A review of floodwater impacts on the stability of transportation embankments

Infrastructure embankment failures due to flooding have been recorded in many countries. The consequences of flood-induced embankment failures have mainly been limited to infrastructure downtime; however, failures have caused fatalities and include multiple near-miss events. Here we review the types of flood which cause transportation embankment failure and the associated types of failure, processes which cause failure, and the potential for lasting slope weakening after flooding. Four types of flood which cause transport embankment failure are identified; offset head, overtopping, basal floods at slope toes and floods above slopes. Failure is caused by flood-specific processes including rapid drawdown, sliding, scour and internal erosion in addition to the development of destabilisation from effective normal stress decrease and saturation loading. Existing destabilisation modelling tends to focus on single flood events which cause failure, with limited consideration of repeat flooding and the long-term degradation of embankment strength which may occur following rainfall and flooding. Although there is a well-developed understanding of generic landslide development, we suggest that that there has been limited consideration of the destabilising effects caused by dynamic conditions which develop during repeat flooding. Furthermore, while the effects of live traffic loading from high speed trains during flooding have previously been considered and shown to cause destabilisation, such previous work is found to be limited to specific embankment structures which are not representative of the wider rail network and considerable uncertainty exists for older earthworks. We conclude this review by identifying future research priorities to help improve prediction and mitigation of flood-induced embankment instability.