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NATIONAL NCHRP REPORT 516 COOPERATIVE HIGHWAY RESEARCH PROGRAM Pier and Contraction Scour in Cohesive Soils

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TRANSPORTATION RESEARCH BOARD EXECUTIVE COMMITTEE 2004 (Membership as of July 2004) OFFICERS Chair: Michael S. Townes, President and CEO, Hampton Roads Transit, Hampton, VA Vice Chair: Joseph H. Boardman, Commissioner, New York State DOT Executive Director: Robert E. Skinner, Jr., Transportation Research Board MEMBERS MICHAEL W. BEHRENS, Executive Director, Texas DOT SARAH C. CAMPBELL, President, TransManagement, Inc., Washington, DC E. DEAN CARLSON, Director, Carlson Associates, Topeka, KS JOHN L. CRAIG, Director, Nebraska Department of Roads DOUGLAS G. DUNCAN, President and CEO, FedEx Freight, Memphis, TN GENEVIEVE GIULIANO, Director, Metrans Transportation Center and Professor, School of Policy, Planning, and Development, USC, Los Angeles BERNARD S. GROSECLOSE, JR., President and CEO, South Carolina State Ports Authority SUSAN HANSON, Landry University Professor of Geography, Graduate School of Geography, Clark University JAMES R. HERTWIG, President, CSX Intermodal, Jacksonville, FL GLORIA J. JEFF, Director, Michigan DOT ADIB K. KANAFANI, Cahill Professor of Civil Engineering, University of California, Berkeley RONALD F. KIRBY, Director of Transportation Planning, Metropolitan Washington Council of Governments HERBERT S. LEVINSON, Principal, Herbert S. Levinson Transportation Consultant, New Haven, CT SUE MCNEIL, Director, Urban Transportation Center and Professor, College of Urban Planning and Public Affairs and Department of Civil and Material Engineering, University of Illinois, Chicago MICHAEL D. MEYER, Professor, School of Civil and Environmental Engineering, Georgia Institute of Technology CAROL A. MURRAY, Commissioner, New Hampshire DOT JOHN E. NJORD, Executive Director, Utah DOT DAVID PLAVIN, President, Airports Council International, Washington, DC JOHN H. REBENSDORF, Vice President, Network Planning and Operations, Union Pacific Railroad Co., Omaha, NE PHILIP A. SHUCET, Commissioner, Virginia DOT C. MICHAEL WALTON, Ernest H. Cockrell Centennial Chair in Engineering, University of Texas, Austin LINDA S. WATSON, Executive Director, LYNX--Central Florida Regional Transportation Authority, Orlando, FL MARION C. BLAKEY, Federal Aviation Administrator, U.S.DOT (ex officio) SAMUEL G. BONASSO, Acting Administrator, Research and Special Programs Administration, U.S.DOT (ex officio) REBECCA M. BREWSTER, President and COO, American Transportation Research Institute, Smyrna, GA (ex officio) GEORGE BUGLIARELLO, Chancellor, Polytechnic University and Foreign Secretary, National Academy of Engineering (ex officio) THOMAS H. COLLINS (Adm., U.S. Coast Guard), Commandant, U.S. Coast Guard (ex officio) JENNIFER L. DORN, Federal Transit Administrator, U.S.DOT (ex officio) EDWARD R. HAMBERGER, President and CEO, Association of American Railroads (ex officio) JOHN C. HORSLEY, Executive Director, American Association of State Highway and Transportation Officials (ex officio) RICK KOWALEWSKI, Deputy Director, Bureau of Transportation Statistics, U.S.DOT (ex officio) WILLIAM W. MILLAR, President, American Public Transportation Association (ex officio) BETTY MONRO, Acting Administrator, Federal Railroad Administration, U.S.DOT (ex officio) MARY E. PETERS, Federal Highway Administrator, U.S.DOT (ex officio) SUZANNE RUDZINSKI, Director, Transportation and Regional Programs, U.S. Environmental Protection Agency (ex officio) JEFFREY W. RUNGE, National Highway Traffic Safety Administrator, U.S.DOT (ex officio) ANNETTE M. SANDBERG, Federal Motor Carrier Safety Administrator, U.S.DOT (ex officio) WILLIAM G. SCHUBERT, Maritime Administrator, U.S.DOT (ex officio) JEFFREY N. SHANE, Under Secretary for Policy, U.S.DOT (ex officio) CARL A. STROCK (Maj. Gen., U.S. Army), Chief of Engineers and Commanding General, U.S. Army Corps of Engineers (ex officio) ROBERT A. VENEZIA, Program Manager of Public Health Applications, National Aeronautics and Space Administration (ex officio) NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Transportation Research Board Executive Committee Subcommittee for NCHRP MICHAEL S. TOWNES, Hampton Roads Transit, Hampton, VA JOHN C. HORSLEY, American Association of State Highway (Chair) and Transportation Officials JOSEPH H. BOARDMAN, New York State DOT MARY E. PETERS, Federal Highway Administration GENEVIEVE GIULIANO, University of Southern California, ROBERT E. SKINNER, JR., Transportation Research Board Los Angeles C. MICHAEL WALTON, University of Texas, Austin

