Reactivation characteristics and genesis analysis of the large ancient landslide in Hongzhai, Qinglong County, Guizhou Province

On September 17, 2020, a landslide occurred in Hongzhai Village, Jichang Town, Qinglong County, Guizhou Province, resulting in serious damage to 134 houses and emergency evacuation of 569 people from 127 households. Investigation revealed that the Hongzhai landslide is a deep-seated large-scale landslide with a volume of approximately 6.25×10⁶ m³. Although surface buildings and infrastructure were severely damaged, the overall movement distance of the landslide was extremely short. Through comprehensive analysis including terrain geomorphology, rock and soil structure and material composition analysis, assessment of hydrological changes, and disclosure of multiple slip surfaces through borehole drilling, it was concluded that the Hongzhai landslide is a resurrected ancient landslide along bedding planes. In order to analyze and study the deformation characteristics and resurrection causes of the landslide, methods including UAV aerial survey, engineering geological survey, rock and soil mass investigation, and geophysical exploration were employed to obtain detailed data on disaster development characteristics, influencing factors, and identification features of ancient landslides. The results show that the Hongzhai landslide can be divided into four zones (A, B, C, D) based on deformation and stress transfer direction, with zone B further divided into subzones B1 and B2 based on relative displacement. The deformation and resurrection of the landslide occurred under the joint effects of steep terrain, complex rock mass structures, weak engineering rock masses, and continuous surface infiltration. Various features such as the arm-chair shaped topography at the back edge of the landslide, material differences between the slide body and surrounding rock and soil masses, fault-cutting front edges, and changes in hydrological sedimentation verify the existence of the ancient landslide.