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Monitoring the Effects of Knickpoint Erosion on Bridge Pier and Abutment Structural Damage Due to Scour Thanos Papanicolaou University of Iowa, [email protected]

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Monitoring the Effects of Knickpoint Erosion on Bridge Pier and Abutment Structural Damage Due to Scour Thanos Papanicolaou University of Iowa, Tpapanic@Utk.Edu University of Nebraska - Lincoln DigitalCommons@University of Nebraska - Lincoln Final Reports & Technical Briefs from Mid-America Mid-America Transportation Center Transportation Center 2012 Monitoring the Effects of Knickpoint Erosion on Bridge Pier and Abutment Structural Damage Due to Scour Thanos Papanicolaou University of Iowa, [email protected] David M. Admiraal University of Nebraska-Lincoln, [email protected] Christopher Wilson University of Nebraska-Lincoln Clark W. Kephart University of Nebraska-Lincoln, [email protected] Follow this and additional works at: http://digitalcommons.unl.edu/matcreports Part of the Civil Engineering Commons Papanicolaou, Thanos; Admiraal, David M.; Wilson, Christopher; and Kephart, Clark W., "Monitoring the Effects of Knickpoint Erosion on Bridge Pier and Abutment Structural Damage Due to Scour" (2012). Final Reports & Technical Briefs from Mid-America Transportation Center. 3. http://digitalcommons.unl.edu/matcreports/3 This Article is brought to you for free and open access by the Mid-America Transportation Center at DigitalCommons@University of Nebraska - Lincoln. It has been accepted for inclusion in Final Reports & Technical Briefs from Mid-America Transportation Center by an authorized administrator of DigitalCommons@University of Nebraska - Lincoln. Report # MATC-UI-UNL: 471/424 Final Report 25-1121-0001-471, 25-1121-0001-424 Monitoring the Effects of Knickpoint Erosion ® on Bridge Pier and Abutment Structural Damage Due to Scour A.N. Thanos Papanicolaou, Ph.D. Professor Department of Civil and Environmental Engineering IIHR—Hydroscience & Engineering University of Iowa David M. Admiraal, Ph.D. Associate Professor Christopher Wilson, Ph.D. Assistant Research Scientist Clark Kephart Graduate Research Assistant 2012 A Cooperative Research Project sponsored by the U.S. Department of Transportation Research and Innovative Technology Administration The contents of this report reflect the views of the authors, who are responsible for the facts and the accuracy of the information presented herein. This document is disseminated under the sponsorship of the Department of Transportation University Transportation Centers Program, in the interest of information exchange. The U.S. Government assumes no liability for the contents or use thereof. Monitoring the Effects of Knickpoint Erosion on Bridge Pier and Abutment Structural Damage Due to Scour A.N. Thanos Papanicolaou, Ph.D. Professor Department of Civil and Environmental Engineering IIHR—Hydroscience & Engineering University of Iowa David M. Admiraal, Ph.D. Associate Professor Department of Civil Engineering University of Nebraska–Lincoln Christopher Wilson, Ph.D. Assistant Research Scientist IIHR—Hydroscience & Engineering University of Iowa Clark Kephart Graduate Research Assistant Department of Civil Engineering University of Nebraska–Lincoln A Report on Research Sponsored by Mid-America Transportation Center University of Nebraska-Lincoln April 2012 Technical Report Documentation Page 1. Report No. 2. Government Accession No. 3. Recipient's Catalog No. 25-1121-0001-471 (also reporting for 25-1121-0001-424) 4. Title and Subtitle 5. Report Date Monitoring the effects of knickpoint erosion on bridge pier and abutment April 2012 structural damage due to scour 6. Performing Organization Code 7. Author(s) 8. Performing Organization Report No. A. N. Thanos Papanicolaou, David Admiraal, Christopher Wilson, and Clark 25-1121-0001-471 Kephart (also reporting for 25-1121-0001-424) 9. Performing Organization Name and Address 10. Work Unit No. (TRAIS) Mid-America Transportation Center 2200 Vine St. 11. Contract or Grant No. PO Box 830851 Lincoln, NE 68583-0851 12. Sponsoring Agency Name and Address 13. Type of Report and Period Covered Research and Innovative Technology Administration Final Report 1200 New Jersey Ave., SE July 2010-April 2012 Washington, D.C. 20590 14. Sponsoring Agency Code MATC TRB RiP No. 28504 15. Supplementary Notes 16. Abstract The goal of this study was to conduct a field-oriented evaluation, coupled with advanced laboratory techniques, of channel degradation in a stream of the Deep Loess Region of western Iowa, namely Mud Creek. The Midwestern United States is an ideal place for such a study considering that ~$1 Billion of infrastructure and farmland has been lost recently to channel degradation. A common form of channel degradation in this region is associated with the formation of knickpoints, which naturally manifest as short waterfalls within the channel that migrate upstream. As flow plunges over a knickpoint face, scouring of the downstream bed creates a plunge pool. This downcutting increases bank height, facilitating bank failure, stream widening, and damage to critical bridge infrastructure. We conducted a state-of-the-art geotechnical analysis of the sediments from the knickpoint face, plunge pool, and adjacent stream banks to