Effects of Debris on Bridge Pier Scour (2010)

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TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2010 www.TRB.org N A T I O N A L C O O P E R A T I V E H I G H W A Y R E S E A R C H P R O G R A M NCHRP REPORT 653 Subscriber Categories Bridges and Other Structures • Geotechnology • Hydraulics and Hydrology Effects of Debris on Bridge Pier Scour P. F. Lagasse P. E. Clopper L. W. Zevenbergen W. J. Spitz L. G. Girard AYRES ASSOCIATES, INC. Fort Collins, CO Research sponsored by the American Association of State Highway and Transportation Officials in cooperation with the Federal Highway Administration

NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM Systematic, well-designed research provides the most effective approach to the solution of many problems facing highway administrators and engineers. Often, highway problems are of local interest and can best be studied by highway departments individually or in cooperation with their state universities and others. However, the accelerating growth of highway transportation develops increasingly complex problems of wide interest to highway authorities. These problems are best studied through a coordinated program of cooperative research. 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. 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CRP STAFF FOR NCHRP REPORT 653 Christopher W. Jenks, Director, Cooperative Research Programs Crawford F. Jencks, Deputy Director, Cooperative Research Programs David A. Reynaud, Senior Program Officer Megan A. Chamberlain, Senior Program Assistant Eileen P. Delaney, Director of Publications Natalie Barnes, Editor NCHRP PROJECT 24-26 PANEL Field of Soils and Geology—Area of Mechanics and Foundations William Oliva, Wisconsin DOT, Madison, WI (Chair) Brian L. Beucler, Federal Highway Administration, Sterling, VA Merril E. Dougherty, Indiana DOT, Indianapolis, IN Robert Ettema, University of Wyoming, Laramie, WY Kevin Scott Flora, California DOT, Sacramento, CA James Lane, New Jersey DOT, Trenton, NJ Jon K. Zirkle, Tennessee DOT, Nashville, TN David D. Zwernemann, Texas DOT, Austin, TX Kornel Kerenyi, FHWA Liaison Frank N. Lisle, TRB Liaison C O O P E R A T I V E R E S E A R C H P R O G R A M S

This report provides guidelines for practitioners to estimate the quantity of accumulated, flow event debris, based on the density and type of woody vegetation and river bank condi- tion upstream and analytical procedures to quantify the effects of resulting debris-induced scour on bridge piers. The report should be of interest to bridge engineers, maintenance personnel and operations staff at state and local agencies. As every organization that designs, operates, and maintains bridges is well aware, bridge scour is a problem that can have catastrophic effects. It is well known, since the 1980 col- lapse of a part of the Perkins Road Bridge over Nonconnah Creek in Memphis, Tennessee, that the accumulation of floating debris in the form of tree trunks and limbs during flood events plays a critical role in the occurrence of scour at bridge piers. In the investigation that followed the Perkins Road collapse, engineers found that a 20% blockage between piers would alter flow conditions and undermine the 12 ft of embedment on the piles support- ing the pier that failed. The best information to provide to these bridge owners, to help them cut this problem down to manageable size, is improved prediction techniques to foresee the development and shape of debris accumulation and the resulting extent of scour at the bridge piers. This research performed by Ayres Associates Inc. under NCHRP Project 24- 26, “Effects of Debris on Bridge Pier Scour,” provides methods to create these prediction techniques. The research methods employed during the course of this study include a literature review, a survey of bridge owners to determine current practices, and creation of a photo- graphic archive to help predict the size and shape of accumulated debris. Results of a flume study are provided to establish relationships between the size and shape of accumulated debris and the resulting pier scour. These methods are all illustrated by example problem solutions and case studies to facilitate understanding. In addition to this published report, the debris photographic archive, the survey questionnaire and list of respondents, and the report on the field pilot study are available on the TRB website (www.trb.org) as NCHRP Web-Only Document 148 (search for “NCHRP Web-Only Document 148”). F O R E W O R D By David A. Reynaud Staff Officer Transportation Research Board

AUTHOR ACKNOWLEDGMENTS This work was sponsored by the American Association of State Highway and Transportation Officials (AASHTO), in cooperation with the Federal Highway Administration (FHWA), and was conducted through the National Cooperative Highway Research Program (NCHRP), which is administered by the Transportation Research Board (TRB) of the National Academies. The research reported herein was performed under NCHRP Project 24-26 by Ayres Associates Inc., Fort Collins, Colorado. Dr. P.F. Lagasse, Senior Vice President, served as Principal Investigator and Mr. P.E. Clopper, Senior Water Resources Engineer, served as Co-Principal Investigator. They were assisted by Dr. L.W. Zevenbergen, Manager River Engineering; Mr. W. J. Spitz, Senior Geomorphologist; and Ms. L.G. Girard, Hydraulic Engineer. Mr. G.R. Price of ETI Instrument Systems, Fort Collins, Colorado, provided support for adapting the instrumentation for the articulated arm to measure the geometry of debris clusters and accompanied the research team on the field pilot study in Kansas. A special acknowledgment is due Mr. Bradford Rognlie, Bridge Squad Leader, Kansas Department of Transportation (DOT), for his enthusiastic response to the survey, his invaluable support for the field pilot study of debris-prone bridges in Kansas, and his interest throughout the project. The core of the photographic archive in Appendix A, which provided a cost- effective substitute for extensive field work, was provided by Mr. Mike Collier, Debris Free, Inc., Ojai, Cal- ifornia, from a collection of photographs he assembled during site visits around the United States. The research team would also like to thank the 88 respondents to the survey, which included 30 state DOTs and Puerto Rico. Your interest underscores the pervasive nature of the debris problem at bridges. Hope- fully the results of this research will justify the time you invested in your responses. We must also recog- nize the pioneering work by Mr. Tim Diehl of the United States Geological Survey and Dr. Bruce Melville and Mr. D.M.S. Dongol of the University of Auckland, New Zealand, that provided the foundation for the advances made in this study. All laboratory testing was performed at the Colorado State University Engineering Research Center Hydraulics Laboratory under the direction of Dr. Chris Thornton and Mr. Michael Robison. The assis- tance of Mr. Sean Kimbrel, graduate student; Mr. Matt Stockton, lab technician; and Mr. Mick Ursic, undergraduate student is also acknowledged. The participation, advice, and support of NCHRP Project 24-26 panel members throughout this project are gratefully acknowledged.

