Hydraulic Performance of Shallow Foundations for the Support of Vertical-Wall Bridge Abutments

This study combined abutment flume experiments with numerical modeling using computational fluid dynamics (CFD) to investigate flow fields and scour at vertical-wall abutments with shallow foundations. The focus was situations dominated by flow contraction in the bridge opening, turbulence around the bridge abutments, and variations in bed roughness and cross-section geometry resulting from riprap apron installation at the streambed elevation. When riprap aprons are installed flush with the bed, the gap between the two abutment aprons is exposed to increased bed shear stress on the unprotected erodible channel bed in the gap, leading to greater contraction scour depths than would have occurred without the aprons. All riprap aprons installed flush with the streambed for abutment protection are vulnerable to movement of rocks at the edge of the apron (edge failure) because that edge lies within the contraction scour zone. Contraction scour may increase movement of rocks at the edge of the riprap apron. Contraction scour in the gap at the edge increases as the opening becomes narrower and the riprap coverage on the channel bed increases. Edge failure is of concern because riprap apron protection of shallow foundations is an integrated structural element of the bridge that must perform throughout the design life of the bridge. This study had two phases. The first phase focused on flume abutment clear-water experiments using erodible uniform bed material to investigate different riprap installation geometries. The experiments facilitated evaluation of various field installations as well as the performance of installations based on the design guidelines from "Bridge Scour and Stream Instability Countermeasures," Hydraulic Engineering Circular No. 23. The experiments also supported development of new riprap apron guidelines to address apron durability. In the second phase, a conceptual model was developed to define the flow-riprap interaction to inform development of design guidance. A CFD modeling approach was applied to validate the conceptual model and to support recommendations for riprap apron installation. This study supports the significant recommendation that locating the top of the riprap apron at the level of the estimated contraction scour depth should be preferred to surface installations. This buried apron would reduce vulnerability to edge failure. A buried apron might also be preferred from an environmental perspective because the riprap apron would be covered by natural streambed material.

• Record URL:
  https://www.fhwa.dot.gov/publications/research/infrastructure/structures/bridge/17013/17013.pdf
• 
• Record URL:
  https://rosap.ntl.bts.gov/view/dot/35916
• Corporate Authors:

  Genex Systems, LLC

  2 Eaton Street, Suite 603
  Hampton, VA  United States  23669

  Federal Highway Administration

  1200 New Jersey Avenue, SE
  Washington, DC  United States  20590
• Authors:
  • Suaznabar, Oscar
  • Huang, Chao
  • 0000-0002-6034-8637
  • Xie, Zhaoding
  • Shen, Jerry
  • Kerenyi, Kornel
  • Bergendahl, Bart
  • Kilgore, Roger
• Publication Date: 2017-2

Language

• English

Media Info

• Media Type: Digital/other
• Edition: Laboratory Report
• Features: Appendices; Figures; Photos; References; Tables;
• Pagination: 128p

Subject/Index Terms

• TRT Terms: Bridge abutments; Experiments; Fluid dynamics; Flumes; Hydraulics; Mat foundations; Riprap; Scour; Turbulence
• Subject Areas: Bridges and other structures; Highways; Hydraulics and Hydrology;

Filing Info

• Accession Number: 01632257
• Record Type: Publication
• Report/Paper Numbers: FHWA-HRT-17-013
• Contract Numbers: DTFH61-11-D00010-T-5009
• Files: TRIS, ATRI, USDOT
• Created Date: Apr 11 2017 4:41PM