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NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM NCHRP REPORT 516 Pier and Contraction Scour in Cohesive Soils J.-L. BRIAUD H.-C. CHEN Y. LI P. NURTJAHYO AND J. WANG Texas A&M University College Station, TX S UBJECT A REAS Highway and Facility Design Bridges, Other Structures, and Hydraulics and Hydrology Soils, Geology, and Foundations Materials and Construction Research Sponsored by the American Association of State Highway and Transportation Officials in Cooperation with the Federal Highway Administration TRANSPORTATION RESEARCH BOARD WASHINGTON, D.C. 2004 www.TRB.org

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NATIONAL COOPERATIVE HIGHWAY RESEARCH NCHRP REPORT 516 PROGRAM Systematic, well-designed research provides the most effective Project E24-15 FY'98 approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local ISSN 0077-5614 interest and can best be studied by highway departments ISBN 0-309-088062 individually or in cooperation with their state universities and Library of Congress Control Number 2004096313 others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to 2004 Transportation Research Board highway authorities. These problems are best studied through a coordinated program of cooperative research. Price $22.00 In recognition of these needs, the highway administrators of the American Association of State Highway and Transportation Officials initiated in 1962 an objective national highway research program employing modern scientific techniques. This program is supported on a continuing basis by funds from participating member states of the Association and it receives the full cooperation and support of the Federal Highway Administration, United States NOTICE Department of Transportation. The project that is the subject of this report was a part of the National Cooperative The Transportation Research Board of the National Academies Highway Research Program conducted by the Transportation Research Board with the was requested by the Association to administer the research approval of the Governing Board of the National Research Council. Such approval program because of the Board's recognized objectivity and reflects the Governing Board's judgment that the program concerned is of national understanding of modern research practices. The Board is uniquely importance and appropriate with respect to both the purposes and resources of the suited for this purpose as it maintains an extensive committee National Research Council. structure from which authorities on any highway transportation The members of the technical committee selected to monitor this project and to review subject may be drawn; it possesses avenues of communications and this report were chosen for recognized scholarly competence and with due cooperation with federal, state and local governmental agencies, consideration for the balance of disciplines appropriate to the project. The opinions and universities, and industry; its relationship to the National Research conclusions expressed or implied are those of the research agency that performed the Council is an insurance of objectivity; it maintains a full-time research, and, while they have been accepted as appropriate by the technical committee, research correlation staff of specialists in highway transportation they are not necessarily those of the Transportation Research Board, the National matters to bring the findings of research directly to those who are in Research Council, the American Association of State Highway and Transportation a position to use them. Officials, or the Federal Highway Administration, U.S. Department of Transportation. The program is developed on the basis of research needs Each report is reviewed and accepted for publication by the technical committee identified by chief administrators of the highway and transportation according to procedures established and monitored by the Transportation Research departments and by committees of AASHTO. Each year, specific Board Executive Committee and the Governing Board of the National Research areas of research needs to be included in the program are proposed Council. to the National Research Council and the Board by the American Association of State Highway and Transportation Officials. Research projects to fulfill these needs are defined by the Board, and qualified research agencies are selected from those that have submitted proposals. Administration and surveillance of research contracts are the responsibilities of the National Research Council and the Transportation Research Board. Published reports of the The needs for highway research are many, and the National NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of are available from: mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or Transportation Research Board duplicate other highway research programs. Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: Note: The Transportation Research Board of the National Academies, the National Research Council, the Federal Highway Administration, the American Association of State Highway and Transportation Officials, and the individual http://www.national-academies.org/trb/bookstore states participating in the National Cooperative Highway Research Program do not endorse products or manufacturers. Trade or manufacturers' names appear herein solely because they are considered essential to the object of this report. Printed in the United States of America

