In this experimental study, the temporal development of local scour is studied around semi-circular end bridge abutments under quasi-unsteady clear-water flow conditions in a rectangular sediment channel. A step-wise hydrograph of 6 h duration is used in the experiments. Six different abutment lengths having constant width, with uniform sand as bed material, were tested for three different successive flows – each applied continuously for 2 h. Bathymetry of the bed level was measured around the abutment every 15 min with the help of a measurement device to observe temporal development of the local scour around the semi-circular end abutment. Effects of the abutment length, flow intensity and time on the scour depths around semi-circular end bridge abutments, along with those at the front, upstream and downstream faces of the abutment, are also investigated and discussed. It is shown that the maximum scour depth always occurs at the front noses of the abutments compared with those at the upstream and downstream noses. A dimensionless empirical formula is derived to predict the scour depth at the front nose of the abutment as a function of related parameters. The results reveal that flow intensity is the most critical parameter in scour development.

中文翻译：

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准非稳态条件下半圆形端桥台面局部冲刷演化

在本实验研究中，研究了矩形沉积河道中准非稳态清水流条件下半圆形端桥台附近局部冲刷的时间发展。实验中使用了 6 小时持续时间的逐步水文曲线。六种不同长度的具有恒定宽度的基台，以均匀的沙子作为床材料，测试了三种不同的连续流动——每一种连续应用 2 小时。在测量装置的帮助下，每隔 15 分钟测量一次基台周围的床位水深，以观察半圆形端基台周围局部冲刷的时间发展。桥台长度、流量强度和时间对半圆形端桥桥台周围冲刷深度的影响，以及桥台前、上游和下游面的冲刷深度，也进行了调查和讨论。结果表明，与上游和下游前端相比，最大冲刷深度总是出现在桥台的前端。导出了一个无量纲经验公式来预测基台前鼻部的冲刷深度作为相关参数的函数。结果表明，流动强度是冲刷发展中最关键的参数。