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Publication Number: FHWA-RD-02-078
Date: November 2003

Bottomless Culvert Scour Study: Phase I Laboratory Report

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FOREWORD

The bottomless culvert study described in this report was conducted at the Federal Highway Administration (FHWA) hydraulics laboratory in response to a request by the Maryland State Highway Administration (SHA) in a partnership arrangement in which the Maryland SHA shared the cost of the study. Two suppliers, CONTECH® and CONSPAN®, agreed to provide models of the typical configurations that are used for highway applications. Part of the study objective was to compare results from a simple rectangular shape to the results from shapes that are typically available from the suppliers. This report presents the results of laboratory experiments; it does not represent FHWA policy or endorsement of design concepts. This report is being distributed as an electronic document through the Turner- Fairbank Highway Research Center web Web site (www.tfhrc.gov).

T. Paul Teng, P.E.
Director, Office of Infrastructure
Research and Development

 

NOTICE

This document is disseminated under the sponsorship of the U.S. Department of OTransportation in the interest of information exchange. The United StatesU.S. Government assumes no liability for its contents or use thereof. This report does not constitute a standard, specification, policy, or regulation.

The U.S. Government does not endorse products or manufacturers. Trade and manufacturers' names appear in this report only because they are considered essential to the object of the document.


Technical Report Documentation Page

1. Report No.
FHWA-RD-02-078
2. Government Accession No.3. Recipient's Catalog No.
4. Title and Subtitle
BOTTOMLESS CULVERT SCOUR STUDY: PHASE I LABORATORY REPORT
5. Report Date
6. Performing Organization Code
VTRC 02-R
7. Author(s)
Kornel Kerenyi, J. Sterling Jones, and Stuart Stein
8. Performing Organization Report No.
9. Performing Organization Name and Address
GKY and Associates, Inc.
5411-E Backlick Road
Springfield, VA 22151
10. Work Unit No. (TRAIS)
11. Contract or Grant No.
DTFH61-95-C-00066
12. Sponsoring Agency Name and Address
Office of Infrastructure Research and Development
Federal Highway Administration
6300 Georgetown Pike
McLean, Virginia 22102-2296
13. Type of Report and Period Covered
Laboratory Report
March 2000-December 2000
14. Sponsoring Agency Code
15. Supplementary Notes
Contracting Officer's Technical Representative (COTR): J. Sterling Jones, HRDI-07The Maryland State Highway Administration (SHA) provided technical assistance and partial funding for this study. Dr. Fred Chang was instrumental in setting up the experimental plan and provided a data analysis strategy. Dr. Xibing Dou provided numerical model results.
16. Abstract
Bottomless culverts are three-sided structures that have sides and a top and use the natural channel for the bottom. As such, they are an environmentally attractive alternative to box, pipe, and pipe arch culvert designs. Bottomless culverts range in size from a few feet to more than 10 meters (35 feet) in width. The failure of such a structure could have severe consequences similar to the failure of a bridge. On the other hand, since the cost of the foundation and scour countermeasures represent a significant portion of the cost of the structure, overdesign of these elements can add significantly to the cost of the project. The Maryland SHA funded a study of scour at bottomless culverts. Several dozen physical modeling configurations were tested and the resulting scour was measured. The results were evaluated and predictive equations for estimating scour depth were developed. These equations will provide guidance for the design of footing depths for bottomless culverts. Additional tests were conducted to determine the riprap sizes needed to prevent the deep scour that was observed near the upstream corners of the culvert when there was substantial approach flow blocked by the roadway embankments. These tests were preliminary and are not an indication that the Federal Highway Administration endorses the concept of using a countermeasure to reduce foundation depth.
17. Key Words
Scour, culverts, hydraulics, physical model.
18. Distribution Statement
No restrictions. This document is available to the public through the National Technical Information Service (NTIS), Springfield, VA 22161.
19. Security Classif. (of this report)
Unclassified
20. Security Classif. (of this page)
Unclassified
21. No. of Pages
69
22. Price

