Micro-characteristics and meso-shear mechanism of the soils of a slip zone in a landslide

The microstructure characteristics of slip zone soils and the variation law of microstructural parameters during shearing are the focus of the study of landslide mechanism, which is of great importance for the study of landslide prevention and control technology. Providing satisfactory explanations at the macro view is impossible because many phenomena occur after the soil is stressed in a slip zone. At present, the microscopic and meso analyses of slip zone soils are single and emphasize the macroscopic strength and deformation characteristics of slip zone soils during shearing. This study takes the landslide on the south slope of west open-pit mine in Fushun as the research object. The mineral composition and micro-characteristics of slip zone soils were studied with an X-ray diffractometer and a scanning electron microscope. Discrete element method was used to simulate the direct shear test. The meso parameters of slip zone soils were obtained by matching the direct shear test curve. The comparative analysis of meso parameters, such as the meso displacement vector field, distribution of maximum and minimum principal stresses, contact force chain, and evolution of normal and tangential contact forces, with four groups of particle gradations under different weathering conditions was conducted. Results show that the main mineral compositions of slip zone soils are original mineral-quartz and secondary mineral-clay minerals. The content of montmorillonite in clay minerals is relatively high, reaching 43.8%. The particles of slip zone soils are mainly flakes, with compact structure, and have obvious characteristics of oriented arrangement. Slip zone soils with a low degree of weathering contain coarse particles (quartz). The shear stress-displacement curves of slip zone soils with four groups of particle gradations show a strain hardening trend. Particle gradation affects the macroscopic and microscopic geotechnical and mechanical properties of slip zone soils. The displacement zone of the displacement field after shearing under poor gradation is characterized with large particles as the boundary, and its dilatancy is pronounced under the same normal stress. When the gradation is good, the particles have contact force chain, normal direction, and shear. The distribution of directional contact force before shearing is relatively uniform, the grading of large particles is mostly poor, and the stress concentration is considerable. In the case of poor grading, the distribution range of normal and tangential contact forces after shearing is smaller than that of good grading. The distribution of contact force in the same direction angle shorter than that in the case of good grading.