三峡水库蓄水后，上荆江河段来沙急剧减少，河床冲刷下切，局部河段崩岸现象时有发生，影响两岸堤防安全。通常认为水流冲积作用是崩岸的主要控制因素，但已有研究表明，河道内水位变化能改变河岸土体的力学特性及受力条件，进而对崩岸过程产生较大影响。本文将一维非稳定渗流计算及黏性土河岸稳定性计算结合，构建了考虑潜水位变化的岸坡稳定性分析模型，用于计算河道内水位变化时岸坡稳定程度的调整过程。以上荆江河段荆34、公2断面为研究对象，采用该模型计算了2009年实测河道水位过程下相应断面的岸坡稳定安全系数Fs。结果表明：涨水期河岸稳定性较高，洪峰期有所降低，退水期更低；荆34、公2断面最小Fs值分别为0.83、1.39，均发生在退水期，表明前者在该时期会发生崩岸，后者较为稳定，这与实测资料相符。此外还计算了不同河道内水位变化速率下Fs值的变化过程，结果表明：岸坡稳定性在涨水速率增加时增大，在退水速率增加时则减小。因此近期上荆江河段崩岸加剧一定程度上与三峡工程运用后退水过程加快有关。%Due to the operation of the Three Gorges Project (TGP), the sediment load entering the Upper Jingjiang Reach (UJR) has been reduced greatly, and then the continuous channel degradation and signifi⁃cant bank retreat processes have occurred at local sites of this reach,which may influence the safety of flood control engineering seriously. Fluvial erosion is regarded as the dominant factor in controlling the bank retreat progress;however,existing studies indicate that the variation of in-channel water levels can af⁃fect riverbank stability greatly by changing hydrostatic confining force and influencing seepage progress. To investigate the adjustment of riverbank stability corresponding to the variation of in-channel water level, the adopted approach here is to couple the module of riverbank stability analysis with the module of one-di⁃mensional unsteady seepage simulation. Taking the typical sections of Jing34 and Gong2 in the UJR as the study sections, and the proposed approach was used to simulate the temporary change of riverbank stability degrees during the 2009 hydrological year. Model predictions indicate that the riverbank should be stable during the rising stage, and would become less stable during the flood peak and recession stages, and es⁃pecially in the recession stage, bank retreat is predicted to occur with high probabilities. However, during the flood peak stage, the rapid decrease of in-channel water levels might cause riverbank stability to re⁃duce rapidly in a short period. At the recession stage, the calculated minimum safety factors of riverbank are 0.83 and 1.39 at Jing34 and Gong2 respectively, which indicates the bank at Jing34 would collapse during this stage. In addition,the effects of different rising and recession rates of the in-channel water lev⁃els on the degree of bank stability have also been investigated. The results show that the degree of river⁃bank stability increases with a rising rate of water level,but it reduces when the in-channel water level de⁃creases more rapidly.
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