渗流作用下的岸坡泥沙起动条件

考虑渗透力作用,分析坡面泥沙受力特点,推导出岸坡均匀沙的起动条件和临界切应力计算公式,并采用不同渗流比降和不同水流方向的算例,以及长江中下游典型岸坡的实例,对渗流作用作出了定量分析。结果表明,泥沙起动流速曲线存在明显的转折点,可以解释崩岸的突发性;向坡外的渗流将大幅降低岸坡泥沙起动条件;冲刷水流方向也影响泥沙起动流速,在接近零流速破坏坡角时影响显著。

Incipient motion of riverbank sand subject to seepage

Incipient motion criteria and a dimensionless critical shear stress for uniform sand particles on riverbank slopes were derived by analyzing the focces, including seepage acting on the particles. The hydraulic gradients and flow directions were varied in tests to investigate the effects of the seepage on the incipient motion of the sand. The seepage analysis was applied to the double soil layers typical of the middle and lower reaches of the Yangtse River to compute the distribution of the dimensionless critical shear stress along these slopes. The results show that the curve of the threshold flow velocity with respect to slope angle has an obvious turning point, which may explain why riverbanks usually collapse suddenly with outward seepage in the bank significantly reducing the threshold velocity. The flow direction also significantly affects the threshold velocity when the slope angle is very close to the critical angle at which the sand will start moving without the effect of flow.