强潮河口桥墩涌潮压力试验研究

Experimental study of tidal bore-induced pressures on piers in a macro-tidal estuary

为明确强潮河口设计条件下涌潮压力特征,以嘉绍大桥工程为背景进行了涌潮压力的动态测试和分析。选取主墩围堰和施工栈桥进行现场观测,分析了涌潮压力分布及其变化的特点。利用经验模态分解法,研究了涌潮压力的时均和脉动特性,建立了涌潮压力及其脉动分量极值与涌潮高度的拟合关系。研究结果表明:涌潮压力变化脉动性强,经验模态分解法能较好地处理这种非平稳时变信号;时均分量反映了局部水位的平均变化趋势,脉动分量反映了涌潮与结构物相互作用时自由水面的紊动情况;从垂向分布上看,压力极值在潮前低水位附近最大,并随着传感器安装高程的增加而减小;从平面分布上看,主墩围堰的迎潮面压力极值最大,背潮面最小;涌潮压力及其脉动分量的极值与涌潮高度满足指数分布规律。

To understand the characteristics of tidal bore-induced pressures on design condition in a macro-tidal estuary,the Jiashao Bridge on the Qiantang River was cited as an example and a dynamic test in site during the construction of the bridge was performed.The tidal bore-induced pressures on main pier cofferdam and construction trestle were measured,and the features of distribution and the change of the pressures were analyzed. The time-averaged and fluctuating pressures due to the tidal bore were discussed by the Empirical Mode Decomposition（ EMD） method. A fitting relationship between the pressures extrenmum and the height of the tidal bore was developed. The measured pressures possess the characteristics of strong fluctuation and the EMD method can effectively deal with the non-stationary and time-varying signals. The time-averaged components reflected the mean change trend of the local water level and the fluctuating components reflected the turbulence of the free surface on the interaction between the tidal bore and the structures. For the vertical distribution,the location of the maximum pressure extremum was on the vicinity of the low water level and the values decreased with the increase of the sensor installation level. For the plane distribution,the location of the maximum pressure extremum was on the upstream face of the main pier cofferdam and the minimum value was on the downstream face. The relationship between the total pressure extremum and the height of tidal bore agreed with exponential distribution law and the fluctuating components as well.