Downdrag Force Determination by Neutral Plane Method on Driven 24- Inch Prestressed Concrete Square (PSCS) Piles in Coastal Plain Geology-Video

Video Transcription

Video Summary

The presentation covers geotechnical design for the I-64 Hampton Roads Bridge-Tunnel Expansion in Virginia, a roughly $4 billion design-build project. At the Willoughby Bay Bridge abutment, soft, compressible coastal deposits required ground improvement and settlement controls. Because the contractor wanted to build piles before completing surcharge treatment, the team evaluated pile downdrag while allowing construction to proceed quickly.<br /><br />The speakers describe a method based on FHWA’s driven-pile manual to locate the neutral plane by iterating between pile resistance and predicted soil settlement. They assessed settlement at the service limit state and checked downdrag’s structural effect separately. This avoided AASHTO’s prescribed approach of adding downdrag to required pile driving resistance, which the speakers argued can produce uneconomical or unsuitable designs without directly addressing settlement. Instrumentation later confirmed settlement remained within the project’s one-inch limit. The key takeaway is to understand downdrag mechanics and verify both acceptable settlement and pile structural capacity.

Keywords

geotechnical design

I-64 Hampton Roads Bridge-Tunnel Expansion

pile downdrag

neutral plane

ground improvement

settlement control