Evaluation of Bridge-Scour Research: Abutment and Contraction Scour Processes and Prediction (2011) / Chapter Skim
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9 CHAPTER 1 INTRODUCTION This report reviews the present state of knowledge regarding bridge-abutment scour and evaluates the leading methods currently used for estimating design scour depth. It focuses on research information obtained since 1990, which is to be considered in updating the scour estimation methods that are recommended by AASHTO2 , and used generally by engineering practitioners.
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10 Abutment scour herein is taken to be scour at the bridge-opening end of an abutment, and directly attributable to the flow field developed by flow passing around an abutment. It includes the effects of flow acceleration due to channel flow constriction as well as local largescale turbulence effects due to flow separation which are present in varying relative proportions depending on the upstream approach flow distribution and flow distribution at the bridge section; abutment column type, foundation type and location; flow curvature; and near-field river morphology.
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11 Figure 1-1. Schematic of long, multi-span bridge over a compound channel.
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12 Figure 1-3. Abutment scour resulting in embankment failure by collapse due to geotechnical instability.
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13 The threat posed by scour was realized early in the struggle to construct and maintain bridges. Over the ages it has been dealt with in several ways, but the threat has not yet been adequately addressed.
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14 1.3 OBJECTIVES The principal objectives of this review are as follow: 1. Complete a critical evaluation of knowledge about abutment scour processes, using especially research conducted since 1990; 2.
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