冰盖下桥墩局部冲刷随时间变化的试验研究

在寒冷地区，河道中冰盖的存在会改变河道流速分布。与明流条件相比，冰盖条件下水流最大流速点会向河床移动，加剧桥墩周围的局部冲刷。过度的局部冲刷会导致桥梁倒塌。基于水槽清水冲刷试验，对冰盖与明流条件下圆柱型桥墩局部冲刷随时间的变化进行了研究，试验结果表明：冰盖下桥墩局部冲刷速率大于明流。平衡冲刷深度比明流条件下的约大12%，且冲刷平衡所需时间比明流条件下的要约大10%。分析了水流强度与无量纲冲刷深度的关系以及冰盖与明流条件下冲刷深度变化速率的差异，给出了冰盖下局部冲刷深度随时间变化的经验方程，研究成果可供实际工程参考。

Time-dependent local scour around bridge piers under ice cover-an experimental study

In cold regions, the presence of ice cover in a river changes the flow velocity distribution. The maximum flow velocity under an ice-covered flow condition is shifted closer to the channel bed,which can intensify the local scour process around bridge piers comparing to that under an open flow condition. Excessive scour around bridge piers may cause a collapse of bridges. In the present study,a series of clear-water experiments were carried out in flume to investigate the time-dependent local scour around a cylindrical pier under both ice-covered and open flow conditions. The results show that the local scour rate under ice-covered condition is faster than that under open flow condition. The equilibrium scour depth under ice-covered flow condition is 12% more than that under open flow condition. Also, the time needed for achieving an equilibrium state under ice-covered flow condition is 10% more than that under open flow condition. The relationship between the flow intensity and the dimensionless scour depth has been assessed, and the difference between scouring rates of two different cover conditions was studied. An empirical equation for calculating time-dependent local scour depth under ice-covered flow condition was developed. The results of this study can be used as reference for engineering practice.