Abstract: Suoertou landslide which originated in fault rupture zone is a super large landslide, the sliding zone soil of the landslide consists primarily of highly weathered phyllite and slate in the Middle-Upper Silurian. There is about 30% amount of coarse particles of which size is greater than 2 mm in sliding zone soil; so the coarse particles occupy an important position in the soil particle composition and have serious influence on the stability of the landslide. The large scale direct shear apparatus is used here to investigate the direct shear strength behavior of the sliding zone soil under different moisture contents. The results show that there is a strain-hardening feature in the curve of the relationship between shear stress and shear strain with different water contents when the controlled dry density equals 1.7 g/cm3; besides, the more is the normal stress, the more is the hardening feature. The shear modulus G0.1 which is the modulus when the horizontal shear strain is 10% increases with the increment of normal stress at the same moisture content, and the shear modulus has a negative linear relation with moisture content at the same normal stress. The relationship between shear stress and horizontal shear strain can be simulated well by using Duncan-Chang hyperbolic model; but it can't reflect the strain softening feature of the sliding zone soil.

Key words: Suoertou, sliding zone soil, moisture content, large-scale direct shear, hyperbolic model