United States Department of Transportation
i
Submerged flow bridge scour under clear water conditions
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2012-09-01
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[PDF-1.39 MB]
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Edition:Laboratory report; May 2010-June 2012.
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NTL Classification:NTL-HIGHWAY/ROAD TRANSPORTATION-Bridges and Structures;NTL-HIGHWAY/ROAD TRANSPORTATION-Soils and Geology;
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Abstract:Prediction of pressure flow (vertical contraction) scour underneath a partially or fully submerged bridge superstructure
in an extreme flood event is crucial for bridge safety. An experimentally and numerically calibrated formulation is
developed for the maximum clear water scour depth in non-cohesive bed materials under different approach flow and
superstructure inundation conditions. The theoretical foundation of the scour model is the conservation of mass for
water combined with the quantification of the flow separation zone under the bridge deck superstructure. In addition to
physical experimental data, particle image velocimetry measurements and computational fluid dynamics simulations
are used to validate assumptions used in the derivation of the scour model and to calibrate parameters describing the
separation zone thickness. With the calibrated model for the separation zone thickness, the effective flow depth
(contracted flow depth) in the bridge opening can be obtained. The maximum scour depth is calculated by identifying
the total bridge opening that creates conditions such that the average velocity in the opening, including the scour depth,
is equal to the critical velocity of the bed material. Data from previous studies by Arneson and Abt and Umbrell et al.
are combined with new data collected as part of this study to develop and test the proposed formulation.
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