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REPORT
This report is an archived publication and may contain dated technical, contact, and link information
Publication Number:  FHWA-HRT-17-013     Date:  February 2017
Publication Number: FHWA-HRT-17-013
Date: February 2017

 

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

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FOREWORD

Vertical-wall bridge abutments with shallow foundations may present unique contraction scour issues in cases where the bridge opening is narrow and riprap aprons are used to protect the abutment from abutment scour. In addition, new approaches to abutment designs that feature non-rigid construction techniques require investigation to ensure they are constructed to protect against undermining. This report describes a study of methods for evaluating bridge abutments to assess their vulnerability and provides design guidance for their application. The study was conducted at the Federal Highway Administration’s Turner-Fairbank Highway Research Center J. Sterling Jones Hydraulics Laboratory. The report will be useful for engineers and other technical personnel involved with designing, constructing, and inspecting vertical-wall bridge abutments.

Cheryl Allen Richter, P.E., Ph.D.
Director, Office of Infrastructure
Research and Development

Notice

This document is disseminated under the sponsorship of the U.S. Department of Transportation in the interest of information exchange. The U.S. Government assumes no liability for the use of the information contained in this document. This report does not constitute a standard, specification, or regulation.

The U.S. Government does not endorse products or manufacturers. Trademarks or manufacturers’ names appear in this report only because they are considered essential to the objective of the document.

Quality Assurance Statement

The Federal Highway Administration (FHWA) provides high-quality information to serve Government, industry, and the public in a manner that promotes public understanding. Standards and policies are used to ensure and maximize the quality, objectivity, utility, and integrity of its information. FHWA periodically reviews quality issues and adjusts its programs and processes to ensure continuous quality improvement.

 

Technical Report Documentation Page

1. Report No.

FHWA-HRT-17-013

2. Government Accession No. 3 Recipient's Catalog No.
4. Title and Subtitle

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

5. Report Date

February 2017

6. Performing Organization Code
7. Author(s)

Oscar Suaznabar, Chao Huang, Zhaoding Xie, Jerry Shen, Kornel Kerenyi, Bart Bergendahl, and Roger Kilgore

8. Performing Organization Report No.

 

9. Performing Organization Name and Address

Genex Systems, LLC
2 Eaton Street, Suite 603
Hampton, VA 23669

10. Work Unit No. (TRAIS)

11. Contract or Grant No.

DTFH61-11-D00010-T-5009

12. Sponsoring Agency Name and Address

Federal Highway Administration
1200 New Jersey Ave., SE
Washington, DC 20590-9898

13. Type of Report and Period Covered

Laboratory Report; October 2013–July 2016

14. Sponsoring Agency Code

 

15. Supplementary Notes

The Contracting Officer’s Technical Representative was Kornel Kerenyi (HRDI-50). Nathan Tsou assisted with the literature search.

16. Abstract

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.

17. Key Words

Contraction scour, Abutment scour, Riprap apron, Vertical-wall abutment, Narrow bridge opening, Shallow bridge foundation, Buried riprap

18. Distribution Statement

No restrictions. This document is available through the National Technical Information Service,
Springfield, VA 22161.
http://www.ntis.gov

19. Security Classification
(of this report)

Unclassified

20. Security Classification
(of this page)

Unclassified

21. No. of Pages

123

22. Price
Form DOT F 1700.7 (8-72) Reproduction of completed page authorized

SI* (Modern Metric) Conversion Factors

TABLE OF CONTENTS

CHAPTER 1. BACKGROUND AND OBJECTIVES

CHAPTER 2. LITERATURE REVIEW

CHAPTER 3. CONCEPTUAL MODEL FOR FLUSH RIPRAP APRONS

CHAPTER 4. PHYSICAL MODELING

CHAPTER 5. NUMERICAL MODELING

CHAPTER 6. RECOMMENDED DESIGN GUIDANCE

CHAPTER 7. SUMMARY AND FUTURE RESEARCH

APPENDIX A. ANNOTATED LITERATURE REVIEW

APPENDIX B. EQUILIBRIUM SCOUR MAPS FROM THE PHYSICAL EXPERIMENTS

APPENDIX C. CFD SHEAR STRESS AND VELOCITY DISTRIBUTIONS

APPENDIX D. HYDRAULIC REQUIREMENTS FOR SHALLOW ABUTMENT FOUNDATIONS

REFERENCES

LIST OF FIGURES



LIST OF TABLES

LIST OF ABBREVIATIONS AND SYMBOLS

Abbreviations

ADVacoustic Doppler velocimeter 
CFDcomputational fluid dynamics 
CTBcable-tied block 
DGDesign Guideline 
FHWAFederal Highway Administration 
GRSgeosynthetic reinforced soil 
HECHydraulic Engineering Circular  
IBSIntegrated Bridge System 
LTDlong-term degradation 
NCHRPNational Cooperative Highway Research Program 
PIVparticle image velocimetry 
RSFreinforced soil foundation 
TFHRCTurner-Fairbank Highway Research Center 
V:Hvertical-to-horizontal 

