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

近岸桥墩局部冲刷主要是由近岸三维水流（垂向流）和平行螺旋流、马蹄涡和自由墩附近的强迫下流以及河床冲刷、水流集中等因素引起的。利用线列点源喷射气泡在床面纵向和横向的作用，人为地形成并列螺旋流条件。并在验证了该流态与河流现有流态接近的基础上，研究了桥墩周围水流的干扰以及竖壁的存在对流态的影响.研究表明，桥墩位置对并列螺旋水流中桥墩周围的局部冲刷深度和冲刷面积有显著影响。从实际应用的角度来看，在平行螺旋水流中桥墩某些部位的冲刷深度增加了近20%，这是非常有意义的.并排螺旋流在垂直壁附近被迫稳定，其中沿井沿着上升的流（底部区域除外）增强了井附近螺旋运动的强度。因此，在距墙适当距离的桥墩附近，冲刷深度最大.文中还介绍了复式河槽和弯曲河槽中近壁桥墩局部冲刷的一些实例，但其推广尚有待进一步研究。

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.