河床溯源冲刷影响下的桥墩冲刷

主要针对河床采沙所致的溯源冲刷对水下结构物周围冲刷影响的问题,研究冲刷演变及预测方法,为结构物安全防洪提供参考。通过水槽试验观测了床面突降条件下的溯源冲刷和墩柱局部冲刷耦合发展规律及其主要影响因素,建立了溯源与局部耦合冲刷的实时计算方法。溯源冲刷耦合下的局部冲刷与平床时的冲刷之比呈上凸曲线变化,与距离、流量及跌水水头差有关;局部冲刷和溯源冲刷对总冲刷深度的贡献比是墩柱与采沙坑距离、跌水水头差及流量的函数;在河床采沙的一定影响范围内,溯源冲刷到达时的瞬间冲刷速率远大于局部冲刷速率。本文的计算方法,可用于预测溯源与局部耦合冲刷时结构物总冲刷深度的发展。

Pier scour under influence of headcut erosion of sand pit

Considering the influence of retrogressive erosion on total scour at underwater structure, the study of scour evolution and prediction was conducted to provide a reference to the flood protection of struc-ture. Based on the flume experiments,the evolution and influential factors of retrogressive and local scour were observed. In addition,a time-dependent calculation method was proposed for the coupling scour. The ratio of local scour with or without retrogressive erosion varies with the distance between the pier and sand pit in an up-convex shape curve,of which increase or decrease is related to the flow discharge and hy-draulic drop at the pit. Furthermore,the contribution ratio of local scour and retrogressive scour to the to-tal scour depend on distance between pier and sandpit,hydraulic drop and discharge. In a featured loca-tion,the rate of retrogressive erosion is instantly times larger than that of the local scour at pier. The cou-pling calculation method proposed in this paper is capable to predict the total scour depth at a pier includ-ing retrogressive erosion and local scour.