Scour at Bridge Foundations on Rock (2012)

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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 717 Scour at Bridge Foundations on Rock Jeffrey R. Keaton AMEC EnvironMEnt & infrAstruCturE, inC. Los Angeles, CA Su K. Mishra HDr EnginEEring, inC. Folsom, CA Paul E. Clopper AyrEs AssoCiAtEs, inC. Fort Collins, CO Subscriber Categories Bridges and Other Structures • Geotechnology • Hydraulics and Hydrology TRANSPORTAT ION RESEARCH BOARD WASHINGTON, D.C. 2012 www.TRB.org 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. 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 Department of Transportation. The Transportation Research Board of the National Academies was requested by the Association to administer the research program because of the Board’s recognized objectivity and understanding of modern research practices. 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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. The needs for highway research are many, and the National Cooperative Highway Research Program can make significant contributions to the solution of highway transportation problems of mutual concern to many responsible groups. The program, however, is intended to complement rather than to substitute for or duplicate other highway research programs. Published reports of the NATIONAL COOPERATIVE HIGHWAY RESEARCH PROGRAM are available from: Transportation Research Board Business Office 500 Fifth Street, NW Washington, DC 20001 and can be ordered through the Internet at: http://www.national-academies.org/trb/bookstore Printed in the United States of America NCHRP REPORT 717 Project 24-29 ISSN 0077-5614 ISBN 978-0-309-21411-7 Library of Congress Control Number 2012938136 © 2012 National Academy of Sciences. All rights reserved. COPYRIGHT INFORMATION Authors herein are responsible for the authenticity of their materials and for obtaining written permissions from publishers or persons who own the copyright to any previously published or copyrighted material used herein. Cooperative Research Programs (CRP) grants permission to reproduce material in this publication for classroom and not-for-profit purposes. 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The report was reviewed by the technical panel and accepted for publication according to procedures established and overseen by the Transportation Research Board and approved by the Governing Board of the National Research Council. The opinions and conclusions expressed or implied in this report are those of the researchers who performed the research and are not necessarily those of the Transportation Research Board, the National Research Council, or the program sponsors. The Transportation Research Board of the National Academies, the National Research Council, and the sponsors of 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 the report.

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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 CRP STAFF FOR NCHRP REPORT 717 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 Hilary Freer, Senior Editor NCHRP PROJECT 24-29 PANEL Field of Soils and Geology—Area of Mechanics and Foundations William Oliva, Wisconsin DOT, Madison, WI (Chair) Larry A. Arneson, Federal Highway Administration, Lakewood, CO Matthew Balmer, New York State DOT, Albany, NY Jerry A. DiMaggio, Transportation Research Board, Washington, DC Michael Fazio, City of Bluffdale, Bluffdale, UT George Machan, Landslide Technology, Portland, OR Mohammed A. Mulla, North Carolina DOT, Raleigh, NC Steve Ng, California DOT, Sacramento, CA Rick Renna, Florida DOT, Tallahassee, FL A. Keith Turner, Colorado School of Mines, Golden, CO Kornel Kerenyi, FHWA Liaison G. P. Jayaprakash, TRB Liaison

This report provides a methodology for estimating the time rate of scour and the design scour depth for a bridge founded on rock, as well as design and construction guidelines for application of the methodology. It will be of interest to hydraulic, bridge, and geotechnical engineers responsible for designing bridge foundations on rock or maintenance engineers concerned about existing bridges founded on erodible rock. Current methodology for scour prediction around bridge foundations considers rock as either “erodible” or “non-erodible.” Equations for scour in sand typically are used to predict scour depths in erodible rock based on hydraulic loading associated with peak dis- charge. As a consequence, predictions of scour in erodible rock frequently seem to over- estimate the extent and depth of scour. Resulting elevations for piers and abutments on erodible rock may be established at levels that require unnecessary, very expensive, and difficult excavation. Some rock types degrade rapidly in changing moisture conditions (e.g., slaking siltstone and shale that shrink, swell, and disintegrate) to produce rock fragments that are highly susceptible to transportation by flowing water. Available scour prediction methods do not permit differentiation among rock types that behave in fundamentally different ways. Scour in fractured or degradable rock is affected by the properties of intact pieces of rock, as well as by the discontinuities in the rock formations. Hydrodynamic forces caused by highly turbulent flow around bridge piers and abutments may remove weakened layers to expose relatively intact rock. These new surfaces may deteriorate in-between flow events and then be susceptible to erosion during a subsequent flood event. Other rock types decompose very slowly so that during the design life of a bridge, intact pieces of rock remain essentially unaltered. Scour in such rock types takes place by displacement, dislodgment, and plucking of rock fragments, especially when large pressure fluctuations are generated in rock dis- continuities caused by turbulent flow around bridge piers. Furthermore, unlike sand-bed channels that respond rapidly to applied hydraulic forces, erodible rock formations tend to wear away gradually and progressively, rather than remaining unaffected by stream flow until a threshold condition (e.g., peak flow velocity) is exceeded. An improved methodology for estimating the rate and design depth of scour in rock over the service life of a bridge is needed. Guidelines that address design issues as well as site-investigation sampling and testing protocols are needed to assist practitioners in apply- ing the methodology. Also, construction guidelines are needed to promote practices that minimize the potential for scour in rock. Under NCHRP Project 24-29, MACTEC Engineering and Consulting undertook to develop a methodology for estimating the time rate of scour and the design scour depth F O R E W O R D By David A. Reynaud Staff Officer Transportation Research Board