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


SI* (Modern Metric) Conversion Factors

Table of Contents
LIST OF TABLES
LIST OF FIGURES
LIST OF ACRONYMS AND ABBREVIATIONS

  1. INTRODUCTION
  2. EXPERIMENTAL APPROACH
    TEST FACILITIES AND INSTRUMENTATION
       Hydraulic Flume
       Electromagnetic Velocity Meter Operation
       Post-Processing and Data Analysis
    MODEL BOTTOMLESS CULVERT SHAPES
    EXPERIMENTAL PARAMETERS
  3. THEORETICAL BACKGROUND
    CALCULATING REPRESENTATIVE VELOCITY
       Maryland DOT (Chang) Method for Representative Velocity
       GKY Method for Representative Velocity
    NUMERICAL MODEL FOR CALCULATING REPRESENTATIVE VELOCITY
    CALCULATING CRITICAL VELOCITY
       Maryland DOT (Chang) Method for Critical Velocity
         Niell's Competent Velocity Concept
       GKY Method for Critical Velocity
         Combined Competent Velocity Curves
    SCOUR PROTECTION TASK: RIPRAP ANALYSIS
  4. RESULTS
    SCOUR RESULTS
       Maryland DOT (Chang) Method for Representative Velocity and Critical Velocity
       GKY Method for Representative Velocity and Maryland DOT (Chang) Method for Critical Velocity
       GKY Method for Representative Velocity and Critical Velocity
    RIPRAP RESULTS
       Maryland DOT (Chang) Method for Representative Velocity
       GKY Method for Representative Velocity
  5. CONCLUSIONS
  6. RECOMMENDED PROCEDURES FOR ESTIMATING MAXIMUM SCOUR FOR BOTTOMLESS CULVERTS
    PROCEDURE USING GKY METHOD FOR REPRESENTATIVE VELOCITY AND SMB EQUATION FOR CRITICAL VELOCITY
    PROCEDURE USING MARYLAND DOT (CHANG) METHOD FOR REPRESENTATIVE VELOCITY AND CRITICAL VELOCITY
  7. REFERENCES

