Abstract: Currently, researches on the mechanism of landslides in red gently inclined formations in the Eastern Sichuan Province mainly focus on the change of seepage fields induced by the rainfall. This paper selects the Tiantai Landslide in Xuanhan County, Sichuan Province to study the influence of the slipped soil zone on the stability of the landslide in the area. The shear strength of the samples from the slipped soil zone of the Tiantai Landslide under both natural moisture and saturated conditions are laboratory tested. The test results show that the shear strength of saturated soil samples is significantly less than the strength of the samples under the natural moisture conditions. The Geostudio software is used to model the seepage field change induced by rainfall. The factor of safety for slope stability is computed using shear strength of the slipped soil zones under both natural moisture and saturated moisture conditions. The computational results show that shear strength of the slipped soil has a significant influence on the stability of the landslide. The existing research indicates that the landslide occurred due to the combined effect of both the stress field change and the shear strength reduction in the slipped soil zones induced by the rainfall.

Key words: Landslide in Red Gently Inclined formation, Mechanism, Shear Strength of Slipped Zone, Seepage Field, Factor of Safety for Slope Stability