Abstract: To study the effect of mechanical property of freezing-thawing interface on slope stability, we carried out a series of direct shear tests of soils and ice-soil interfaces for saturated or nearly saturated gravel soil, silt, and clay under different normal stresses. Results show that the shear stress-deformation behaviors of gravel soil and corresponding thawing-freezing interface are all elastic deformation with clear peak shear stress. Silt, clay and corresponding thawing-freezing interfaces have plastic deformation within a small range, and there is no peak shear stress. Moisture content has little effect on shear strength of gravel soil in active layer, with little decreasing of the friction angles of gravel soil and ice-gravel soil interface with the increasing of moisture content. But for silt clay and clay soil, the effect of moisture on strength shows great decreasing of the cohesive force with the increasing of moisture content. We find that slope instability occurred more likely in the fine particle soil slope. Compared to silt soil, the corresponding thawing-freezing interface has a stronger resisting shear deformation ability, and the sliding slope will be in thawing soil layer above the interface, but the opposite the case for the clay soil. At the same time, the fine-grained soil slope tends to slide before reaching its maximum thawing depth. The higher the slope gradient, the earlier the time of instability. The main reason of slope failures in permafrost regions contributes to the lower cohesive force of sliding surface resulted from the higher moisture contents in active layers and the pore water pressure can affect the slope stability, and the influence of depth of water layer need to be taken into account.

Key words: slope failure, freezing-thawing interface, direct shear teat, failure surface, permafrost