LIST OF FIGURES

  1. View of the flume in the Hydraulics Laboratory
  2. Example of a front panel
  3. Example of a block diagram
  4. Rectangular model, vertical face
  5. Rectangular model with wingwalls
  6. CONSPAN model
  7. CONSPAN model with wingwalls
  8. CONTECH model
  9. Rectangular model from the scour protection task
  10. Flow concentration and separation zone
  11. (a). Definition sketch prior to scour
    (b). Definition sketch after scour
    c). Definition sketch for blocked area
  12. Chang's resultant velocity location
  13. GKY's resultant velocity approach
  14. Velocity locations for 2D model
  15. Resultant velocity comparison with numerical model at location 2
  16. Comparison of Chang's and GKY's resultant velocities
  17. Competent velocity curves for the design of waterway openings in scour backwater conditions (from Niell)
  18. Chang's approximations
  19. Shields parameter as a function of the particle Reynolds number
  20. Combined competent velocity curves for a flow depth of 3 m (10 ft)
  21. Combined competent velocity curves for a flow depth of 0.3 m (1.0 ft)
  22. Post-processing: Data analysis flow chart
  23. Maryland DOT's (Chang's) resultant velocity with Chang's approximation equation and local scour ratio as a function of the Froude number, using a linear regression
  24. Measured and computed data with and without wingwalls
  25. Maryland DOT's (Chang's) resultant velocity with Chang's approximation equation for critical velocity and local scour ratio as a function of the Froude number, using a second order regression
  26. Measured and computed data with and without wingwalls
  27. Maryland DOT's (Chang's) resultant velocity with Chang's approximation for critical velocity and local scour ratio as a function of the Froude number, using a linear regression
  28. Measured and computed data with and without wingwalls
  29. Maryland DOT's (Chang's) resultant velocity with Chang's approximation for critical velocity and local scour ratio as a function of the blocked area over the squared flow depth
  30. Measured and computed data with and without wingwalls
  31. Maryland DOT's (Chang's) resultant velocity with Chang's approximation for critical velocity and local scour ratio as a function of the blocked area over the squared computed equilibrium depth
  32. Measured and computed data with and without wingwalls
  33. Maryland DOT's (Chang's) resultant velocity with Chang's approximation equation and local scour ratio as a function of the blocked discharge normalized by the acceleration of gravity (g) and the computed equilibrium depth
  34. Measured and computed data with and without wingwalls
  35. GKY's resultant velocity with Chang's approximation equation for critical velocity and local scour ratio as a function of the blocked area over the squared flow depth
  36. Measured and computed data with and without wingwalls
  37. GKY's resultant velocity with Chang's approximation equation for critical velocity and local scour ratio as a function of the blocked area over the squared computed equilibrium depth
  38. Measured and computed data with and without wingwalls
  39. GKY's resultant velocity with the SMB equation for critical velocity and local scour ratio as a function of the blocked area over the squared flow depth
  40. Measured and computed data with and without wingwalls
  41. GKY's resultant velocity with the SMB equation for critical velocity and local scour ratio as a function of the blocked area over the squared computed equilibrium depth
  42. Measured and computed data with and without wingwalls
  43. GKY's resultant velocity with the SMB equation for critical velocity and local scour ratio as a function of the blocked discharge normalized by the acceleration of gravity (g) and the computed equilibrium depth
  44. Measured and computed data with and without wingwalls
  45. Maryland DOT's (Chang's) resultant velocity and stable riprap size from the Ishbash equation with the blocked area over the squared flow depth as the independent regression variable
  46. Measured and computed data
  47. Maryland DOT's (Chang's) resultant velocity and stable riprap size from the Ishbash equation with the blocked discharge normalized by the acceleration of gravity (g) and the flow depth as the independent regression variable
  48. Measured and computed data
  49. GKY''s resultant velocity and stable riprap size from the Ishbash equation with the blocked area over the squared flow depth as the independent regression variable
  50. Measured and computed data
  51. GKY's resultant velocity and stable riprap size from the Ishbash equation with the blocked discharge normalized by the acceleration of gravity (g) and the flow depth as the independent regression variable
  52. Measured and computed data

LIST OF TABLES

  1. Independent regression variables and R2 values using the Maryland DOT (Chang) method
  2. Independent regression variables and R2 values using the GKY and Maryland DOT (Chang) methods
  3. Independent regression variables and R2 values using the GKY method for representative velocity and critical velocity
  4. Independent regression variables and R2 values using the Maryland DOT (Chang) method for representative velocity
  5. Independent regression variables and R2 values using the GKY method for representative velocity

LIST OF ACRONYMS AND ABBREVIATIONS
AASHTOAmerican Association of State Highway and Transportation Officials
COTRContracting Officer's Technical Representative
DOT Department of Transportation
FHWA Federal Highway Administration
MSEMean Square Error
NTISNational Technical Information Service
RSQ Correlation Coefficient
R2Correlation Coefficient
SG Specific Gravity
SHA State Highway Administration
SIInternational System of Units (metric system)
SMB Shields, Manning, and Blodgett
TFHRC Turner-Fairbank Highway Research Center
VCCritical Velocity
VI Virtual Instruments
VRRepresentative Velocity
W.S. Water Surface

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The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT).
The Federal Highway Administration (FHWA) is a part of the U.S. Department of Transportation and is headquartered in Washington, D.C., with field offices across the United States. is a major agency of the U.S. Department of Transportation (DOT). The hydraulics and hydrology research program at the TFHRC Federal Highway Administration's (FHWA) R&T Web site portal, which provides access to or information about the Agency’s R&T program, projects, partnerships, publications, and results.
FHWA
United States Department of Transportation - Federal Highway Administration