SCOUR AT THE BASE OF RETAINING WALLS AND OTHER LONGITUDINAL STRUCTURES FINAL REPORT Prepared for NCHRP Transportation Research Board of The National Academies Author Dr. Fotis Sotiropoulos Stony Brook University Stony Brook, NY Dr. Panos Diplas Lehigh University Bethlehem, PA April 2017 ACKNOWLEDGEMENT OF SPONSORSHIP This work was sponsored by one or more of the following as noted: X American Association of State Highway and Transportation Officials, in cooperation with the Federal Highway Administration, and was conducted in the National Cooperative Highway Research Program, Federal Transit Administration and was conducted in the Transit Cooperative Research Program, Federal Aviation Administration and was conducted in the Airport Cooperative Research Program, Research and Innovative Technology Administration and was conducted in the National Cooperative Freight Research Program, Pipeline and Hazardous Materials Safety Administration and was conducted in the Hazardous Materials Cooperative Research Program, Federal Railroad Administration and was conducted in the National Cooperative Rail Research Program, which is administered by the Transportation Research Board of the National Academies. DISCLAIMER This is an uncorrected draft as submitted by the Contractor. The opinions and conclusions expressed or implied herein are those of the Contractor. They are not necessarily those of the Transportation Research Board, the National Academies, or the program sponsors. Contents Contents .......................................................................................................................................... ii List of Figures ................................................................................................................................ iii Author Acknowledgements ........................................................................................................... iv Abstract ........................................................................................................................................... 1 Executive Summary ........................................................................................................................ 2 1 Introduction ............................................................................................................................. 3 2 Background .............................................................................................................................. 5 3 Research Approach .................................................................................................................. 6 4 Compilation of Experimental and Numerical Results to Develop Scour Relations ................ 7 5 References ............................................................................................................................. 11 Appendix A State of the Art Review Appendix B Practitioner Survey Appendix C Large-scale physical experiments Appendix D Small-scale physical modeling Appendix E Numerical model validation and simulation results Appendix F List of Variables ii List of Figures Figure 1: Illustration of overturning and structure failure of a retaining wall due to scour along the base. Figure 2: Schematic of cross-section at the transition from a sloping bank to rectangular section within the retaining wall area. Flow direction out of the paper. Figure 3: Regression equation to estimate maximum scour depth due to local scour at the leading edge of the retaining wall. Figure 4: Schematic of the installation angles ( ) of the longitudinal wall in the meandering river Figure 5: Maximum scour depth data obtained from large-scale experiments and numerical simulations (dots) for general scour and the regression equation overlapping the data points (dashed-line). r2 of the regression is 0.821. iii Author Acknowledgements The research reported herein was performed under NCHRP Project 24-36 by the St. Anthony Falls Laboratory at the University of Minnesota. Lehigh University and the Virginia Polytechnic Institute and State University (Virginia Tech) were subcontractors to the University of Minnesota. Dr. Fotis Sotiropoulos, Professor of Civil Engineering and Director of the St. Anthony Falls Laboratory (SAFL) at University of Minnesota, currently dean of College of Engineering & Applied Science and Professor of Civil Engineering Department at Stony Brook University, is the Project Director and the Principal Investigator. The other authors of this report are Dr. Panos Diplas, Civil and Environmental Engineering Dept. of Lehigh University, Dr. Ali Khosronejad, Research Associate at SAFL (currently Assistant Professor at Civil Engineering Department of Stony Brook University), Dr. Jessica Kozarek, Research Associate at SAFL, Phairot Chatanantavet, Post-Doctoral Associate at Lehigh University, Nasser Heydari, Ph.D student at Lehigh University, Colleen Turley, M.S. Student at Lehigh University, Polydefkis Bouratsis, Ph.D Student at Virginia Tech, and Nikos Apsilidis Ph.D Student at Virginia Tech. The work was completed under the general supervision of Dr. Fotis Sotiropoulos and Dr. Diplas at Lehigh University. iv Abstract We carried out a series small- and large-scale experiments at Lehigh University and the Outdoor StreamLab (OSL) of University of Minnesota, respectively, to obtain datasets for maximum scour depth at the base of longitudinal walls. These datasets are used to validate the coupled flow and morphodynamics model of Virtual Flow Simulator (VFS-Rivers). The dataset of the small-scale experiments, which contains 64 data points, is employed to present an empirical relationship for maximum scour depth due to local scour near the leading edge of longitudinal walls with different bank and wall configurations. The validated numerical model is run for more than 20 test cases to obtain more data for the maximum scour depth in the large-scale meandering rivers due to general scour. Combining the maximum scour data from large-scale experiments at the OSL (four data points) and numerical simulations (20 data points), we obtained a dataset that was used to produce another empirical relationship to estimate the maximum scour depth at the base of longitudinal walls due to general scour in meandering rivers. The maximum scour depths obtained from the two presented equations can be linearly added to give the total maximum scour depth at the base of longitudinal walls in meandering rivers. The presented equations are valid within a specific range of data for sediment material, flow field, and waterway characteristics. 1 Executive Summary The current state-of-the-art for the scour depth prediction near longitudinal walls is be limited to two empirical equations, which are obtained from a limited number of experimental and field data. These existing methods of prediction do not take into account some important properties of flow, sediment and waterway geometry, including, for instance: median grain size of sediment material, mean-flow depth and velocity, and sinuosity of meandering rivers. To fill the gap and develop a more comprehensive relationship for estimating the total scour depth at the base of longitudinal walls, we carried out a series of experimental (large- and small-scale) and numerical investigations encompassing most of the important characteristics of the sediment, flow and waterway geometry. In these investigations, we studied the effect of turbulence, sediment material, roughness of the structures, and river geometry on the scour depth at the base of longitudinal walls. A series of small-scale laboratory experiments were conducted at Lehigh University to produce 64 data points for the local scour depth occurring at the leading edge of longitudinal walls. Based on these data points, we obtained a relationship for estimating the maximum scour depth in the vicinity of longitudinal walls due to local scour process. This dataset was also used to validate the numerical model. A series of large-scale experiments were also carried out at the Outdoor StreamLab of St. Anthony Falls Laboratory at the University of Minnesota to produce large-scale physical data for the validations of numerical model. The large-scale experiment data (four data points) were also combined with 20 data points obtained from numerical simulations to develop a relationship for estimating the maximum scour depth at the base of longitudinal walls due to general scour. The total maximum scour depth at the base of longitudinal walls is considered to be a linear combination of local and general scours. Thus, the scour depth values obtained from the two equations for the local and general scours, respectively, can be linearly combined to obtain the total maximum scour depth at the base of longitudinal walls in meandering waterways. 2 1 Introduction Longitudinal walls are widely used to enhance the slope stability of earth material and protect bridge abutments and other longitudinal structures that encroach into waterways. When installed at riverbanks, their base becomes subject to erosion due to the action of water. Even partial exposure of the foundation may result in the failure of the longitudinal wall. Thus, longitudinal walls on the river banks require to be protected against scour that can lead to structure undermining and failure by designing and installing countermeasures to mitigate erosion along the face and/or at the bottom of the structure. In meandering rivers flowing through urban areas or along roadways, retaining walls are commonly used