Scour around Bridge Pier under Abrupt Change of Water Pressure

据报道，到目前为止，许多桥梁严重受损，特别是在洪水或风暴期间。在这些自然条件下，水压力变化在构筑物附近发生突变，造成冲刷破坏。考虑到这种情况在水利工程领域的真实存在，本报告主要研究了在实验室通道中进行的圆形桥墩周围孔隙水压力分布、有效应力和局部冲刷发展的实验结果。结果表明：在突发性水压力变化作用下，超孔隙水压力增大导致沉积物床层液化，桥墩处局部平衡酸碱比清水稳流时明显增大；在此基础上，进一步研究了圆形桥墩周围河床材料的波浪动力特性和局部冲刷。在水波的持续作用下，桥墩周围基材的冲刷以及基材的动力稳定性是桥梁破坏的重要原因。利用实验室水槽对圆形桥墩周围清水稳流和波浪流条件下的超孔隙水压力、局部冲刷和流速分布进行了观测。结果表明，浪高越大，冲刷深度越大。在波高较高的情况下，有效应力的减小被认为是超孔隙水压力的增大。在这种情况下，桥墩周围的基材很容易被清除。

A substantial damage of a number of bridges has been reported so far especially during flood flows or storm waves. During these natural conditions, the abrupt change of water pressure variation occurs near the structures, and it causes failure due to scouring. Considering such a real occurrence in the hydraulic engineering field, this report mainly deals with the experimental results on the distribution of pore water pressure, effective stresses and local scour development around a circular bridge pier carried out in a laboratory channel under abrupt water pressure variation. The results show that the sediment bed is liquefied by an increase of excess pore water pressure under sudden water pressure variation and the equilibrium local sour increases considerably than that of clear-water steady flow at the bridge pier.Further investigations on the wave-induced dynamic behavior of bed material and local scour around a circular bridge pier were carrying out. Under persistent action by water waves, not only the scour of the bed material but also the dynamic stability of the bed material around the bridge pier is a significant reason of bridge failure. Observations were carrying out on the excess pore water pressure, local scour and velocity distributions under clear-water steady flow as well as wave flow around a circular bridge pier using a laboratory flume. The results show that the larger the wave height is, the larger the scour depth becomes. In the case of higher wave height, the decrease of the effective stress was recognized as the increase of the excess pore water pressure. In such conditions, the bed material around bridge pier is removed easily.