Evolution model and failure mechanisms of rainfall-induced cracked red clay slopes: insights from Xinshao County, China

Red clay landslides are widely distributed worldwide, resulting in severe loss of life and property. Although rainfall-induced red clay slopes have received extensive attention, the role of cracks in the evolutionary process of red clay slopes and their connection to failure mechanisms is still poorly understood. A comprehensive approach integrating field investigation, laboratory tests, and numerical simulations was conducted to study the 168 red clay landslides in Xinshao County, China. The results show that red clay is prone to forming cracks at high moisture content due to its low swelling and high shrinkage properties. The failure mode of red clay slopes can be summarized in three stages: crack generation, slope excavation, and slope failure. Furthermore, the retrospective analysis and numerical simulations of the typical landslide in Guanchong indicated that intense rainfall primarily impacts the shallow layer of soil within approximately 0.5 m on the intact slope. However, cracks change the pattern of rainfall infiltration in the slope. Rainwater infiltrates rapidly through the preferential channels induced by the cracks rather than uniformly and slowly from the slope surface. This results in a significant increase in both the depth of infiltration and the saturated zone area of the cracked slope, reaching 3.8 m and 36.2 m², respectively. Consequently, the factor of safety of the slope decreases by 13.4% compared to the intact slope, ultimately triggering landslides. This study can provide valuable insights into understanding the failure mechanisms of red clay slopes in China and other regions with similar geological settings.