暂时性承压水导致山前缓坡破坏的模型分析

Failure Model Analysis for Piedmont Gentle Slopes Due to Temporary Confined Water

宁(南京)镇(镇江)地区大量缓倾角滑坡发生在强降雨之后,坡内水位抬升形成暂时性承压水,滑坡变形表现为坡体前缘隆起、后缘拉裂。通过对南京江宁石龙路滑坡开展现场地质调查,发现该滑坡地层结构表现为宁镇地区山前缓坡典型的上细下粗的二元地质结构特征。文章以南京石龙路滑坡破坏特征为基础,从简单的承压水分布模型与简支梁模型的基本原理出发,试图分析暂时性承压水导致坡体前缘隔水层隆起破坏的力学机制。针对滑坡前缘隆起特征,构建承压水一维稳定流模型,分析了坡体前缘透水层中承压水的分布特征;引入简支梁模型分析了承压水扬压力对隔水层的变形和稳定性的影响以及隔水层中裂隙的发育规律;确定了隔水层隆起后破坏的判据,详细分析了坡脚处扬压力水头和隔水层厚度对隔水层破坏特征的影响。研究结果表明透水层中承压水头为三角形分布,隔水层最深裂隙发育在扬压力对简支梁模型的最大弯矩处;地表隔水层最大破坏区域与坡脚处扬压力水头呈正相关,与隔水层厚度呈负相关;隔水层发生隆起—拉裂破坏时的临界扬压力水头和临界隔水层厚度近似呈线性关系。

A large number of gently inclined landslides occurred after heavy rainfall in Nanjing and Zhenjiang area.The temporary confined water was formed by the rise of water level in the slopes after rainfall.Landslide deformations showed uplift in the leading edge and tension crack in the trailing edge of the slope.According to the in-situ geological survey of Shilong Road landslide in Jiangning,Nanjing,the stratigraphic structure of the landslide is characterized by the dualistic geological structure that the upper part is fine and the lower part is coarse.This study chose Shilong Road landslide as an example to analyze its failure characteristics.Based on the basic principles of simple confined water distribution model and simply supported beam model,this paper attempted to analyze the mechanical mechanism of uplift and failure in aquiclude of front section of the slope under the action of temporary confined water.Aiming at the uplift characteristics of leading edge of the landslide,a one-dimensional steady flow model was constructed to analyse the distribution characteristics of confined water in the permeable layer of front slope.The simply supported beam model was introduced to analyse the influence of confined water uplift pressure on the deformation and stability,and the law of cracks development in aquiclude.The criterion of failure after uplift of aquiclude was determined,and the influence of uplifted pressure head at the foot of slope and thickness of aquiclude on the failure characteristics of aquiclude was analysed in detail.The results show that confined water head in the permeable layer is triangular distribution.The deepest crack in aquiclude develops at the maximum bending moment of uplift pressure on simply supported beam model.The maximum damage area of aquiclude is positively correlated with the uplift pressure head at the foot of slope and negatively correlated with the thickness of aquiclude.The critical uplift pressure head and the critical thickness of aquiclude are approximately linear when the aquiclude occurs uplift-tension failure.