ROCK SOCKETED DRILLED SHAFTS FOR THE GOETHALS BRIDGE REPLACEMENT-Paper

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The Goethals Bridge Replacement is supported by more than 200 drilled shafts, 4.5 to 10 feet in diameter, socketed into Passaic Formation siltstone. Rock-socketed shafts were selected as a practical, cost-effective foundation solution given the shallow bedrock, heavy bridge loads, and potential for liquefaction and lateral spreading, particularly on the New York approach.<br /><br />Subsurface conditions varied across the alignment. Weathered rock ranged from absent to 16 feet thick, with one location reaching 23 feet, while intact rock quality and strength also varied. Designers used site investigations and load-test results to establish foundation resistances and adapt socket lengths to local conditions. Tests showed that side and base resistance could be mobilized together at compatible displacements. Although measured side resistance exceeded 30 ksf, design values were conservatively limited to 25 ksf in intact rock and 6 ksf in weathered rock; the nominal base resistance for intact rock was 300 ksf. Most shafts met a minimum socket length of two diameters, while weaker or thicker weathered zones required longer sockets.<br /><br />Seismic design on the New York side accounted for reduced lateral support in liquefied sand and lateral-spreading loads from overlying soils. Close coordination between structural and geotechnical engineers was essential to designing for these demands.<br /><br />Construction quality was critical, especially because the design relied on combined socket side and base resistance. Requirements included approved base-cleanout methods, independent inspection, mini-SID measurements to verify sediment cleanliness, cross-hole sonic logging, and detailed construction records. Variable weathered-rock thickness also required flexibility in casing, reinforcing-cage, and socket design.<br /><br />The project demonstrates that thorough characterization, representative load testing, rigorous construction quality control, and design–construction coordination can enable reliable, efficient use of rock-socketed shafts while avoiding unnecessarily deep sockets.

Keywords

Goethals Bridge Replacement

drilled shafts

rock-socketed foundations

Passaic Formation siltstone

load testing

weathered rock

seismic design

liquefaction

lateral spreading

construction quality control