American Society of Civil Engineers


Revisiting the HEC-18 Scour Equation


by Timothy Calappi, (Graduate student, Department of Civil and Environmental Engineering, Wayne State University, 5050 Anthony Wayne Drive, 2100 Engineering Building, Detroit, MI 48202. E-mail: tcalappi@wayne.edu), Carol J. Miller, P.E., (Professor and Chair, Department of Civil and Environmental Engineering, Wayne State University, 5050 Anthony Wayne Drive, 2100 Engineering Building, Detroit, MI 48202. E-mail: cmiller@eng.wayne.edu), and Donald Carpenter, (Associate Professor, Department of Civil and Environmental Engineering, Lawrence Technological University, 21000 W. Ten Mile Road, Southfield, MI 48075-10588. E-mail: carpenter@ltu.edu)
Section: FHWA Equations and Design Standards, pp. 1102-1109, (doi:  http://dx.doi.org/10.1061/41147(392)111)

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Document type: Conference Proceeding Paper
Part of: Scour and Erosion
Abstract: Accurate pier scour predictions are essential to the safe and efficient design of bridge crossings. Current practice uses empirical formulas largely derived from laboratory experiments to predict local scour depth around single-bridge piers. These formulas have two problems. First, they are hindered by scaling effects; second, they do not consider detailed hydrodynamic forces at work in the scour process. These formula deficiencies can often produce excessive over prediction of scour depths that can lead to unnecessary construction costs. In an effort to improve the predictive capabilities of the HEC-18 scour model, this work uses field-scale data and nonlinear regression to develop a family of equations optimized for various non-cohesive soil conditions. Improving the predictive capabilities of well-accepted equations will save scarce project dollars without sacrificing safety. To help improve acceptance of modified equations, the familiar form of the HEC-18 equation is maintained. When compared to the HEC-18 local pier scour equation, this process reduced the mean square error of a validation data set while maintaining over prediction.


ASCE Subject Headings:
Scour
Bridges
Design
Erosion