Bridge scour : climate change effects and modelling uncertainties.
Creators: name: Ekuje, Friday T.
Publisher: name: University of Surrey
Year: 2020

description: Scour of bridge piers and abutments has been identified as the main cause of bridge collapse around the world. Undermining of bridge foundations occurs by river sediment removal which may lead to loss of their load bearing capacity. Long-term climate change arising from global warming has the potential to further exacerbate bridge scour due to increased river flooding resulting from increased precipitation. It is important for bridge owners and managers to understand how the risk of their bridge is likely to change due to the potential effects of climate change as this will assist towards their long-term management so that the consequences arising from bridge failures/damage can be minimised as far as possible. In the UK, climate change is expected to increase the magnitude and/or frequency of precipitation, leading to increased and/or more frequent river flooding. Several recent studies on high river flows in various British rivers predict future peak discharges that capture climate change effects. These predictions supersede the older 20% and 25% allowances that have been used in the UK in the past for climate change analyses. In this research, selected climate change allowances for the UK (Environment Agency, 2016) were applied to two common bridge assessment methodologies. As part of this study, the UK highway and railway scour assessment codes were reviewed to assess their capability in capturing climate change effects on bridge scour and identify potential limitations. The main limitation of the railway code was identified as being its inability to account for changes in river discharge. The Highway Agency (2012) (BD97/12), which has been developed more recently, was suitable for adaptation to capture climate change effects on bridge scour and, as a result, has been the focus of this study. A large number of analyses were carried out as part of this study to quantify the effects of climate change on bridge scour. The generated scour data consisted of 27,000 scour depths for bridges on wide river channels, 18,000 on intermediate and 9,000 on narrow channels, each accounting for different median sediment sizes, foundation depth, pier width and angle of attack. The aim was to simulate a large number of scenarios of bridge-river configurations to identify which situations are more susceptible to climate change effects. It was found that, in some situations, climate change has the potential of shifting the scour risk ranking of bridges to a higher risk level, potentially leading to changes in their long-term risk management. The angle of attack effect on scour risk was found to be the factor that has the most significant effect on scour risk irrespective of bridge location/river channel type. Other key findings of this research are that Highway Agency (2012) the BD97/12, the scour assessment method for highway bridges over predicted scour depth. Sediment sizes and foundation depths have significant effect on bridge scour alongside the opening ratio of a bridge The availability of a large database with scour field measurements in the USA offered the opportunity to assess the accuracy of the scour model predictions in the Highway Agency (2012) BD97/12. The majority of bridge scour equations have been derived from idealised laboratory studies which may not necessarily be representative of realistic river conditions. Statistical analyses were used to quantify the deviations between code predictions and real measurements. The former were found to lead to conservative predictions. Probabilistic distributions were fitted to the data and suggested as modelling uncertainty factors to be used with the existing scour models in the codes to update their predictions to more realistic levels.