Evaluation of Bridge Scour Research: Pier Scour Processes and Predictions (2011) / Chapter Skim
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19 CHAPTER 2 SCOUR AS A DESIGN CONCERN 2.1 Introduction When considering pier scour, it is necessary to consider pier structure and its influence on the scouring flow field, the foundation material supporting the pier, and the processes whereby flow erodes foundation material (sediment, soil, clay, rock) around the pier.
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20 More complicated and unique pier forms often are required for less common bridge sites, such as for large bridges, and channel circumstances where piers must withstand additional loads. Bridges in large tidal flows, flows subject to dynamic ice conditions, and bridges possibly subject to vessel impact, for example, require more complicated piers.
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21 Figure 2-3 A common pier form in a flow situation complicated by debris or ice accumulation Figure 2-4 Some bridges, such unusually large bridges, or bridges in unusual circumstances, require large piers of uncommon design 2.3 Design Depth for Pier Foundation The design scour depth must be taken into account when sizing and positioning the foundation base. For piers on spread footings, the top of the footing must be below the estimated design scour depth, so that the footing is not undermined.
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22 bearing piles, pile length must include design scour depth so as to ensure sufficient friction length of pile (Figure 2-5)
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24 Figure 2-7 Bridge pier settled vertically owing to scour reduction of pier support (a)
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25 Other methods may be used regionally, though in conjunction with the HEC-18 method; e.g., the method developed by Wilson (1995) who uses extensive field data from bridges in Mississippi.
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26 As the present report explains, the approach is not entirely new. Chapter 5 shows several methods that attempt to account for the influences of major parameters.
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27 Hydraulic Research [JHR]
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28 Figure 2-9 Overview of structured design approach
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