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The National Academy of Sciences is a private, nonprofit, self-perpetuating society of distinguished schol- ars engaged in scientific and engineering research, dedicated to the furtherance of science and technology and to their use for the general welfare. On the authority of the charter granted to it by the Congress in 1863, the Academy has a mandate that requires it to advise the federal government on scientific and techni- cal matters. Dr. Bruce M. Alberts is president of the National Academy of Sciences. The National Academy of Engineering was established in 1964, under the charter of the National Acad- emy of Sciences, as a parallel organization of outstanding engineers. It is autonomous in its administration and in the selection of its members, sharing with the National Academy of Sciences the responsibility for advising the federal government. The National Academy of Engineering also sponsors engineering programs aimed at meeting national needs, encourages education and research, and recognizes the superior achieve- ments of engineers. Dr. William A. Wulf is president of the National Academy of Engineering. The Institute of Medicine was established in 1970 by the National Academy of Sciences to secure the services of eminent members of appropriate professions in the examination of policy matters pertaining to the health of the public. The Institute acts under the responsibility given to the National Academy of Sciences by its congressional charter to be an adviser to the federal government and, on its own initiative, to identify issues of medical care, research, and education. Dr. Harvey V. Fineberg is president of the Institute of Medicine. The National Research Council was organized by the National Academy of Sciences in 1916 to associate the broad community of science and technology with the Academy's purposes of furthering knowledge and advising the federal government. Functioning in accordance with general policies determined by the Acad- emy, the Council has become the principal operating agency of both the National Academy of Sciences and the National Academy of Engineering in providing services to the government, the public, and the scientific and engineering communities. The Council is administered jointly by both the Academies and the Institute of Medicine. Dr. Bruce M. Alberts and Dr. William A. Wulf are chair and vice chair, respectively, of the National Research Council. The Transportation Research Board is a division of the National Research Council, which serves the National Academy of Sciences and the National Academy of Engineering. The Board's mission is to promote innovation and progress in transportation through research. In an objective and interdisciplinary setting, the Board facilitates the sharing of information on transportation practice and policy by researchers and practitioners; stimulates research and offers research management services that promote technical excellence; provides expert advice on transportation policy and programs; and disseminates research results broadly and encourages their implementation. The Board's varied activities annually engage more than 5,000 engineers, scientists, and other transportation researchers and practitioners from the public and private sectors and academia, all of whom contribute their expertise in the public interest. The program is supported by state transportation departments, federal agencies including the component administrations of the U.S. Department of Transportation, and other organizations and individuals interested in the development of transportation. www.TRB.org www.national-academies.org

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COOPERATIVE RESEARCH PROGRAMS STAFF FOR NCHRP REPORT 516 ROBERT J. REILLY, Director, Cooperative Research Programs CRAWFORD F. JENCKS, Manager, NCHRP TIMOTHY G. HESS, Senior Program Officer EILEEN P. DELANEY, Director of Publications HILARY FREER, Editor NCHRP PROJECT E24-15 PANEL Field of Soils and Geology--Area of Mechanics and Foundations STEVEN P. SMITH, PBS&J-Denver, Greenwood Village, CO (Chair) LARRY A. ARNESON, FHWA DARYL J. GREER, Kentucky Transportation Cabinet ROBERT W. HENTHORNE, Kansas DOT MELINDA LUNA, Lower Colorado River Authority WILLIAM L. MOORE, North Carolina DOT RICHARD A. PHILLIPS, South Dakota DOT MEHMET T. TUMAY, Louisiana State University J. STERLING JONES, FHWA Liaison Representative G. P. JAYAPRAKASH, TRB Liaison Representative AUTHOR ACKNOWLEDGMENTS Special thanks go to the NCHRP group associated with this proj- We also wish to acknowledge the help from people at Texas ect for their advice and comments throughout the study: the A&M University, including John Reed, Bob Randall, Andrew Faw- NCHRP Project Panel and NCHRP staff. cett, Mike Linger, Richard Gehle, and Josh Reinbolt. Special thanks also go to our consultants: Peter Lagasse, Ayres Associates; Peter Smith, Parsons Brinckerhoff Quade & Douglas, Inc.; and Art Parola, Jr., University of Louisville.

