United States Department of Transportation
i
Allowable Limit Contraction and Abutment Scour at Bridges: Technical Report
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2019-05-01
[PDF-3.66 MB]
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Alternative Title:Allowable Limit Contraction Scour and Abutment Scour at Bridges
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Edition:Technical Report, September 2016–August 2018
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Abstract:Scour at bridges is the leading cause of bridge failures. While research efforts mostly focus on the prediction of the scour depth at bridge supports, little to no attention is given to the determination of maximum allowable scour depth at bridges. Providing scour countermeasures at all existing bridges to ensure acceptable scour resistance is economically unfeasible. Consequently, guidelines on the maximum allowable scour depth become a crucial tool to make risk informed decisions ensuring public safety at the minimum cost possible. Such guidelines result in site-specific values of scour limits to be compared with the measured or calculated scour at an existing bridge for the purpose of making a preliminary judgment of the scour criticality at that bridge and assessing the need for advanced structural and geotechnical analyses. Scour limits depend on the stability of the bridge foundations at piers and abutments. The Texas Department of Transportation already has guidance for the determination of the maximum allowable scour depth at piers with pile or drilled shaft foundations. This project proposes guidelines on the determination of the maximum allowable scour depth at or near spill-through abutments, where the failure scour depth is controlled by the slope stability of the abutment embankment. Over 50,000 slope stability simulations are performed to find the failure scour depth of abutments with different geometries and soil types, under the most critical condition of rapid drawdown. The analyses resulted in linear relationships between failure scour depth and soil shear strength parameters. Practical recommendations for the immediate determination of the scour limit at or near spill-through abutments based on the abutment total height, and embankment and channel bed soil types are established. Case studies are used to illustrate the application of these new guidelines and prove their validity.
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