Design Specifications for the Static and Seismic Design of Piles for Downdrag

The AASHTO Load and Resistance Factor Design (LRFD) Bridge Design Specifications (2012) recognize that piles in settling soil experience downdrag forces from negative skin friction and that they may also move downward with the adjacent soil. Many bridges are constructed in areas where there is compressible soil, or liquefiable soil which necessitates the consideration of downdrag forces and associated settlement. Downdrag for static conditions, as well as seismic conditions, has increasingly placed greater demands on existing and new foundations and also led to higher construction costs. In addition, experience has shown that there are significant cost advantages to the use of the neutral plane method due, in part, to differences with the approach that is currently explicitly described in the AASHTO Specifications. The objective of the research is to develop design specifications for the Static and Seismic Design of Piles for Downdrag that will use the framework of the AASHTO specifications and incorporate the most up-to-date research on drag load. The neutral plane method will be explained in detail, and its use will be illustrated by real-world examples. According to transportation engineers from several states, experience with the explicit AASHTO approach for downdrag has shown that it can lead to unrealistic results and the use of longer piles, surcharging, and/or ground modification. The AASHTO Specifications allow the use of the “neutral plane method,” although it is only briefly referenced. The absence of detailed guidelines for the neutral plane is a reason cited for the reluctance among designers and consultants to use the neutral plane method even though the neutral plane method represents a simple, more realistic model for piles subjected to a downdrag force and its associated effects.

Language

  • English

Project

  • Status: Proposed
  • Funding: $500000
  • Contract Numbers:

    Project 12-116

  • Sponsor Organizations:

    American Association of State Highway and Transportation Officials (AASHTO)

    444 North Capitol Street, NW
    Washington, DC  United States  20001

    National Cooperative Highway Research Program

    Transportation Research Board
    500 Fifth Street, NW
    Washington, DC  United States  20001

    Federal Highway Administration

    1200 New Jersey Avenue, SE
    Washington, DC  United States  20590
  • Project Managers:

    Dekelbab, Waseem

  • Start Date: 20180619
  • Expected Completion Date: 0
  • Actual Completion Date: 0

Subject/Index Terms

Filing Info

  • Accession Number: 01672544
  • Record Type: Research project
  • Source Agency: Transportation Research Board
  • Contract Numbers: Project 12-116
  • Files: TRB, RiP
  • Created Date: Jun 18 2018 3:03PM