Willis Avenue Swing Bridge: Design and Construction of Drilled Shaft Foundations

Abstract

Drilled shaft foundations are currently being constructed to support selected piers of the new, four lane, 106 meter long Willis Avenue Swing Bridge and approach structures. The Willis Avenue Swing Bridge over the Harlem River is being replaced under a $612 million project which is the largest ever undertaken by the Movable Bridge Group of the New York City Department of Transportation. Drilled shafts vary in diameter from 1220 mm to 1524 mm and extend into bedrock which is composed of Inwood Marble or Fordham Gneiss. The design capacity of the drilled shafts was estimated from the side resistance within the rock socket, discounting any side resistance above the rock socket in accordance to empirically derived methods outlined in the AASHTO Bridge Design Specifications. The design capacity of the drilled shafts is in the process of being verified by means of an Osterberg Cell static load test conducted on four instrumented test shafts representing each drilled shaft size and each type of bedrock on the Bronx side of the project. The load test results suggest that empirical design methods combined with field rock properties data underpredicted the drilled shaft capacity in reported bedrock.