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.

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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

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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

AASHTO	American Association of State Highway and Transportation Officials
COTR	Contracting Officer's Technical Representative
DOT	Department of Transportation
FHWA	Federal Highway Administration
MSE	Mean Square Error
NTIS	National Technical Information Service
RSQ	Correlation Coefficient
R2	Correlation Coefficient
SG	Specific Gravity
SHA	State Highway Administration
SI	International System of Units (metric system)
SMB	Shields, Manning, and Blodgett
TFHRC	Turner-Fairbank Highway Research Center
VC	Critical Velocity
VI	Virtual Instruments
VR	Representative Velocity
W.S.	Water Surface

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Page Owner: Office of Research, Development, and Technology, Office of Infrastructure, RDT Scheduled Update: Archive - No Update Technical Issues: TFHRC.WebMaster@dot.gov Topics: research, infrastructure, hydraulics Keywords: research, infrastructure, hydraulics, Scour, culverts, hydraulics, physical model TRT Terms: research, hydraulics, hydrology, fluid mechanics, earth sciences, geophysics Updated: 04/23/2012