Investigation of the total scour at river bridges under pressurized flow condition

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Thesis Type: Postgraduate

Institution Of The Thesis: Gazi University, Fen Bilimleri Enstitüsü, Turkey

Approval Date: 2022

Thesis Language: Turkish

Student: Zayd Onur BARAKAT

Supervisor: Müsteyde Baduna Koçyiğit

Open Archive Collection: AVESIS Open Access Collection

Abstract:

River bridges are very important engineering structures in the transportation system. In case of pressurized flow condition that may occur as a result of increase in the river flow during flooding, excessive scouring around bridge piers may occur leading to the collapse or severe damage of the bridges with the increase in scour depth. Within the scope of this research, types of scour around bridge piers and shape of the scour hole under partially and fully pressurized flow conditions were investigated with varying approach flow depths and discharges. In the study, three experimental series in which only vertical contraction scour under pressurized flow, only local scour in free flow, and pressurized bridge scour which involves both contraction and local scour were conducted. Thus, using the experiments carried out under same conditions, the accuracy of the approach in which the pressurized flow scour depth is determined by evaluating the contraction and local scour depths separately and then adding these up to determine the total scour depth was examined.  When the scour hole profiles obtained from the contraction and local scour depths were compared with the measured pressurized flow scour hole profiles, it was observed that there is no significant difference for the pressurized flow in the transverse direction, while the difference between the two profiles increased for weir type of flow. Similarly, it was observed that there were differences in the longitudinal scour hole profiles for weir flow in the downstream of the pier. In the study, the accuracy of the empirical equations in the literature for various scour types were assessed with the help of statistical parameters and an empirical relation was proposed for pressurized flow scour. The study showed that the flow-pier interaction became more complex with the effect of increasing turbulence in case of pressurized flow condition, and the depth of the scour hole was observed to be larger when compared with the predictions of the relations in the literature.

Key Words : River Bridge, Pressure flow, Maximum scour hole depth, Sediment transport, Clear water scour, Local scour