Characteristics and initiation mechanism of the large mudstone Dongping landslide induced by heavy rainfall in Gansu Province, NW China

Abstract Background At approximately 4:00 PM on 18 July 2023, a heavy rainstorm lasting one hour triggered a significant mudstone landslide in Dongping, Weiyuan County, Gansu Province, Northwest China. The landslide resulted in the burial of houses, the fracturing and destruction of roads, and posed a serious threat to 16 households. The estimated economical loss from this disaster reached 3.2 million yuan. This study presents a detailed field investigation of the Dongping landslide, focusing on the deformation and failure characteristics through a multi-layered analysis of sliding strata, rock mass structure, slope configuration, and failure mechanism. Moreover, the study explores the key triggering factors of the Dongping landslide, with particular attention to the roles of seismic activity, rainfall, and preferential flow in the development of large-scale mudstone landslides. Results The stratigraphic profile of the Dongping landslide reveals a two-layer structure, consisting of overlying loess and underlying mudstone, with the sliding surface primarily located within the underlying Neogene red mudstone. The initiation location of the Dongping landslide is situated at the rear of the slope, while the main slip-resistant section is located in the middle section of the landslide, exhibiting a predominantly thrust-sliding. After encountering resistance in the middle section, the front part of the sliding mass continued to move, leading to the formation of secondary landslides. The overall movement of the Dongping landslide is characterized by rotational sliding, with the sliding mass remaining relatively intact. Conclusions The initiation of the large-scale mudstone landslide in Dongping was driven by multiple factors. The heavy rainfall served as the direct triggering factor for the landslide occurrence. However, some historical factors, including seismic activity and previous sliding surface, had already weakened the slope structure by degrading the mechanical properties of the landslide mass and creating preferential flow channels, thereby setting the stage for the Dongping landslide. Structural fractures in the landslide area, along with sinkholes formed by a combination of tectonic joints, soil properties, and human activities, constituted preferential seepage pathways for water within the slope. These pathways provided the hydraulic conditions necessary for rainfall-induced landslides, making them the primary controlling factors in the occurrence of the Dongping landslide.