Some observations on the prediction of bridge scour from first principles

The development and generation of scour holes around hydraulic infrastructures, such as bridge piers, can affect their stability and lead to their structural failure. Bridge scour is becoming increasingly challenging to tackle, especially under the context of climate change, increased urbanization pressures, and lack of adequate funding to inspect and maintain aging built infrastructure near water surface bodies [1,2]. As a result, many infrastructure failures are driven by the formation of scour holes due to strong enough turbulent flows. Traditionally, the research community has explored infrastructure scour by aiming to identify correlations between phenomenologically relevant parameters, such as the pier characteristics and the mean flow conditions around it. However, such bridge pier scour prediction models and relevant formulas are developed focusing on idealized lab experiments using bulk/averaged parameters. Thus, they may receive criticism due to their relatively limited generalization ability and their capacity to be validated with field data.

This study adopts a new paradigm assuming that it is rather meaningful to study scour as a dynamic process stemming from the interplay of the highly turbulent three-dimensional eddies stemming downstream of the pier with the granular material comprising the bed around it. Motivated by this observation and recent relevant research, the current study aims to shed more light on the role of impulse induced by the dynamics of flow energy acting on individual particles and setting them in motion [2], leading to the scour hole formation.

To the above goal, experimental tests are conducted in a water-recirculating flume with a depth of 50cm, a width of 90cm, and a length of 700cm. The generated scour hole developed past different cylindrical pier models is studied. Flow impulses are calculated from high resolution (200Hz) flow velocimetry data collected over a finely spaced grid downstream of the bridge pier model. This study is a first attempt to demonstrate the application of the impulse criterion towards predicting scour depth - as opposed to all past phenomenological models that employ bulk flow and pier parameters.

 

References

[1] Pandey, M., Valyrakis, M., Qi, M., Sharma, A., Lodhi, A.S. (2020). Experimental assessment and prediction of temporal scour depth around a spur dike, International Journal of Sediment Research, 36(1), pp.17-28, DOI: 10.1016/j.ijsrc.2020.03.015.

[2] Khosronejad, A., Diplas, P., Angelidis, D., Zhang, Z., Heydari, N., Sotiropoulos, F. (2020). Scour depth prediction at the base of longitudinal walls: A combined experimental, numerical, and field study, Environmental Fluid Mechanics, 20, pp.459–478, DOI: 10.1007/s10652-019-09704-x.

[3] Valyrakis, M., Diplas, P., Dancey, C.L. (2013). Entrainment of coarse particles in turbulent flows: An energy approach, Journal of Geophysical Research, 118(1), pp.42-53, DOI:10.1029/2012JF002354.