Abstract: In the geological mapping process of Luoquan section of Yinbai expressway, it is found that the landslides in Ranjiagou are distributed in pairs, and each landslide has very similar deformation and failure characteristics. Based on the field geological survey data, combined with the basic theoretical knowledge of the engineering geology and the geomorphology, the formation mechanism of paired loess landslides is studied. The basic conditions for the formation of landslides in Ranjiagou are complex topography, special stratum structure and geological structure. The main inducing factor of landslides is rainfall. The formation of the paired distribution landslide is that the water erodes the concave bank of the Ranjiagou first, causing the side slope to lose its support and lead to the traction sliding. The huge sliding mass flows into the gully and blocks it. The water in the gully gathers to form a barrier lake of a certain scale. After the lake water gathers to a certain extent, the water changes the channel and erodes the opposite bank slope, and then causes instability sliding of the opposite bank slope, thus forming the current paired distribution landslide. The formation process of the paired landslides can be divided into six stages, which are the erosion stage of the water on the concave bank, the unstable sliding stage of the concave bank slope, the erosion stage of the water on the convex bank, the unstable sliding stage of the convex bank slope, the water erosion stage of the landslide front and the formation stage of landslide secondary sliding surface.

Key words: Loess Landslide, Formation Mechanism, Rainfall Action, Paired Distribution
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