A study on empirical prediction and monitoring of bridge pier scour depth: implications for asset owners and operators

Abstract

Bridges are infrastructure assets which connect communities and in cases of collapse or reduced service, these vital transport links on which citizens depend for livelihoods, supplies and mobility are severed. The UK’s aging infrastructure has been referred to as an ‘asset time bomb’. There is also a concern that as climate changes, these aging bridges are increasingly going to have to withstand more extreme flood events accompanied by faster flowing water in riverine environments. These environmental factors may result in the bridge stock being more susceptible to the effects of scouring. Scour is the removal of material (usually soil) from around an object (e.g. a bridge pier) due to the action of flowing water. Scour often occurs in fast flowing river systems and in coastal environments. Scour is a complex soil-water-structure interaction process. This complexity makes the estimation of the amount of scour challenging when using empirical and semi-empirical approaches which often use only a few parameters such as: pier width; pier length; average particle size of the riverbed material; approach flow depth and velocity; critical velocity; angle of attack; pier shape and spacing. Scour being a complex process is also challenging to measure reliably in the field with some methods being suitable in some circumstances but not in others. This paper reports results of a study conducted at the University of Bristol which investigated the relative accuracy of eight scour prediction methods using some (or all) of said parameters. The influence of the measurement device used to originally measure the scour depths e.g. Ground Penetrating Radar, Fathometer, Bludworth Fathometer, Acoustic Doppler Current Profiler and Ambient bed in the field and how the accuracy within each of these sub-categories compares (for each method) to the prediction of the laboratory measurements is examined in detail in the paper. Recommendations are made for asset owners and policymakers on the relative merits of the different measurement approaches, when deploying scour monitoring systems in the field via use of a scour rating framework developed recently by the authors.