of a bridge foundation on rock, and design and construction guidelines for application of the methodology. To accomplish these objectives, the researchers reviewed literature and conducted sur- veys of state and federal agencies on how to quantify hydraulic shear stresses caused by turbulent flow systems around bridge piers and abutments, determine the various prac- tices used for estimating the extent and depth of bridge foundation scour in rock, identify bridges experiencing significant scour in rock, determine geotechnical site-investigation sampling and testing protocols, and determine best practices currently used for construc- tion that minimize the potential for scour in rock. Next, the researchers used their collected information to determine the controlling variables for rock scour based on substructure geometry and on climatic, hydraulic, and geologic characteristics. Their understanding of these controlling variables enabled the researchers to propose a preliminary methodology for determining the rate and design scour depth of a bridge foundation on rock and its pre- liminary sampling and testing protocols. The research team then investigated five existing bridge sites and collected data needed to develop a methodology for determining the time rate of scour and the design scour depth over the expected life of the structure for bridge foundations on rock, validated the methodology, and refined as necessary. Then, they developed design and construction guidelines for applying the methodology, including site-investigation sampling and testing protocols. In the construction guidelines, the researchers also provided best practices that minimize the potential for scour in rock. Finally, the researchers identified topics that deserve further evaluation to address unanswered questions about scour at bridge foundations on rock.

1 Summary 4 Chapter 1 Background and Objectives 4 1.1. Background 5 1.2. Objectives 6 Chapter 2 Research Approach 6 2.1 Overview 7 2.2 Research Plan Modifications 8 2.3 Research Tasks 10 2.4 Report Organization 11 Chapter 3 Findings and Applications 11 3.1 Overview 12 3.2 Findings from the Literature Review 28 3.3 Findings from Survey of State and Federal Agencies 44 3.4 Modes of Rock Scour 70 3.5 Bridge Sites Visited during Project 85 3.6 Event-Based Scour Response 95 3.7 Model Framework 103 3.8 Methodology 146 3.9 Design and Construction Guidelines 157 3.10 Implementation Plan 162 Chapter 4 Conclusions, Recommendations, and Suggested Research 162 4.1 Applicability of Results to Highway Practice 162 4.2 Conclusions and Recommendations 165 4.3 Suggested Research 167 References 172 Symbols and Abbreviations 174 Appendixes C O N T E N T S Note: Many of the photographs, figures, and tables in this report have been converted from color to grayscale for printing. The electronic version of the report (posted on the Web at www.trb.org) retains the color versions.

