Physical and mechanical properties of slip zone soil in loess-bedrock landslides and its evolutionary process

The evolution process of landslide is accompanied by the formation of sliding zone, so the physical and mechanical properties of sliding zone soil determine to a certain extent the formation mechanism and activity trend of landslide. The selected sliding zone soil of Dingjiagou landslide in Yan'an as the research object, through X-ray diffraction, electron microscope scanning and the laboratory tests, the physical properties, mineral composition, microstructure and mechanical properties were studied. Results show that the properties of the different parts of the sliding zone are different apparently. The water content, natural density, dry density, clay minerals, boundary moisture content, and fractal dimension of the particle size distribution of the leading edge sliding zone soil are significantly higher than that of the rear sliding zone soil; The shear curve of the leading edge slide soil shows strain softening under vertical stress. The trailing edge slide soil shows weak strain softening under low vertical stress and stable strain under high vertical stress. Based on the differences in physical and mechanical properties between the front and rear edges of the sliding zone, it is concluded that the evolution stages of this type of landslide is formation of the shear plane of the trailing edge→extension of the shear plane→penetration of the sliding zone.