reached 200 kips in uplift and 240 kips in compression without pile failure or significant displacement.<br /><br />Dynamic testing of the H-piles produced variable capacity results, and some piles required restrikes after waiting for soil setup. The authors note that limited hammer alignment and the use of follower sections may have affected the reliability of the measurements. A refined driving analysis helped relate penetration resistance to the required capacity.<br /><br />All foundation work was completed on schedule without exceeding vibration or deformation limits for nearby infrastructure. The case study emphasizes careful logistics, coordination, and adaptable methods for urban construction. It also recommends considering hollow-bar micropiles early in design and improving H-pile testing procedures in similarly confined conditions.

Keywords

Fifth Avenue Bridge

Brooklyn

NYC Department of Transportation

bridge reconstruction

micropiles

H-piles

pile driving

urban construction

LIRR tracks

hollow-bar method