United States Department of Transportation
i
Development of New Design Guidelines for Protection Against Erosion at Bridge Abutments and Embankments-Phase I
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2018-12-01
[PDF-2.95 MB]
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Edition:Final Report
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Abstract:Over the last two decades, the United States Midwest has experienced increasingly catastrophic flood events. Severe erosion problems occurred even though the erosion protection design measures for bridge abutments and their embankments followed the existing guidelines (e.g., HEC 23, 2001 and following updates through 2009). The methodology proposed to estimate design variables in scour protection measure formulas (e.g., size of riprap stone) for these guidelines at such sites is oversimplified. The present research proposes a numerically-based approach for improving methodologies to design riprap protection measures at wing-wall and spill-through abutments. The mean flow fields and the bed shear stress distributions predicted using high-resolution, fully three-dimensional (3-D), non-hydrostatic RANS simulations were used to estimate the maximum bed shear stress over the riprap layer, the shear-failure entrainment threshold for the riprap stone and the other variables in the design formulas recommended in HEC 23 (Lagasse et al., 2001). The numerically-based approach was successfully validated for the case of wing-wall abutments placed in a straight channel. Simulations were also conducted for spill-through abutments with varying floodplain width, ratio of abutment length to floodplain width, and riprap stone size. The simulations demonstrated the critical Froude number corresponding to the entrainment threshold decreases monotonically with increasing La/Bf or La/yf (Bf=floodplain width, La=abutment length, yf=flow depth over floodplain). Modifications are proposed to the standard Lagasse et al. (2001) formula that ensure the (modified) design formula is applicable to a range of flow and geometrical parameters. There is a need for further research to determine the range of applicability of the standard design formulas such that they can be applied to more complex cases.
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Content Notes:URL to final dataset for the research project: http://doi.org/10.13014/K2C24TN4
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