Local pier scour has been recognized as one of the most significant causes of bridge failures. Despite numerous studies on the subject of local pier scour have been conducted, there remain problems in accurate scour prediction because almost of the past studies have focused only on scour depth around simple shape of a bridge pier with or without considering their time development, even though prototype bridges usually have complex pier configurations. Thus, the objective of this study is investigation of the scour process around complex shape of pier including various shape of foundations and columns other than cylindrical shape over time for the purpose of understanding the relationships between hydraulic variables and resulting time development of scour. In this study, two field sites in Georgia, USA were selected, and corresponding scale-down bridge models and river geometries were fabricated in a hydraulic laboratory to address objectives of this study. Three different sizes of sediment and several geometric scales of bridge pier models were used to investigate the effect of relative sediment size, which is defined as the ratio of the pier width to the median sediment size. Through the visualization experiment, it is observed that exposure of complex shape of pier footing has important role for the temporal variations of scour depth over time. In addition to the quantitative visualization analysis, based on the experimental results, scouring rate formulas are suggested with the help of dimensionless, effective flow work concept according to the value of the relative sediment size. Findings in this research can be used to improve scour prediction methods that currently tend to overpredict bridge scour depth.

当地的桥墩冲刷已被认为是桥梁故障的最重要原因之一。尽管已经进行了许多有关当地墩冲刷的研究，但是准确的冲刷预测仍然存在问题，因为几乎所有的过去研究都集中在围绕桥墩简单形状的冲刷深度上，而不论是否考虑其时间发展，尽管原型桥梁通常具有复杂的桥墩配置。因此，本研究的目的是随着时间的推移研究围绕复杂形状的墩的冲刷过程，包括复杂的基础形状和圆柱形状，而不是圆柱形状，以了解水力变量与冲刷时间发展之间的关系。在这项研究中，选择了美国佐治亚州的两个野外地点，并在水力实验室中制作了相应的按比例缩小的桥梁模型和河流几何形状，以解决本研究的目标。三种不同的沉积物尺寸和几种桥墩模型的几何比例被用来研究相对沉积物尺寸的影响，其定义为桥墩宽度与中值沉积物尺寸的比率。通过可视化实验，观察到墩脚形状复杂的暴露对于冲刷深度随时间的变化具有重要作用。除了定量可视化分析外，还基于实验结果，根据相对沉积物尺寸的值，借助无量纲，有效的流功概念，提出了冲刷率公式。