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

PPT Presentation

Pdf Summary

The presentation examines downdrag on driven 24-inch prestressed concrete square piles in coastal plain geology, using the neutral plane method. It reviews the project conditions, settlement analysis, resistance curves, and established guidance, including the 2014 AASHTO LRFD Bridge Design Specifications and the 2016 FHWA driven-pile manual. A historical trigger for considering downdrag is post-driving ground-surface settlement exceeding 0.4 inches.<br /><br />The project analysis estimates an unfactored drag force of 183 kips. The presentation also reports a total pile-head settlement of approximately 0.8 inches.<br /><br />The main conclusion is that downdrag should be treated as a load for structural strength checks, but it does not reduce geotechnical strength. Pile-head movement from downdrag should instead be assessed in the geotechnical service limit state. The authors recommend updating the AASHTO approach to align with this distinction in the FHWA method. They also suggest refining the FHWA procedure by using T-Z curves to estimate mobilized skin friction and comparing soil–pile displacement along the pile with the settlement profile.

Keywords

downdrag

driven piles

prestressed concrete piles

neutral plane method

coastal plain geology

settlement analysis

AASHTO LRFD

FHWA driven-pile manual

drag force

T-Z curves