determine the areas of the streambed near the bridge infrastructure that favor knickpoint propagation. Soil characterization using particle size distributions and Gamma Spectroscopy identified a stratigraphic discontinuity at the elevation where the knickpoint forms. An automated surveillance camera was established to monitor the location of the knickpoint face relative to a fixed datum and provide a first-order approximation of its migration rate, which was approximately 0.9 m over a 248-day study period. Surveys conducted of the stream reach also facilitated information about knickpoint migration. Flow measurements using Large- scale Particle Image Velocimetry were conducted during the study to understand the hydrodynamic conditions at the site. The results of this research will assist local and federal transportation agencies in better understanding the following: (1) principal geotechnical and hydrodynamic factors that control knickpoint propagation, (2) identify necessary data for extraction and analysis to predict knickpoint formation, (3) provide mitigation measures such as grade control structures (e.g., sheet-pile weirs, bank stabilization measures) near bridge crossings to control the propagation of knickpoints and prevent further damage to downstream infrastructure. 17. Key Words 18. Distribution Statement Knickpoint, Scour, Bridge Infrastructure Safety 19. Security Classif. (of this report) 20. Security Classif. (of this page) 21. No. of Pages 22. Price Unclassified Unclassified 51 ii Table of Contents Acknowledgements viii Disclaimer ix Executive Summary x Chapter 1 Introduction 1 1.1 Problem Statement 1 1.2 Definitions 4 1.3 Previous Research 6 Chapter 3 Methodology 10 3.1 Study Site 10 3.2 Core Extraction 11 3.3 Core Parameterization 14 3.4 Knickpoint Propagation Using a Time-Lapse Camera 18 3.5 Knickpoint Propagation Using Survey Data 21 3.6 Flow Velocity Distributions Using LPIV 21 Chapter 4 Results 26 4.1 Geotechnical Analysis 26 4.2 Knickpoint Propagation 35 4.3 Flow Velocity Observations – LPIV 40 Chapter 5 Summary and Conclusions 43 References 49 iii List of Figures Figure 1.1 (a) Channel straightening of Mud Creek, IA in the 1950s. The white line is the original channel. The blue line is the creek after straightening; (b) Channel incision at Mud Creek. 1 Figure 1.2 Knickpoint formation. The circled area is a knickpoint in Mud Creek, IA. 4 Figure 1.3 Knickpoint processes. A sketch of the steps involved in knickpoint migration. 5 Figure 3.1 Mud Creek, IA. The red dot on the aerial photo is the monitored knickpoint. The circle in the site photo highlights the knickpoint. 12 Figure 3.2 Core Collection. Cores from the stream banks near the knickpoint face were collected using a Giddings probe and Shelby tube system. 13 Figure 3.3 Stratigraphic Interpretation. A close-up of the surface section for the stream bank core used in the stratigraphy analysis. The ruler in the image is in inches. 15 Figure 3.4 Gamma Scanner. The gamma scanner system at IIHR. Typical results of a core’s density. 16 Figure 3.5 Measuring Core Bulk Density. A section of the stream bank core was placed in a vertical frame. A 241Am sealed source was moved up and down the core length in conjunction with a gamma energy detector on the other side of the core. The attenuation of the received radioactivity was indication of the core density. 17 Figure 3.6 Time-lapse images collected on (a) September 15, 2011 (b) December 3, 2011, and (c) February 12, 2012. 20 Figure 3.7 Corrected Time-lapse images from (a) September 15, 2011 (b) December 3, 2011, and (c) February 12, 2012. 19 Figure 3.8 LPIV image samples: (a) original image sampled from LPIV video and (b) rectified LPIV image. 23 Figure 3.9 Depiction of subareas associated with interrogation points used for discharge calculations. 24 Figure 4.1 Stratigraphic Discontinuity. There appears to be a stratigraphic discontinuity close to the knickpoint with a darker sediment (in the black circle) overlaying a lighter-colored sediment (in the red circle). 26 Figure 4.2 Particle Size Distribution. These graphs show key particle size diameters of the sampled depth intervals in a stream bank core from the study site. The d16, d50, and d84 for each interval are plotted relative to depth. The red circle highlighting the 600-650 cm depth interval corresponds to a coarsening of the overall particle size distribution, as there are increases in the d50 and d84. This elevation corresponds to the top elevation of the knickpoint face. 28 iv Figure 4.3 Soil Texture. The percentages of clay, silt, and sand for each depth interval of a stream bank core from the study site. The red circle highlighting the 600-650 cm depth interval corresponds to a discontinuity in bank stratigraphy. This discontinuity corresponds to the top elevation of the knickpoint face. 29 Figure 4.4 Soil Ternary Diagram. The soil texture of depth intervals in a stream bank core based on USDA soil classifications and particle size measurements. Red circles represent samples above 600 cm, and blue circles represent samples below 600 cm. The 600-650 cm elevation corresponds to the top elevation of the knickpoint face. There is a coarsening of sediment below this elevation, as seen through a shift in the texture as the material becomes sandier.
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