AUTHOR ACKNOWLEDGMENTS This report was prepared under NCHRP Project No. 24-29 by MACTEC Engineering and Consulting, Inc. (MACTEC); prior to finalization of the report, AMEC Environment & Infrastructure, Inc. (AMEC) acquired MACTEC. AMEC (formerly MACTEC) was the contractor for this study, with Ayres Associ- ates, Inc.; AquaVision Engineering Sàrl; and Haneberg Geoscience, Inc.; as subcontractors. Dr. Jeffrey R. Keaton, P.E., P.G., D.GE, senior principal engineering geologist and vice president at AMEC in Los Ange- les, California, was the project director and principal investigator. Dr. Su K. Mishra, P.E., senior water resources engineer at Ayres Associates in Sacramento, California, was the co-principal investigator; in May 2010, Dr. Mishra left Ayres Associates and joined HDR in Folsom, California. Paul E. Clopper, P.E., senior hydraulic engineer at Ayres Associates in Fort Collins, Colorado, was responsible for the hydrology and hydraulic analyses. Dr. Peter F. Lagasse, P.E., at Ayres Associates in Fort Collins, Colorado, provided advice and review comments, and participated in the Interim Meeting. Dr. Lyle Zevenbergen, P.E., at Ayres Associates in Fort Collins, Colorado, provided advice and participated in internal project meetings. Dr. Erik Bollaert at AquaVision Engineering, Lausanne, Switzerland, modified the Comprehensive Scour Model he devel- oped for high-energy plunging-jet scour for use at bridge sites on typical stream channels. Dr. William C. Haneberg, P.G., at Haneberg Geoscience in Cincinnati, Ohio, developed guidance for characterizing rock discontinuities from conventional vertical borings and estimating in-place sizes of rock blocks from surface measurements and boring data. Dr. Haneberg also logged the boring that was drilled for the project by the Oregon Department of Transportation; he handled the core samples and wrapped them with polyolefin shrink-wrap to preserve moisture because the siltstone was prone to slaking in air. Dr. Jean-Louis Briaud, P.E., geotechnical engineering professor at Texas A&M University in College Station, provided copies of reports regarding scour and invited the principal investigators to visit his laboratory to examine the Erosion Function Apparatus. The success of this research was facilitated by assistance from a number of people affiliated with state departments of transportation, universities, and federal agencies. Mr. Rick Renna, state hydraulics engi- neer with the Florida Department of Transportation, provided access to the State Materials Laboratory in Gainesville and set up a meeting with Dr. Max Shepard and Dr. David Bloomquist at the University of Florida so the principal investigators could examine the Rotating Erosion Test Apparatus and Sediment Erosion Rate Flume. This research project benefitted from Mr. Renna authorizing several samples to be tested in the Rotating Erosion Test Apparatus at no cost to the project. Mr. Renna also provided infor- mation regarding the Interstate Highway 10 Bridge over Chipola River. Dolomite, Inc., a rock products quarry in Marianna, Florida, provided limestone and dolostone samples at no cost to the project. Dr. Stephen E. Dickenson at Oregon State University met with the principal investigators in Eugene to discuss his research on scour of weak rock in the Oregon Coast Range. Dr. Matthew Mabey and Mr. Jan Six at the Oregon Department of Transportation in Salem, Oregon, provided access to, and information about, the State Route 22 Bridge over Mill Creek. Also provided was a drill rig for a boring to obtain core samples of the bedrock at no cost to the project. Mr. George Machan, geotechnical engineer with Landslide Technology in Portland, Oregon, met the principal investigators at the SR-22 Bridge and discussed the investigation plan. Mr. Mike Vierling, engineering geologist with the New York State Thruway Authority, provided access to the Interstate Highway 90 Bridge over Schoharie Creek and led the principal investigators in the field to see the channel conditions at the I-90 Bridge and the SR-161 Bridge located about 4 miles upstream of I-90. Gerard Butch and Ken McGrath at the U.S. Geological Survey Water Resources Office in Troy, New York, provided the Burtonsville Gage data and led the principal investigators to the Burtonsville Gage site. Mr. Matthew Balmer, engineering geologist with the New York State Department of Transportation, arranged for borings to be drilled at the I-90 Bridge at no cost to the project. Mr. Michael Fazio, hydraulic engineer and manager of the Hydraulics Section of the Utah Department of Transportation in Salt Lake City, provided information about, and access to, the SR-262 Bridge over Montezuma Creek. He participated in a field trip to the bridge, described the construction and scour his-

tory, and allowed members of the research team to ride in the state’s airplane to simplify access to the site in southeast Utah. Mr. Steve Ng, senior bridge engineer with the California Department of Transportation in Sacramento, drove the principal investigators to the SR-273 Bridge over Sacramento River in Redding, California, and provided information about, and access to, the bridge. Mr. Steve Thorne, senior hydraulic engineer with the California Department of Transportation in Redding, identified the SR-273 Bridge as a candidate for inclusion in this research and accompanied the principal investigators in the field. Mr. Muhammed Luqman, engineering geologist with the California Department of Transportation in Sacramento, also accompanied the principal investigators during the field examination of the bridge and provided copies of geologic and geotechnical data regarding design and construction of the bridge. Mr. Kevin Flora, senior bridge engineer with the California Department of Transportation in Sacramento, provided hydraulic data and calculations regarding the bridge and provided review comments on the analysis.