Study on disaster characteristics and instability mode of shallow soil landslide in red bed area of southwest Sichuan Province

The red bed develope in southwestern Sichuan, and the shallow soil landslides in red bed area exhibit characteristics of cluster occurrences, large quantities, and great hazards. Taking Xide County of Liangshan Prefecture as the research area, deformation and failure characteristics, physical and mechanical characteristics and instability modes of shallow soil landslides in southwestern Sichuan are studied by means of mathematical statistics, engineering geological surveys, drilling, trench exploration, as well as soil physical and mechanical tests. Statistical analysis was conducted on the characteristics of landslide development in 5 aspects: thickness, scale, slope, profile form, and slope structure. The landslides demonstrate features of shallow surface sliding to flow failure and multi-stage sliding. Additionally, the accumulation body is in a state of high water saturation and has obvious hierarchy. The decay law of material composition and shear strength of residual slope soil in the red bed is revealed. The dominant particle sizes of the soil are concentrated in 2–5mm and 0.075–0.25 mm ranges. As water content increases, cohesion briefly rises to a peak and then continuously decreases, while the internal friction angle decreases continuously. With increasing saturation time, both cohesion and internal friction angle exhibit a continuous decreasing trend. Combined with landslide examples, three instability models of red bed soil landslides in complex terrain are extracted. The research results can provide data support for disaster prevention and mitigation in southwestern Sichuan and provide reference for improving the targeted prevention and control capability of mass disasters in red bed areas.