长江口沙波分布区桥墩局部冲刷深度计算公式的改进

New formula of local scour depth of the near-shore sand waves covered areas:Sutong Bridge

利用多波束水深仪、浅地层剖面仪和多普勒流速仪对长江口苏通大桥南、北主墩区域现场测量,结果显示主墩周围最大冲刷深度为8.3 m和19.6 m。建墩前后河床形态变化显著,建墩后桥墩所在床面由平床改变为典型不对称沙波发育,平均波长为30.8 m和23.1 m,平均波高为4.2 m和9.4 m,陡坡朝向下游。基于实测水文条件和地形资料,以沙波起动流速和落急最大流速分别取代单向流作用下"平床"假定的桥墩局部冲刷计算公式中单颗粒泥沙的起动流速和墩前流速,获得河口涨落潮双向流作用下沙波底床桥墩局部冲刷计算公式。且该公式计算的苏通大桥南、北主墩局部冲刷深度为9.5 m和22.1 m,非常接近实测值。

Measurements were made in the area around the south and north piers of Sutong bridge in the Yangtze River estuary using multi-beam sonar,sub-bottom profiler and Doppler flow meter.The results showed that the maximum local scour depths were 8.3 m and 19.6 m.Meanwhile the bed configuration changed significantly after the Sutong Bridge construction,from an originally flat bed to a dune-covered bed.The mean wave lengths were 30.8 m and 23.1 m,the mean wave height were 4.2 m and 9.4 m,and the steep slope faced towards the downstream.Furthermore,based on the collected data,we improved the piers local scour formula,by using the sand incipient velocity instead of by dunes＇ incipient velocity,and the single directional current velocity before piers instead of the maximum velocity of ebb and flow.The results showed the maximum local scour depths were 9.5 m and 22.1 m,which were close to the measurement results.Therefore,it is practicable to use the formula to estimate the local scour depth in the near-shore covered dune areas.