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Use of Sacrificial Embankments to Prevent Bridge Collapse Due to Scour Under Extreme Events Author: Matthew Brand Mentors: Donna Rizzo, Mandar Dewoolkar, Dryver Huston, Ian Anderson, Jon Lens Findings ABSTRACT The leading cause of highway bridge failure in the United States is bridge scour. High flow events in streams lead to foundational bridge scour by enhancing erosion and scour processes. These bridges are at a critical risk of collapsing during extreme flooding events, and are a major risk to human life and economic sustainability. Currently, agencies and designers have limited resources to predict the increasing severity of flooding that has occurred over the last five decades. Retrofitting the thousands of undersized and scour critical bridges throughout the country to the current standards is prohibitively expensive, and current countermeasures inadequately address the core problems related to scour. Recent research efforts on scour are geared towards modeling and pattern analysis for designing standards for newly built or planned bridges. Very limited research is focused on the design or retrofit standards for the tens of thousands of bridges already built, yet still vulnerable to scour. This research focused on the design and implementation of a simple and effective retrofit for bridges already built using an embankment system that acts as a “fuse” during high flow events. This embankment design increases the streams cross sectional area during high flow events, thereby decreasing the energy and scour potential. This research can provide a more inexpensive, safer, and quicker retrofit for vulnerable bridges compared to current methods. Figure 1: Physical model of bridge abutment with erodible embankment post 100 year storm simulated in 6x1 meter flume in Votey Hall. Figure 2: Physical model of bridge abutment with non-erodible embankment post 100 year storm simulated in 6x1 meter flume in Votey Hall. Bridge S cour RS = 3.5 Bridge S cour RS = 3.5 510 510 Legend Legend WS Q100 WS Q100 Ground Ground Levee Levee 500 Bank Sta 500 Ineff Contr Scour Bank Sta Total Scour Contr Scour Total Scour 490 490 480 Approach Elevation (ft) Elevation (ft) 480 470 470 460 460 450 • Accurately calculating future design storms for bridges and culverts is very difficult 450 440 440 800 • Sought out innovative approaches to reduce bridge scour accounting for future uncertainty • Based on interview with FEMA consultant decided to create new “fuse” embankment design • Designed physical and computational experiments to determine effectiveness of design • Analyzed effectiveness of experiments quantitatively 1000 1200 1400 1600 1800 430 800 1000 Station (ft) Figure 3: Computer simulation of abutment scour in response to 100 year storm using HEC-RAS with fuse system. Scour depth = 25ft 1200 1400 1600 1800 Station (ft) Figure 3: Computer simulation of abutment scour in response to 100 year storm using HEC-RAS with traditional embankment. Scour depth = 35ft Summary Special Thanks • Due to climate change, extreme storm events are happening with greater frequency and magnitude. • The Transportation Research Center for funding this research. • Lengthening existing bridges is not an economically feasible solution. • My mentors and advisors for their support and guidance • New design acts a “fuse” during extreme storm events and embankment fuse is an order of magnitude cheaper to repair than scour. • Embankment fuse reduced scour during a 100 year storm event significantly enough that collapse due to scour could be avoided. References • Arneson, L.A., Zevenbergen, L.W., Lagasse, P.F., & Clopper, P.E. (2012) “Evaluating scour at bridges”, No. FHWA-HIF-12-003 • Kattell, John, P.E., and Merv Eriksson, P.E. "Bridge Scour Evaluation: Screening, Analysis, & Countermeasures." US Forest Service (1998): n. pag. Web. 11 Oct. 2014. • Laursen, E.M., & Toch, A. (1956). “Scour around bridge piers and abutments (Vol. 4)”. Ames, Iowa: Iowa Highway Research Board. • Walsh, J., et. al. 2014: Ch. 2: Our Changing Climate Change Impacts in the United States: The Third National Climate Assessment, J. M. Melillo, Terese (T.C.) Richmond, and G.W. Yohe, Eds., U.S. Global Change Research Program, 19-67. doi: 10.7939/J0KW5CXT.