An evaluation of empirical equations for assessing local scour around bridge piers using global sensitivity analysis

TL;DR

This study evaluates the accuracy of eight empirical equations for assessing bridge pier scour depths using a global sensitivity analysis, highlighting key parameters influencing predictions and identifying the most reliable equations for field conditions.

Contribution

It compares multiple scour equations with field data and applies global sensitivity analysis to identify key parameters, providing insights into their relative importance and accuracy.

Findings

CIRIA and Froehlich equations are most accurate for field conditions.

Angle of attack, pier shape, and approach flow depth are the most influential parameters.

Global sensitivity analysis offers more comprehensive insights than one-at-a-time methods.

Abstract

Bridge scour is a complex phenomenon combining hydrological, geotechnical and structural processes. Bridge scour is the leading cause of bridge collapse, which can bring catastrophic consequences including the loss of life. Estimating scour on bridges is an important task for engineers assessing bridge system performance. Overestimation of scour depths during design may lead to excess spendings on construction whereas underestimation can lead to the collapse of a bridge. Many empirical equations have been developed over the years to assess scour depth at bridge piers. These equations have only been calibrated with laboratory data or very few field data. This paper compares eight equations including the UK CIRIA C742 approach to establish their accuracy using the open access USGS pier-scour database for both field and laboratory conditions. A one-at-the-time sensitivity assessment and a global sensitivity analysis were then applied to identify the most significant parameters in the eight scour equations. The paper shows that using a global approach, i.e. one where all parameters are varied simultaneously, provides more insights than a traditional one-at-the-time approach. The main findings are that the CIRIA and Froehlich equations are the most accurate equations for field conditions, and that angle of attack, pier shape and the approach flow depth are the most influential parameters. Efforts to reduce uncertainty of these three parameters would maximise increase of scour estimate precision.