波浪渗流力对泥沙起动的影响

Effect of wave-induced seepage force on incipient sediment motion

海岸泥沙起动的力学机理十分复杂。首先理论分析了波浪作用下床面泥沙颗粒所受的主要作用力,然后将上举力和有效重力分别与渗流力进行比较分析。计算结果表明渗流力随着波高的变化其方向也发生向上或向下的变化,渗流力与上举力和有效重力之间存在着相位差,不同粒径的泥沙在一个周期内均有一时段渗流力远大于上举力;对于渗透系数小的细颗粒泥沙,渗流力远大于泥沙颗粒的上举力和有效重力。进一步通过水槽试验分析了不同波浪参数作用下孔隙水压力梯度对泥沙起动的影响,试验结果表明波浪渗流力对海床细颗粒泥沙的起动有着重要作用,特别是在分析长周期波浪作用下细颗粒泥沙起动规律时,需考虑波浪引起的渗流力影响。

The mechanism of incipient motion of sediment transport can be very complicated.In this study,the major wave-induced forces acting on sand particles on sea beds are discussed;and a comparison is made between the seepage forces and the uplift and effective weight forces.An experimental study is conducted in a flume to investigate the effect of wave-induced porewater pressure gradients on incipient sediment motion.The result shows the direction of seepage forces varies with wave height changes.There exist phase differences between the seepage forces and the uplift and effective weight forces.For different sand particles,there exist certain time periods during which the seepage force can be much larger than the uplift force.For fine sediment deposition with low permeability coefficient values,the seepage force can always be much larger than the uplift and effective weight forces.The experimental results show that the wave-induced seepage force plays an important role on the incipient motion of fine sediment.The wave-induced seepage force should be properly considered when analyzing the incipient motion of fine sediment especially under the influence of long nonlinear waves.