不同近岸河床组成情况下岸坡崩塌试验

Experimental of the influence of different near-bank riverbed compositions on bank failure

  • 摘要: 在弯道水槽中开展6组试验,分别用非黏性土及黏性土填筑河床,研究相同水力作用下近岸河床组成对黏性岸坡崩塌的影响规律。研究发现,在试验给定的岸坡及河床组成情况下,非黏性河床凹冲凸淤且总体表现为淤积,近岸河床及凹岸岸坡冲刷强度大,凸岸附近床面上泥沙掺混较明显;黏性河床及凹岸岸坡均被冲刷,河床主流区冲刷强度比近岸河床及凹岸岸坡大。相较于黏性河床,非黏性河床近凹岸处较易冲刷,水流结构重新调整,凹岸坡脚处水流流速及紊动能可增至2倍左右,环流强度可增至11倍,加速了岸坡崩塌及崩塌体的分解输移;非黏性河床近凹岸坡脚处变形以及凹岸岸坡崩塌量均相对较大,岸坡崩塌强度为河床淤积强度的2~4倍,崩塌物质可充分补给河床的泥沙来源;经水力冲刷后非黏性河床组成情况下形成的河道滩槽高差相对较小,河道横断面相对宽浅。

     

    Abstract: Six sets of experiments were carried out in a bend flume to study the impact of the cohesion of channel bed on the failure of cohesive banks. For comparison, the flume bed was consisted of cohesive and non-cohesive sediment, respectively. Results showed that, for channel bend with non-cohesive bed, the outer bank of the bend was eroded while a mixture of collapsed bank material was deposited near the inner bank. Net aggradation occurred at the channel bed. For channel bend with cohesive bed, both the channel bed and the outer bank were eroded. Degradation at the main flow area of the channel bed was greater than that near the outer bank. The bank toe of the outer bank of the bend with non-cohesive bed was more prone to be scoured than that of the bend with cohesive bed. Due to the adjustment of the flow structure near the outer bank of the bend, the turbulence kinetic energy of the flow can double and the circulation intensity can rise to as great as eleven times of its initial value, thus aggravating bank erosion and collapse and accelerating the transport of wasted sediment. Severe erosion occurred at the bank toe of the channel with non-cohesive bed, and the volume of collapsed bank material was two to four times of that aggravated at the bed. The wasted bank material contributed as sediment source for the riverbed. The height difference between the channel bed and the floodplain of the channel with non-cohesive bed was relatively smaller and the cross section was wider and shallower after scouring. This paper represents a preliminary study on the influence of the riverbed compositions on the channel erosion and bank failure. The results may help to guide bank protection and regulation of fluvial rivers.

     

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