下游设有防护坝的浅基桥梁局部冲刷研究

Research on the local scouring of shallow foundation bridge with downstream guard dam

针对桥梁下游设置防护坝后桥墩局部冲刷特点,通过水槽单体模型60多个组次的局部冲刷试验研究,分析了桥墩局部冲刷的机理和影响冲刷深度的因素。系列试验分析表明,在设有防护坝的边界条件下,桥墩局部冲刷既受来流流速、下切涡旋、桥墩形状尺寸、床沙粒径与级配的影响,同时还受防护坝距离与坝顶高程的制约。作者引入"控制底坡"反映防护坝拦沙以及对桥墩防护的影响,在理论推导与量纲分析的基础上,通过多元回归分析,推导出有拦沙坝防护的非均匀沙桥墩局部冲刷计算公式。该公式与实测数据有很好的拟合性,本文提出的最优控制底坡也为浅基桥梁防护工程设计提供了参考依据。

Based on the characteristics of local piers scouring after the guard dam buih in the downstream of the bridge, by the monomer model experiment of flume, sixty groups of local piers scouring experiments have been carried on. The principle and the influence factors of the local piers scouring have been analyzed. The results of series model experiments show that with the downstream guard dam, the local piers scouring is influenced by the approach velocity, down-shearing vortex, shape and dimensions of the piers, diameters and＇ grades of the bed sands; it is also affected by the elevation of the dam and distance between the piers and the dam. The concept of ＂control slope＂ is introduced in order to reflect the impacts of the guard dam to the piers. Based on the theoretical deduction and dimensions analysis, the equation to calculate the local scouring with no-uniform bed sands is acquired by multivariate regression analysis. The calculated value has a good agreement with the measured data, and the optimum value of ＂control slope＂ provides valuable references for bridge design of the shallow foundation with downstream guard dam.