Combining Individual Scour Components to Determine Total Scour (2018) / Chapter Skim
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SUMMARY PROJECT DESCRIPTION The objective of this research project is to determine the relationships among individual scour components observed in the same flow event at a bridge, and determine how to combine them to produce realistic estimates of total scour depth for safe and economical design of bridge foundations. The scour components of interest are lateral contraction scour, abutment scour, vertical contraction or pressure scour, and local pier scour.
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2 Numerical modeling of the velocity and flow fields causing scour was accomplished by employing a range of computational fluid dynamics (CFD) models as an integral component of the research plan.
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3 independent variables for these scour components are the following: flow intensity, defined as the ratio of approach flow velocity to its critical value for incipient sediment motion (V1/Vc) ; backwater ratio given by the ratio of the approach flow depth to the unconstricted value at the bridge section (Y1/Yo)
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4 excess pier scour caused by the abutment in addition to the calculated isolated pier scour under the same flow conditions. The excess pier scour was found to depend on the same variables as Category I abutment/embankment scour and on the distance of the pier from the abutment.
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5 EVALUATION A summary of the recommended scour prediction equations and their uncertainties is given in Table 4-7 on the next page. This table shows that scour interactions produce less scour than predicted by current methods of adding individual scour components in Categories I, II, and III.
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6 Table 4-7. Summary of proposed combined scour equations and prediction errors.
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Table 4-7, continued Note: * these values are for ±20 percentage from line of agreement, *
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