大坝迎水坡的最不利工况是长期蓄水（高水位运行）后水位骤降，影响此时上游坡土体稳定性的因素有水位降落速度、土体特性等。借助于渗流分析软件 Geoslope 和 unsst2 ，不仅从渗流稳定性出发，说明了坡面渗水的危害；从防止大坝上游坡在库水位下降时产生自由溢出点出发，拟合了不同k/ μ v 时库水位下降的临界高度；而且考虑了由于各种原因产生的土体各向异性和基质吸力摩擦角φ^b 对上游坝坡稳定性的影响。研究表明，对于库水位下降时上游坡稳定性分析，尤其应结合渗流场计算结果，同时考虑工程实际中各种因素的影响。

When reservoir water level drops sharply and rapidly from long  time high-level storage, the falling velocity of reservoir water level and soil property will exert adverse impact on the stability of upstream slope soil mass. The hazard of seepage on the upstream slope surface is demonstrated by seepage analysis softwares (Geoslope and unsst2). Fitted curves between k/μv and critical descent altitude of reservoir levels when flow with free surface does not appear are presented. Moreover, both the influence of soil anisotropy caused by various factors and the impact of substrate suction internal frictional angleφ^b on the stability of upstream slope seepage are also considered. The study reveals that all possible factors in practical projects and the results of seepage field calculation should be considered in the analysis of the seepage stability of upstream slope during the drawdown of reservoir level.