垂直节理对黄土边坡稳定性影响分析

Stability analysis of loess slope considering the effects of vertical joints

黄土中垂直节理普遍发育,垂直节理的存在是导致黄土滑坡发生的重要危险性因素,针对黄土垂直节理对边坡稳定性的影响问题,采用室内试验的方法,通过分析含垂直节理试样的典型破坏方式及应力-应变关系,初步得到了含垂直节理试样的强度与破坏特点。进一步的,进行了含垂直节理边坡的安全系数解析计算,提出了分别含闭合垂直节理和张开垂直节理的边坡安全系数计算公式,最后通过有限元数值分析,计算了垂直节理的长度效应、临坡距离效应与倾角效应对边坡稳定性的影响。研究结果表明:(1)张开型垂直节理试样的强度小于闭合型,破坏速率大于闭合型;斜节理倾角为57°时,试样表现为低强度和沿节理面发生滑动破坏的特性。(2)垂直节理的长度与临坡距小于5 m时,垂直节理的存在对于边坡滑动面形状和位置的影响较小,当长度达到15 m,临坡距为10 m时,对高度40 m、坡度为45°的边坡的劣化程度达到峰值。(3)将垂直节理边坡的破坏总结为“沿节理面的拉裂和非节理部分的剪切”,滑坡后缘最大垂直拉裂至15 m后拉裂深度不再随节理长度与临坡距离的增加而增大;滑坡后缘的剪切破坏优势破裂倾角界于45°~65°之间。

Vertical joints are widely developed in loess,and the existence of vertical joints is an important risk factor that leading to the landslides.In view of the influence of loess vertical joints on slope stability,by analyzing the typical failure modes and stress-strain relationship of samples by triaxial compression test,the strength and failure characteristics of samples with vertical joints are preliminarily obtained.Furthermore,the generalized model of landslide with vertical joints is established,and the calculation formulas of safety factor with closed vertical joints and open vertical joints are proposed.Finally,the influence of length effect,distance effect and inclination effect of vertical joints on slope stability is calculated through finite element numerical analysis.The results show that:Firstly,the strength of simple with open vertical joint is small than that of the close joint simple,and the failure rate is higher than that of the closed one.When the angle of inclined joint is 57°,the specimen shows the characteristics of low strength and sliding failure along the joint surface.Secondly,When the length and the distance from the vertical joint to the slope surface are small than 5 m,the existence of vertical joints has little influence on the shape and position of sliding surface of slope.Thirdly,The failure of vertical joint slope is summarized as tensile failure along vertical joint plane and shear failure of non joint part.When the vertical tensile crack reaches 15 m,the tensile crack depth no longer increases with the increase of joint length and distance from joint to slope surface;the dominant fracture angle of shear failure at the back edge of landslide is between 45°and 65°.