Symbols

A0cross-sectional area of contracted section before contraction scour (ft2 (m2))  
A1cross-sectional area of upstream section (ft2 (m2))  
Â1cross-sectional area of upstream section for computational fluid dynamics experiments (ft2 (m2))  
A2cross-sectional area of contracted section without riprap at equilibrium contraction scour (ft2 (m2)) 
A2Rcross-sectional area of contracted section with riprap after contraction scour to a depth of yc (ft2 (m2)) 
A2bcross-sectional area of contracted section before contraction scour (ft2 (m2)) 
α1energy correction factor for upstream section (dimensionless) 
α2Benergy correction factor for contracted section without riprap (dimensionless) 
α2eenergy correction factor for equivalent contracted section with riprap (dimensionless) 
α2Renergy correction factor for contracted section with riprap (dimensionless) 
βBchannel shape factor for model without riprap (dimensionless) 
βechannel shape factor for equivalent model with riprap (dimensionless) 
βRchannel shape factor for model with riprap (dimensionless) 
CcBcontraction coefficient for model without riprap (dimensionless) 
Ccecontraction coefficient for equivalent model with riprap (dimensionless) 
CcRcontraction coefficient for model with riprap (dimensionless) 
D50median noncohesive material size (bed material or riprap) (ft (m))  
Δ Zvertical adjustment for equivalent depth (ft (m)) 
εfunction related to ratio of roughness coefficient of riprap to that of erodible bed material (dimensionless) 
FrFroude number (dimensionless) 
Froud numberFroude number for CFD experiments (dimensionless) 
gacceleration from gravity (ft/s2 (m/s2)) 
γunit weight of water (lbf/ft3 (N/m3)) 
hBhead loss between upstream section and contracted section without riprap (ft (m)) 
hehead loss between upstream section and equivalent contracted section with riprap (ft(m)) 
hRhead loss between upstream section and contracted section with riprap (ft (m)) 
Krcoefficient equals to 0.89 for a spill-through abutment and 1.02 for vertical-wall abutment (dimensionless) 
l1abutment length (ft (m)) 
l2abutment width (ft (m)) 
μviscosity (lbf∙s/ft2 (N∙s/m2)) 
ncomposite Manning’s roughness coefficient (dimensionless) 
nBroughness coefficient for bed material (dimensionless) 
nRroughness coefficient for riprap (dimensionless) 
undefined function 
Pddownstream flow pressure (lbf/ft2 (N/m2)) 
Puupstream flow pressure (lbf/ft2 (N/m2)) 
Qdischarge (ft3/s (m3/s)) 
ReReynolds number (dimensionless) 
ρwater density (lb/ft3 (kg/m3)) 
Rhhydraulic radius (ft (m)) 
Senergy slope in contracted section (ft/ft (m/m))  
Sgspecific gravity of rock riprap (dimensionless) 
τashear on front face of abutment (lbf/ft2 (N/m2 or Pa)) 
τavgaverage bed shear stress for model with riprap (lbf/ft2 (N/m2 or Pa)) 
τBaverage bed shear stress in middle portion of contracted section without riprap with scour at a depth of yc (lbf/ft2 (N/m2 or Pa)) 
τccritical shear stress on bed for model without riprap (lbf/ft2 (N/m2 or Pa)) 
τoaverage bed shear stress in contracted section without riprap before scour (lbf/ft2 (N/m2 or Pa)) 
τRaverage bed shear stress in contracted section between riprap aprons with scour at a depth of yc (lbf/ft2 (N/m2 or Pa)) 
τripaverage bed shear stress on riprap (lbf/ft2 (N/m2 or Pa)) 
V0average velocity in contracted section before contraction scour (ft/s (m/s)) 
V1average velocity in upstream section (ft/s (m/s)) 
velosity1average velocity in upstream section for CFD experiments (ft/s (m/s))  
V2average velocity in contracted section without riprap at equilibrium contraction scour (ft/s (m/s)) 
V2baverage velocity in contracted section before contraction scour (ft/s (m/s)) 
V2Raverage velocity in contracted section with riprap after contraction scour to a depth of the average equilibrium scour without riprap (yc) (ft/s (m/s)) 
W1bottom width of upstream section (ft (m)) 
W1Ttop width of upstream section (ft (m)) 
width1average width in upstream section (ft (m)) 
W2bottom width of contracted section (bridge opening width) (ft (m)) 
WBbottom width of bed material (ft (m))  
WR riprap apron width (ft (m)) 
y1average flow depth in upstream section (ft (m)) 
y1Mmaximum flow depth in upstream section (ft (m)) 
ŷ1average flow depth in upstream section for CFD experiments (ft (m))  
y2average flow depth in contracted section with riprap after contraction scour (ft (m)) 
y2Mmaximum flow depth in contracted section with riprap after contraction scour (ft (m)) 
y2Raverage flow depth in contracted section with riprap at equilibrium contraction scour (ft (m)) 
y2RMmaximum flow depth in contracted section with riprap at equilibrium contraction scour (ft (m)) 
yc average equilibrium contraction scour depth without riprap (ft (m)) 
ycR maximum contraction scour depth with partial-width riprap scour countermeasures (ft(m)) 
yeequivalent flow depth in contracted section (ft (m)) 
y0average flow depth in contracted section before contraction scour (ft (m)) 
y0Mmaximum flow depth in contracted section before contraction scour (ft (m)) 
yslocal scour depth (ft (m)) 
z1reference elevation for upstream section (ft (m)) 
z2reference elevation for downstream section (ft (m)) 

 

 

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