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Temporal evolution of scour at bridge abutments in compound channels

International Journal of Sediment Research 2022年第5期37卷 662-674页

作者： Yifan Yang Bruce W.Melville Xiaozhou Xiong Lu Wang School of Engineering The University of Waikato Risland New Zealand Department of Civil and Environmental Engineering The University of Auckland State Key Laboratory of Hydraulics and Mountain River Engineering College of Water Resource and Hydropower Sichuan University

Bridge abutment-induced sediment scour in compound river channels is time-sensitive during floods, and, thus, estimating the scour rate has significance in design. In the current study, large-scale laboratory experiments were done to examine the influence of multiple factors on scour evolution,including channel geometry, bed mobility(clear-water or live-bed), and lateral(embankment intrusion) and vertical(deck submergence) flow contractions. A new method is applied for scour measurement and determination of characteristic scour trends. Results show that the nondimensional time scale is related to flow intensity and may peak before reaching the clear-water scour threshold; the corresponding equations also are derived. It is found that the use of scour countermeasures has a significant impact on the scour rate, and the existing equations for unprotected abutments have limitations. Under clear-water conditions, the scour rate is closely related to the overall flow contraction, which can be better reflected by the ratio of the approaching unit discharge to that at the bridge section. Specifically, the effect of vertical flow contraction on scour rate is more dominant than other factors. Two scour rate curves are derived to suit different structural and flow contraction types for clear-water scour. In contrast, the live-bed scour rate data are generally consistent and fall in a narrow band, showing less dependence on other factors. Finally, a new design approach is established to estimate the time scale and scour rate using the new equations proposed in this paper.

关键词： abutment scour Temporal evolution Compound channel Time scale scour rate

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scour and scour Countermeasures at Bridge Sites

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Transactions of Tianjin University 2008年第4期14卷 289-295页

作者： CHIEW Yee-Meng School of Civil and Environmental Engineering Nanyang Technological University

This paper examines scour and scour countermeasures at bridge piers and abutments. abutment scour is by far more complex than its counterpart associated with piers because of the possibility of the presence of a floodplain. Notwithstanding this, the mechanism of scour at both piers and abutments is very similar; moreover, the failure mechanisms associated with both armoring and flow-altering countermeasures are not very different. In rivers with a floodplain, abutment scour becomes much more complex. In cases where the abutment ends at or near to the floodplain, it can initiate bank erosion, which clearly is an important erosion problem that is quite distinct from the customary scour at either an abutment in rivers without a floodplain or a pier. For this reason, abutment scour can be very site-specific while pier-scour is more generic in nature. To this end, the ability to identify the type of abutment scour that may form in a particular channel is closely related to an engineer's ability to propose devices for effective scour *** summarizing research efforts on using riprap as a pier or abutment countermeasure over the past few decades, this paper highlights the deficiencies of riprap in arresting pier scour. To this end, different failure mechanisms are identified. They are shear failure, winnowing failure, edge failure, bedform-induced failure and bed-degradation induced failure. Each failure mechanism can singly or, more likely, combine to cause the eventual breakdown of the riprap layer. The study shows that a riprap layer is vulnerable to other failure mechanisms even though it is adequately designed against shear failure, rendering it ineffective in arresting scour.

关键词： abutment scour pier scour river engineering scour countermeasure riprap protection sediment transport

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