Abstract: Along with the acceleration of urbanization process, a large number of engineering landslides are induced by artificial slope cutting in loess region. Feifengshan landslide has been selected as a typical case in order to study the mechanism of typical engineering landslide. Detailed field investigation has been done, meanwhile, in-situ water penetration test and soil water characteristic curve (SWCC) test on undisturbed loess and paleosol have been conducted in this study. The experimental results show that: The permeability coefficient of loess can reach medium grade about 10-4 cm/s, if loess has structural problems, such as small holes, cracks, and so on. The air entry value of paleosol is 11.5 kPa obtained by SWCC tests , which is higher than that of loess (9.0 kPa); at the same time, curve also indicates that the evolutions of strength and deformation of paleosol and loess will differentiate dry-wet cycle. With the increase of suction, the growth rate of shear strength of paleosol is lower than that of loess during drying phase, and the elastic volume shrinkage rate of paleosol, caused by compressing, is also lower than that of loess in the same process. Paleosol will have bigger expansion deformation than loess during wetting phase, because the clay content of paleosol is higher. On the basis of experimental results analysis and field investigation, it is founded that artificial slope cutting is the most important factor inducing Feifengshan landslide, which triggers a series of physical and chemical chain reactions, especially reinforces coupling effect between soil and water and accelerates the occurrence of landslide. Finally, we put forward the failure mode of Feifengshan landslide characterized by two-way development of sliding surface and typical progressive destruction, simultaneously having part of geological features of slumping.

Key words: loess landslide, artificial slope cutting, in-situ permeation test, soil water characteristic curve (SWCC), suction