Kosciuszko Bridge Main Pylon Foundation Deep Foundation Solution-Paper

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The Kosciuszko Bridge’s main pylon was founded on eight large-diameter drilled shafts extending through about 160 feet of overburden into Gneiss/Schist bedrock. The Design-Build team developed construction methods and an Alternate Technical Concept (ATC) to reduce cost and schedule while meeting NYSDOT requirements.<br /><br />Construction faced contaminated near-surface soils, buried concrete obstructions, very hard bedrock, and rock slopes far steeper than pre-bid borings had indicated. The team isolated contaminated soils and groundwater with temporary casings, removed and treated materials appropriately, and enlarged the overburden excavations to allow the rock to be leveled and permanent casings seated. Concrete plugs sealed the casing-to-rock interface, enabling reverse-circulation drilling of the rock sockets. Shaft alignment, socket cleanliness, and concrete integrity were checked using Sonicaliper profiling, Mini-SID inspection, Crosshole Sonic Logging, and Thermal Integrity Profiling.<br /><br />The accepted ATC replaced a sacrificial demonstration shaft with a production shaft tested using the Osterberg Cell “Chicago Method.” This allowed the socket’s end bearing to be tested to ultimate stress while side shear remained at service-level loading. A separate lateral-load test demonstrated consistent performance, approximately 0.5-inch head movement at 350 tons, and a lateral influence depth of about 60 feet.<br /><br />All shafts were completed within specified tolerances, without ground loss or shaft collapse. The project showed how early constructability planning, collaboration, and tailored testing can manage unforeseen subsurface conditions and deliver schedule and cost benefits.

Keywords

Kosciuszko Bridge

drilled shafts

gneiss schist bedrock

alternate technical concept

reverse-circulation drilling

Osterberg Cell test

lateral load test

contaminated soils

crosshole sonic logging

construction methods