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This report discusses the findings of a research project undertaken to investigate FOREWORD bridge scour in cohesive soils. The report presents a recommended method for pre- By Timothy G. Hess dicting the extent of complex pier and contraction scour in cohesive soils. This report Staff Officer will be of immediate interest to engineers with responsibility for predicting the extent Transportation Research of scour at bridge foundations and to engineers with responsibility for designing bridge Board foundations and bridge scour countermeasures. Scour at bridges founded in or on cohesive soil is a complex phenomenon that is not completely understood. Conventional approaches to scour prediction were devel- oped from laboratory experiments in cohesionless materials and are generally regarded as overly conservative when applied to cohesive soils. Accurate and accepted methods for predicting scour depths in cohesive soils that account for the soil's greater scour resistance are not yet available to practicing engineers. The lack of an accurate predic- tive method often results in an overly conservative and sometimes unnecessarily costly bridge foundation. Research investigating the relationship between properties of cohe- sive material and the erosive power of flowing water is needed to improve the predic- tion of scour in cohesive soils. Under NCHRP Project 24-15, the Texas Transportation Institute developed a method for predicting pier and contraction scour in cohesive soil. The research team first reviewed the literature to identify existing knowledge in the subject area. The design of an erosion function apparatus (EFA) developed in earlier research was enhanced, and a new EFA was constructed and used in the development of erosion curves for specific soils. Laboratory flume tests were conducted, followed by numeri- cal simulations; and finally prediction equations were developed. The prediction method developed, termed SRICOS (Scour Rate In Cohesive Soils), was applied to several contraction and complex-pier configurations typically encountered by state highway agencies. An evaluation of the accuracy and precision of the SRICOS Method was conducted by comparing predicted and measured data. Exam- ple problems using the SRICOS Method were developed to assist practitioners in applying the method. A computer program, termed SRICOS-EFA was developed to automate the calculations used in the SRICOS Method and to assist in the imple- mentation of the research results. NCHRP Report 516 includes a discussion of existing knowledge and practice, a description of the erosion function apparatus, a discussion of laboratory tests and numer- ical simulations conducted, presentation of the SRICOS-EFA method, and one appen- dix, Appendix A: Photographs from the Flume Tests. Compilations of flume test data and case history data were provided by the Texas Transportation Institute but are not included in this publication; however, they are available on request from NCHRP. Sub- sequent to completion of NCHRP Project 24-15, the Texas Transportation Institute updated the SRICOS-EFA computer program and added other enhancements. The SRICOS-EFA computer program and User's Manual are available from the Texas Transportation Institute via the internet at http://ceprofs.tamu.edu/briaud/sricos-efa.htm.

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CONTENTS 1 SUMMARY 8 CHAPTER 1 Introduction 1.1 Bridge Scour, 8 1.2 Classification of Soils, 8 1.3 The Problem Addressed, 8 1.4 Why Was This Problem Addressed?, 8 1.5 Approach Selected to Solve the Problem, 9 10 CHAPTER 2 Erodibility of Cohesive Soils 2.1 Erodibility: A Definition, 10 2.2 Erosion Process, 10 2.3 Existing Knowledge on Erodibility of Cohesive Soils, 10 2.4 Erodibility and Correlation to Soil and Rock Properties, 10 14 CHAPTER 3 Erosion Function Apparatus (EFA) 3.1 Concept, 14 3.2 EFA Test Procedure, 14 3.3 EFA Test Data Reduction, 14 3.4 EFA Precision and Typical Results, 15 17 CHAPTER 4 The SRICOS-EFA Method for Cylindrical Piers in Deep Water 4.1 SRICOS-EFA Method for Constant Velocity and Uniform Soil, 17 4.2 Small Flood Followed by Big Flood, 17 4.3 Big Flood Followed by Small Flood and General Case, 18 4.4 Hard Soil Layer Over Soft Soil Layer, 19 4.5 Soft Soil Layer Over Hard Soil Layer and General Case, 21 4.6 Equivalent Time, 21 4.7 Extended and Simple SRICOS-EFA Method, 22 4.8 Case Histories, 24 4.9 Predicted and Measured Local Scour for the Eight Bridges, 26 4.10 Conclusions, 29 30 CHAPTER 5 The SRICOS-EFA Method for Maximum Scour Depth at Complex Piers 5.1 Existing Knowledge, 30 5.2 General, 30 5.3 Flumes and Scour Models, 30 5.4 Measuring Equipment, 30 5.5 Soils and Soil Bed Preparation, 32 5.6 Flume Tests: Procedure and Measurement, 33 5.7 Shallow Water Effect: Flume Test Results, 34 5.8 Shallow Water Effect on Maximum Pier Scour Depth, 34 5.9 Shallow Water Effect on Initial Shear Stress, 36 5.10 Pier Spacing Effect: Flume Test Results, 37 5.11 Pier Spacing Effect on Maximum Scour Depth, 37 5.12 Pier Spacing Effect on Initial Scour Rate, 38 5.13 Pier Shape Effect: Flume Test Results, 39 5.14 Pier Shape Effect on Maximum Scour Depth, 39 5.15 Pier Shape Effect on Initial Scour Rate, 39 5.16 Pier Shape Effect on Pier Hole Shapes, 40 5.17 Attack Angle Effect: Flume Test Results, 40 5.18 Attack Angle Effect on Maximum Scour Depth, 40 5.19 Attack Angle Effect on Initial Scour Rate, 42 5.20 Attack Angle Effect on Scour Hole Shape, 42 5.21 Maximum Scour Depth Equation for Complex Pier Scour, 43 45 CHAPTER 6 The SRICOS-EFA Method for Initial Scour Rate at Complex Piers 6.1 General, 45 6.2 Existing Knowledge on Numerical Simulations for Scour, 45 6.3 Numerical Method Used in This Study, 46 6.4 Verification of the Numerical Method, 46 6.5 Shallow Water Effect: Numerical Simulation Results, 46 6.6 Shallow Water Effect on Maximum Shear Stress, 47

