Load Testing of a 117-Year-Old Pile Raft-Paper

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The historic Brooklyn Rapid Transit Powerhouse in New York was redeveloped while preserving its exterior and adapting its interior for new uses. Its 6-foot-thick concrete raft is supported by closely spaced timber piles installed in 1901. Because the redevelopment added substantial loads, the project team evaluated whether the existing foundation could be reused rather than installing new piles—a more costly and disruptive option.<br /><br />A verification program, coordinated with the New York City Department of Buildings, had three parts. Five test pits exposed the timber piles, which were generally sound, with only minor surface softening and no significant damage. Ground-penetrating radar and physical probing identified voids beneath the raft; these were filled by injecting expansive chemical polymer. Finally, two full-scale surcharge tests simulated twice the proposed added design load: 4,000 psf in the former Boiler House area and 1,800 psf in the Turbine Hall. Soil piles provided the loads, while automated surveying tracked raft movement.<br /><br />At peak loading, settlement was approximately 0.3–0.9 inches in the Boiler House area and 0.1–0.3 inches in the Turbine Hall. After unloading, residual settlement was no more than 0.4 and 0.2 inches, respectively. The tests showed that the foundation performed adequately under the proposed loads.<br /><br />Despite challenges—including contaminated groundwater and soil, winter weather, limited interior access, and monitoring-point visibility—the investigation and load tests provided sufficient evidence for approval to reuse the historic pile raft. The approach saved significant time and cost compared with installing new deep foundations, and demonstrated the value of combining pile inspections, void remediation, and full-scale testing when evaluating an unusual existing foundation.

Keywords

Brooklyn Rapid Transit Powerhouse

historic foundation reuse

timber piles

concrete raft foundation

surcharge load testing

ground-penetrating radar

void remediation

settlement monitoring

deep foundation evaluation

New York City Department of Buildings