C O N T E N T S 1 Summary 4 Chapter 1 Introduction and Research Approach 4 1.1 Scope and Research Objectives 4 1.1.1 Background 4 1.1.2 Objectives 5 1.2 Research Approach 5 1.2.1 Overview 6 1.2.2 Research Plan Modifications 6 1.3 Research Tasks 6 1.3.1 Phase 1 Tasks 7 1.3.2 Phase 2 Tasks 8 1.4 Research Results 8 1.5 Documentation Organization 9 Chapter 2 Findings 9 2.1 Review of Current Practice 9 2.1.1 Introduction 10 2.1.2 Debris Source Loading, Distribution, and Recruitment 11 2.1.3 Debris Transport 15 2.1.4 Debris Deposition, Accumulation, and Storage 17 2.1.5 Debris Accumulation at Bridge Piers 19 2.1.6 Modeling Debris-Induced Hydrodynamic Forces and Scour 21 2.1.7 Managing Debris Accumulations at Bridges 24 2.2 Debris Photographic Archive 24 2.3 Regional Analysis of Debris 34 2.4 Survey and Site Reconnaissance 34 2.4.1 Survey 35 2.4.2 Analysis of Survey Responses 39 2.5 Site Reconnaissance 39 2.5.1 Equipment and Preparation 39 2.5.2 Field Pilot Study 39 2.5.3 Field Pilot Study Results 40 2.5.4 Recommendations 41 Chapter 3 Guidelines, Testing, Appraisal, and Results 41 3.1 Introduction 41 3.2 Guidelines for Assessing Debris Production, Transport Delivery, and Accumulation Potential 42 3.2.1 Phase 1: Evaluate Potential for Debris Production and Delivery 48 3.2.2 Phase 2: Estimate Potential for Debris Accumulation on Individual Bridge Elements 50 3.2.3 Phase 3: Determine the Overall Debris Accumulation Potential for the Bridge

52 3.3 Application of the Guidelines: South Platte River Case Study 52 3.3.1 Field Reconnaissance 53 3.3.2 Development of the Case Study 53 3.4 Development of Debris Characteristics for Laboratory Testing 53 3.4.1 Debris Accumulation Characteristics 58 3.4.2 Laboratory Testing of Debris 60 3.5 Laboratory Testing Program 60 3.5.1 Testing Facilities and Protocols 70 3.5.2 Debris Cluster Test Materials 72 3.5.3 Baseline Tests 76 3.5.4 Tests with Debris 79 3.6 Appraisal of Testing Results 79 3.6.1 Baseline (No-Debris) Tests 85 3.6.2 Tests with Debris 90 3.7 Scour Prediction at Bridge Piers with Debris Loading 90 3.7.1 Introduction 92 3.7.2 Equivalent Pier Width 94 3.7.3 Recommended Design Equation 94 3.7.4 Effect of Debris Roughness and Porosity 94 3.7.5 Effect of Debris Location in the Water Column 96 3.7.6 Lateral Extent of Scour at Piers with Debris 97 3.8 Incorporating Debris in Hydraulic Models 97 3.8.1 HEC-RAS 98 3.8.2 Two-Dimensional Models 99 3.9 Application Methodology and Examples 99 3.9.1 Methodology 100 3.9.2 Example Debris Scour Calculations 102 3.10 Guidelines for Inspection, Monitoring, and Maintenance 102 3.10.1 Inspection 103 3.10.2 Monitoring 104 3.10.3 Maintenance 105 3.11 Implementation Plan 105 3.11.1 The Product 105 3.11.2 The Market 105 3.11.3 Impediments to Implementation 105 3.11.4 Leadership in Action 106 3.11.5 Activities for Implementation 106 3.11.6 Criteria for Success 107 Chapter 4 Conclusions and Suggested Research 107 4.1 Applicability of Results to Highway Practice 107 4.2 Conclusions and Recommendations 107 4.2.1 Overview 108 4.2.2 Advances in the State of Practice 110 4.2.3 Deliverables 111 4.3 Suggested Research 112 References A-1 APPENDIX A Debris Photographic Archive B-1 APPENDIX B Survey of Practitioners C-1 APPENDIX C Field Pilot Study Report D-1 APPENDIX D Field Data Sheets and Case Study