中文摘要：

滑带土的残余强度一直是边坡工程研究的重点。由于剪切面微观结构在剪切前后的变化与宏观的土体强度存在必然的联系，所以针对一古滑坡滑动带的含砂黏土进行环剪试验，采用电镜扫描技术分析剪切前后微观结构的变化，探讨微观结构与土体宏观力学特征的关系。研究表明，含砂黏土的强度特征不同于一般黏性土，没有明显应变软化特性，粗粒含量对峰后强度有比较明显的影响。剪切过程会导致颗粒出现明显的定向性排列，微观结构发生改变，出现颗粒破碎、孔隙率提高，颗粒形状变狭长的现象，这与滑带土的宏观强度变化有密切的关系。另外，通过周长一面积法对剪切面颗粒形态的分形研究，发现剪切面土颗粒微观形态具有明显的分形特征，分形维数与滑带土的残余强度指标呈线性负相关关系。

英文摘要：

Residual strength of slip zone soil is the major concern of slope engineering. There is a close relation between microstructure of the shear surface and the strength. Ring shear tests are performed on the clay samples （containing sand） that were obtained from an ancient landslide slip zone. The scanning electron microscope is used to analyze microstructure of shear surface and its relationship with strength. Unlike most clay, the shear strength of the investigated slip zone soils exhibits a slight strain-softening, and increasing coarse fraction significantly influences the post-peak strength. Micro characteristics of shear surface show that the shearing process resulted in directional arrangement of particle and microstructure change, followed by coarse particles broken, void ratio increased and particle shape narrowed. Besides, fractal study of the particle by the perimeter-area method reveals that the particle form has a strong fractal feature, suggesting a good negative linear correlation with residual strength.