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6.7 Pier Spacing Effect: Numerical Simulation Results, 48 6.8 Pier Spacing Effect on Maximum Shear Stress, 49 6.9 Pier Shape Effect: Numerical Simulation Results, 49 6.10 Pier Shape Effect on Maximum Shear Stress, 51 6.11 Attack Angle Effect: Numerical Simulation Results, 52 6.12 Attack Angle Effect on Maximum Shear Stress, 53 6.13 Maximum Shear Stress Equation for Complex Pier Scour, 54 56 CHAPTER 7 The SRICOS-EFA Method for Maximum Contraction Scour Depth 7.1 Existing Knowledge, 56 7.2 General, 56 7.3 Flume Tests and Measurements, 56 7.4 Flume Tests: Flow Observations and Results, 57 7.5 Flume Tests: Scour Observations and Results, 59 7.6 Maximum and Uniform Contraction Depths for the Reference Cases, 60 7.7 Location of Maximum Contraction Depth for the Reference Cases, 63 7.8 Correction Factors for Transition Angle and Contraction Length, 64 7.9 SRICOS-EFA Method Using HEC-RAS Generated Velocity, 65 7.10 Constructing the Complete Contraction Scour Profile, 66 7.11 Scour Depth Equations for Contraction Scour, 66 68 CHAPTER 8 The SRICOS-EFA Method for Initial Scour Rate at Contracted Channels 8.1 Background, 68 8.2 Contraction Ratio Effect: Numerical Simulation Results, 68 8.3 Transition Angle Effect: Numerical Simulation Results, 68 8.4 Contracted Length Effect: Numerical Simulation Results, 69 8.5 Water Depth Effect: Numerical Simulation Results, 72 8.6 Maximum Shear Stress Equation for Contraction Scour, 72 76 CHAPTER 9 The SRICOS-EFA Method for Complex Pier Scour and Contraction Scour in Cohesive Soils 9.1 Background, 76 9.2 The Integrated SRICOS-EFA Method: General Principle, 76 9.3 The Integrated SRICOS-EFA Method: Step-by-Step Procedure, 76 9.4 Input for the SRICOS-EFA Program, 81 9.5 The SRICOS-EFA Program, 81 9.6 Output of the SRICOS-EFA Program, 84 85 CHAPTER 10 Verification of the SRICOS-EFA Method 10.1 Background, 85 10.2 Mueller (1996) Database: Pier Scour, 85 10.3 Froehlich (1988) Database: Pier Scour, 85 10.4 Gill (1981) Database: Contraction Scour, 85 10.5 Remarks, 88 89 CHAPTER 11 Future Hydrographs and Scour Risk Analysis 11.1 Background, 89 11.2 Preparation of the Future Hydrographs, 89 11.3 Risk Approach to Scour Predictions, 90 11.4 Observations on Current Risk Levels, 91 93 CHAPTER 12 Scour Example Problems 12.1 Example 1: Single Circular Pier with Approaching Constant Velocity, 93 12.2 Example 2: Single Rectangular Pier with Attack Angle and Approaching Hydrograph, 93 12.3 Example 3: Group Rectangular Piers with Attack Angle and Approaching Constant Velocity, 95 12.4 Example 4: Contracted Channel with 90-Degree Transition Angle and Approaching Constant Velocity, 99 12.5 Example 5: Contracted Channel with 60-Degree Transition Angle and Approaching Hydrograph, 103 12.6 Example 6: Bridge with Group Piers and Contracted Channel with Hydrograph in Contracted Section, 105

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111 CHAPTER 13 Conclusions and Recommendations 13.1 Conclusions, 111 13.2 Recommendations, 113 114 REFERENCES 116 NOMENCLATURE 118 UNIT CONVERSIONS A-1 APPENDIX A Photographs from the Flume Tests