波流共同作用下正斜桩局部冲刷试验研究

Experimental Study of Local Scour Around an Downstream Inclined Pile Under Combined Waves and Current

随着海洋资源大规模开发和利用,斜桩基础凭借良好的水平承载力特性在跨海大桥、海上平台、高桩码头等海洋结构物中得到了广泛应用。在波流强烈的非线性作用下,斜桩附近会发生严重的局部冲刷,降低结构物的安全性,甚至会导致破坏。为了解不同波高、流速条件下,倾斜角度对正斜桩冲刷特性的影响,并对比与垂直桩冲刷特性的差异,在波流水槽中开展波流共同作用和纯流作用下的局部冲刷试验。通过对α=0°、10°、20°、30°的正斜桩进行试验,研究了倾斜角度对冲刷历时、相对时间尺度及冲刷坑形态的影响,开展了无量纲参数Fr、KC、U_(cw)对正斜桩最大冲刷深度的影响分析,并与前人的垂直桩数据进行详细对比。结果表明:当桩向下游倾斜时,倾斜角度对于波流共同作用下斜桩冲刷特性有着重要的影响。与垂直桩相比,随着倾斜角度的增加,正斜桩冲刷深度发展速率、冲刷坑尺度及深度逐渐减小,相对时间尺度逐渐增大;对于20°正斜桩,当d_(50)=0.403 mm,U_(c)=0.206 m/s,H=7 cm时,最大冲刷深度点由侧前方转移至正前方的时间约为60 min,远大于垂直桩。正斜桩沙丘沿中轴线对称分布,呈双峰结构,且冲刷坑形态与垂直桩明显不同;动床条件下,床面形成规则的沙波,冲刷坑尺度进一步减小,双峰更加明显。正斜桩相对冲刷深度为无量纲参数Fr、KC、U_(cw)的函数,与垂直桩拟合曲线的趋势保持一致。

With the rise of development and utilization of marine resources,inclined pile foundation with good horizontal bearing capacity has been widely used as marine structures such as cross-sea bridge,offshore platform and high pile wharf.Under the action of strong nonlinear superposition of wave and current,severe local scour will occur around the inclined pile,which will reduce the safety of the structure and even lead to structural damage.In order to understand the influence of inclination angle on the scour characteristics of downstream inclined piles under different wave heights and flow velocities,and the difference from that of vertical piles,local scour tests under combined waves and current and pure current were carried out in the wave-current flume.By conducting tests onα=0°,10°,20°and 30°downstream inclined piles,the influence of inclination angle on scour duration,relative time scale and scour hole morphology was studied.The influence of dimensionless parameters Fr,KC and U_(cw) on maximum scour depth of downstream inclined pile was analyzed,and detailed comparison was made with previous vertical pile data.The results showed that when the pile was inclined to downstream,inclination angle had an important influence on the scouring characteristics of pile under combined waves and current.Compared with the vertical pile,with the increase of inclination angle,development rate of scour depth,scale and depth of scour hole gradually decreased,while ralative time scale increased gradually.For the 20°downstream inclined pile,when d_(50)=0.403 mm,U_(c)=0.206 m/s,H=7 cm,the time for maximum scour depth point to be transferred from lateral front to front was about 60 min,which was much longer than that of a vertical pile.The dune of downstream inclined pile was distributed symmetrically along the central axis and had a bimodal structure,and the scour hole shape was obviously different from that of a vertical pile.Under the condition of moveable bed,regular sand waves were formed on the bed surface,the scour hole scale was further reduced,and the double peaks were more obvious.The relative scour depth of downstream inclined pile was the function of dimensionless parameters Fr,KC and U_(cw),which was consistent with the trend for a vertical pile’s fitting curve.