Activation mechanism and failure process of an ancient landslide induced by landslide impact loads in China

On September 9, 2021, a catastrophic landslide occurred in Zhanjiaping Village, Zhenba County, Shaanxi Province, China, blocking the Yushui River and forming a landslide barrier lake. To gain a deeper understanding of this catastrophic event, we have utilized a combination of engineering geological exploration, multi-source remote sensing and geotechnical testing techniques to elucidate the dynamic evolution and formation mechanisms of the landslide. Zhanjiaping landslide is located in the core of the Luoquanyan Syncline within the Daba Mountain foreland arc structure zone, with the plunge direction of 319° and plunge of 11° along the fold axis. Zhanjiaping landslide is developed in the ancient landslide area, which is a typical sliding and tension-fracturing landslide with a very gentle sliding surface, and the volume of the landslide is estimated to be 7.44 × 10⁶ m³. The strata in the landslide area exhibits a layered structure with alternating soft and hard formations. Under the influence of continuous rainfall, the steep slopes on the north flank of the Luoquanyan Syncline were destabilized along the bedding planes of the underlying mudstone, and forming a deposit on the gentle slope to the northeast of Zhanjiaping Village in the syncline core area. Then, affected by the landslide impact loading and rainfall infiltration, the strength of the contact surface between the paleoslide body and bedrock in the core area of Luoquanyan Syncline decreases, leading to the resurrection of the ancient landslide. However, blocked by the south flank of Luoquanyan Syncline, the downward sliding of the slide body was impeded, which in turn to both sides to undergo multiple extrusion and braking phenomena. This study provides a case study of a small landslide destabilization that eventually triggered the resurrection of a large-scale ancient landslide under the control of geological structure, which can provide a reference for the prevention and control of similar landslide disasters.