中文摘要：

在应用有限差分FLAC3D软件对黄土高原小流域概化模型塑性屈服区分布规律进行数值模拟的基础上,采用基于FLAC3D的有限元强度折减法和简化一次二阶矩法相结合的方法研究了小流域概化模型重力侵蚀稳定可靠度和破坏概率。结果表明：小流域剪切塑性区域主要分布于坡面和沟坡大部分区域,张拉塑性区域主要分布于梁峁顶和梁峁坡上部;小流域边坡整体破坏概率达到28.6%,高于1%,表明流域重力侵蚀处于高破坏概率范畴之内,处于不可接受的风险水平,需采取适当的工程措施以提高其稳定性;采用安全系数法和可靠度相结合的二元指标评价体系分析和评价边坡稳定性,能获得更为合理、可靠的分析结果。相关数值模拟和稳定可靠度分析结果可应用于流域重力侵蚀研究中,为推动流域侵蚀产沙时空规律研究的深入发展和小流域水土流失综合治理提供科学依据。

英文摘要：

Gravity erosion is an important agent for soilerosion and accounts for heavy portion of the total soil-ero- sion amount in the Loess Plateau, and is one of main sources of the formation and maintenance of hyper-concentrated flow in the middle reaches of the Yellow River, thus the study on gravity erosion has great theoretical and application values. The finite difference software, i.e. FLAC3D, is used to simulate the distribution law of plastic yield zone of a small watershed model in the paper, and the systematic method of combining strength reduction method based on FLAC3D with simplified first-order second-moment method is applied to study the stability reliability and failure probability of the small watershed model. The results in the paper are as follows ： firstly, the volume of shear plastic yield zone in the watershed model accounts for about 99.5 percent of that of total plastic yield zone in the watershed, while that of tension plastic yield zone accounts for only 0.5 percent, which reveals that shear plastic yield mainly leads to the failure of the slopes of the small watershed; secondly, from a view of the distribution of plastic yield zone applied to the Mohr -Coulomb yield criterion, the shear plastic zone is mainly distributed in the most area of slope and gully slope, while the tension plastic zone is mainly distributed on the top and slopes of barren hills; thirdly, according to the calculation results on simplified first-order second-moment method, the total failure probability of the small watershed model is up to 28.6 percent, i.e. much higher than 1.0 percent, which reveals that the small watershed is in non-acceptable risk level, as a result, some proper engineering measures should be taken to improve its stability; finally, more reasonable and reliable analysis results on slope stability of watershed could be obtained, throughout the application of the binary index evaluation system of combining traditional safety factor method and reliability analysis method. The numerical simulation res