Study on the multi-stage instability mechanism of the Wachangwan landslide in Gaoxian County, Sichuan, China.

Landslides are one of the most common natural disasters worldwide. On September 27, 2020, a large-scale landslide occurred in the Tianzhulin area of Huangni Village, Wenjiang Town, Gao County, known as the Wachangwan Landslide. Through field investigations and UAV aerial photography, the causes and deformation processes of the Wachangwan landslide were thoroughly revealed. Additionally, the displacement and deformation of the landslide were analyzed using the discrete element method. The key findings are as follows: The Wachangwan landslide is a typical multistage landslide. Prolonged heavy rainfall induced sliding in the front part of the landslide body, which dragged the rear, less stable soil mass, further exacerbating deformation and eventually forming a multistage landslide. The non-sliding zone is located between zones III-1 and III-2, influenced by pressure from adjacent sliding zones. However, based on rainfall data and displacement monitoring, the non-sliding zone remains generally stable at present. Using the discrete element method, the deformation mechanism and subsequent evolution of the Wachangwan landslide under rainfall conditions were analyzed. The landslide exhibited a failure mode characterized by traction, tensile fracturing, and sliding. A stability calculation method for multistage landslides under rainfall conditions was established, combining the traditional transfer coefficient method and the multistage landslide effects. By analyzing the current stability of the Wachangwan landslide, the results provide a novel approach for evaluating the stability of multistage landslides.