Stochastic modelling of the extreme flow impulses leading to bridge pier scour

One of the main causes of destabilizing bridge piers has been identified as the process of scour due to the action of the turbulent flows around them, rendering it as one of the most frequent and costly infrastructure failure events all around the world. The challenge of scour-induced catastrophes will keep increasing, affecting the resilience of our society, as extreme weather intensifies affecting the exposed hydraulic infrastructure, such as bridge piers, abutments and spur dikes [1], and aquatic vegetation [2, 3]. Therefore, research into the highly dynamic scour processes that surround hydraulic infrastructure is becoming increasingly valuable. Researchers have investigated maximum scour depth estimation extensively over the past few decades, combining mean flow parameters, bridge pier, and riverbed materials characteristics using phenomenological or empirical methodologies. The precise cause of the formation and amplification of scour-holes that result in bridge pier failure are yet unknown. This study's main goal is to offer new insights on the dynamical interactions of flow structures shed downstream model bridge piers with bed surface particles, that are strong enough to remove them, thus causing the formation of scour holes. This study specifically intends to better understand the interactions between the coarse bed surface particles and the energetic events of the turbulent flow field, as modified by a cylindrical bridge pier. Extreme impulses (flow impulses above a critical impulse level [4]), are modelled using appropriately fitted probability density functions in order to generate new scour depth predictive equations. The tests are carried out in a research flume that circulates water under the same flow conditions using model bridge piers of various model pier diameters. High-resolution acoustic Doppler velocimetry is used to gather flow velocity profiles downstream of the bridge pier. The patterns of flow structures will change as the morphology of the riverbed next to a pier changes. Based on the velocity profiles captured by ADV, the study presents the variation in flow structures, including velocity (U), turbulence intensity, and turbulent kinetic energy (TKE), downstream of the four bridge pier diameters used in the experiments.

 

References

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• 2. Yagci O., Celik, F., Kitsikoudis, V., Ozgur Kirca, V.S., Hodoglu, C., Valyrakis, M., Duran, Z., Kaya S. (2016). Scour patterns around individual vegetation elements, Advances in Water Resources, 97, pp.251-265, DOI: 10.1016/j.advwatres.2016.10.002.
• 3. Xu, Y., Valyrakis, M., Gilja, G., Michalis, P., Yagci, O., Przyborowski, L. (2022). Assessing riverbed surface destabilization risk downstream isolated vegetation elements, Water, 14(18):2880. DOI: 10.3390/w14182880.
• 4. Valyrakis, M., Diplas, P., Dancey C.L. (2011). Entrainment of coarse grains in turbulent flows: an extreme value theory approach, Water Resources Research, 47(9), W09512, pp.1-17, DOI:10.1029/2010WR010236.