荆江段抛石护岸稳定性计算及其影响因素分析

Calculations of bank stability of riprap revetment in Jingjiang reach and analysis of its influencing factors

针对长江中游荆江段已护岸段的工程水毁问题,本文考虑单个块石起动及整体滑移破坏两种水毁模式,提出了基于力学过程的抛石护岸工程稳定性计算模型。以荆江北门口河段的两个典型断面为例,采用该模型计算了2017年8月—2018年10月水下抛石护岸工程的水毁破坏过程,定量分析了近岸流速、床面冲淤幅度、块石粒径及水下岸坡坡度对抛石护岸坍塌比的影响。结果表明:计算时段内抛石护岸工程总体上处于较稳定的状态,坍塌比均值仅为5%;坍塌比随近岸流速的增加而增加,当平均流速超过一定临界值时,坍塌比急剧增加,且块石团休止角越大,该临界值越大;坍塌比也随河床冲刷深度的增大而增大,且同样在特定冲刷深度下会出现急剧增加的变化趋势;随着块石粒径的增加和水下自然坡度变缓,抛石的坍塌比逐渐减小,且水下坡度缓于1:2.0的抛石护岸工程稳定性较高。

A bank stability analysis model of underwater riprap revetment is presented that has been adopted to calculate the riprap failure processes at two typical cross sections of Beimenkou in the lower Jingjiang from 08/2017 to 10/2018.The impacts of different factors on revetment collapse are examined,including near-bank velocity,bed erosion and deposition,riprap-rock size,and bank slope.The calculations show that in this period,generally the riprap revetment was relatively stable with an average collapse ratio as low as about 5%.This ratio grew as flow velocity increased,and its growth became sharp at a certain critical velocity value that was higher in the condition of riprap with a larger angle of repose.A similar variation trend also showed between the collapse ratio and bed scour depth.With the increasing riprap-rock size or the decreasing underwater slope,the collapse ratio decreased gradually.Generally,riprap revetment with an underwater slope lower than 1:2.0 showed better stability.