Catastrophic Landslide Triggered by Extreme Rainfall in Chongqing, China: July 13, 2020, Niuerwan Landslide

At approximately 7:00 a.m. (Beijing time) on July 13, 2020, a catastrophic soil and rock landslide occurred in Baima Town, Wulong District, Chongqing, China. With a length of 750 m and a width of 125m to 260 m, the landslide carried approximately 1.4 × 10⁶ m3 of rock and soil debris and destroyed eight houses, two main roads, a shale gas pipeline, and a large amount of farmland. Field investigation found that the reactivated deposits were still moving. The failure mechanism of the landslide was analyzed based on the geological conditions, deformation process and triggering factors. The research shows that the Niuerwan landslide had a complex deformation process. According to the deformation characteristics, the landslide was divided into five parts: the source area, the compression area, the rapid sliding area, the landslide-affected zone and the accumulation area. The source area was triggered by continuous torrential rainfall and controlled by mudstone and bedding plane. The variation of the microrelief in the study area has significant effect on the failure model of the landslide. Precipitation increased the weight of the sliding mass by saturating the soil and rocks, and the shear strength was decreased by water erosion. Consequently, the steep source area firstly deformed and impacted the middle part. Eventually, a continuous sliding surface developed along the weak layer, giving rise to catastrophic failure. Moreover, the accumulation area at the steep slope toe rapidly moved downward to form a debris flow under the combined action of the geological conditions and rainfall. The Niuerwan landslide is a complex rainfall-induced landslide with a unique evolution process, which can provide a reference for landslide disasters.

Keywords: Rainfall, deformation characteristics, failure mechanism, debris flow, Evolution process