Scour around bridge pier near a bank and its influence on flow pattern

岸边桥墩附近的局部冲刷主要是由岸边三维水流(垂直流)和并排螺旋流引起的，此外还有马蹄涡和绕自由墩的强迫下流，以及河床退化和水流集中等原因。并排螺旋流是由内衬点源喷出的气泡在床层纵向和横向上的作用而人为形成的。在验证了该流态与河道现有流态接近后，研究了桥墩周围水流干扰以及竖墙的存在对流态变形的影响。结果表明，桥墩在并排螺旋流中的位置对桥墩周围的局部冲刷深度和冲刷面积有显著影响。从实用角度看，在并排螺旋流中，桥墩局部位置的冲刷深度增加了近20%。在垂直井壁附近，并排螺旋流动被强迫保持稳定，除了井底区域外，沿井底上升的流动促进了近井螺旋运动的强度。因此，在距墙体适当距离的桥墩周围，冲刷深度可以达到最大。文中还介绍了复式渠道和弯道情况下，近墙桥墩局部冲刷的一些实例，但其推广还有待进一步研究。

Local scour around bridge pier near a bank, is pepecuciarly caused by 3D-flow near a bank (vertical flow) and side by side spiral flow, in addition to horse-shoe vortex and forced down flow around free pier, and also due to river bed degradation, flow concentration, etc. Main experimental results are summarised below.1. Side by side spiral flow condition was artificially formed by the effect of air bubbles ejected from lined point sources on the bed longitudinally and laterally. And after verification that this flow condition is close to the existing flow pattern in a river, tha ways of deformation of flow pattern due to the interference with the flow around bridge pier and also the existence of vertical wall were investigated.2. Local scour depth and scoured area around bridge pier are clarified to be remarkably influenced by the position of pier in the side by side spiral flow. It is considered to be significant from the practical point of view that the scouring depth increases almost 20% at some location of bridge pier in side by side spiral flow.3. Side by side spiral flow is forced to be stable near vertical wall where uprising flow along the well except the area of bottom encourages the strenght of spiral motion near the well. Therefore, scouring depth can become maximum around bridge pier installed at proper distance from the wall.4. Some examples of local scour around pier near the wall are described in the cases of compound channel or curved channel, but its generalization is a problem in future.