Performance of an Osterberg Cell (O-Cell) Load Test on a High-Capacity Production Drilled Shaft at the Kosciuszko Bridge

摘要

The Kosciuszko Bridge, the first cable-stayed bridge in New York City, carries a 1.8 km (1.1 mile) segment of the Brooklyn-Queens Expressway (I-278) over Newtown Creek between Morgan Avenue in Brooklyn and the Long Island Expressway interchange in Queens. The project was carried out in 2 distinct phases: Phase I for the design and construction of the east (or Queens) bound structures and Phase II for the design and construction of the west (or Brooklyn) bound structures. In both phases, foundations for the main tower pier consisted of 55 m (180 foot) long high-capacity drilled shafts, with a 2 m (6.5 foot) diameter, 4 m (13 foot) long rock socket. In order to meet the accelerated schedule without impacting the quality of the bridge, bidirectional Osterberg Cell (O-cell) load tests were performed on production shafts. Under such conditions it was necessary to tailor the test performance criteria to production shaft requirements, namely the maximum test load on one hand had to be high enough to demonstrate the required compressive and tensile resistances, on the other hand it had to be limited as not to cause concrete cracking or permanent shaft deformations. This paper focuses on the O-cell test performed for Phase II and includes a discussion on shaft performance inferred from test results, shaft installation process, geotechnical instrumentation, and data acquisition details. Comparison between results of O-cell load test performed in Phase I and Phase II is also provided.