Evaluation of Bridge Scour Research: Pier Scour Processes and Predictions (2011) / Chapter Skim
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1 EXECUTIVE SUMMARY Introduction This report evaluates the current state of knowledge regarding bridge-pier scour, assesses leading methods for reliable design estimates of scour depth, proposes a structured methodology for scour-depth estimation for design purposes, and indicates pier-scour aspects in need of further research. It focuses particularly on research information obtained since 1990, showing that this information provides considerable new insights that compel the need to change the design method currently recommended by the principal authoritative design guides (notably FHWA's HEC-181, and AASHTO2 )
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2 2. Summarize the state of knowledge on bridge-pier scour processes, doing so in a way that explains how variations in the flow, sediment, and geometrical variables (thereby the main design parameters)
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3 3. Because considerable uncertainty attends flow conditions and boundary material at bridge waterways, design prudence requires estimation of a potential maximum scour depth, rather than scour-depth prediction.
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4 i. The roles of variables and parameters defining pier scour processes; ii.
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5 y/a, which indicates the geometric scale of the pier flow field in terms of approach-flow depth, y, and pier width, a a/D, which relates the length scales of pier width and median diameter of bed particle, D Ω, a/b, and θ , which define pier face shape, aspect ratio of pier crosssection (face width/ pier length) , and approach flow alignment to pier, respectively.
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6 y/a and a/D. A useful aspect of the Sheppard-Melville method is that it can be simplified to reflect potential maximum scour depth associated with the three pier flow-field categories (narrow, transition, and wide)
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7 submergence) Consider hydraulic model to validate scour-depth estimate iv.
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8 For understanding scour processes, no research topics are identified as critical priority, though several are of high priority, all of which concern improved understanding of how site complications affect pier flow field: i. Debris accumulations; ii.
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