Deformation characteristics and reactivation mechanism of giant ancient landslide in Wumeng Mountain area: case study of Daguan ancient landslide

The giant ancient landslide has a large influence area and strong concealment, which seriously threatens the safety of lives and properties of the urban residents in the canyon area. In order to understand the current state of the giant ancient landslide in Daguan and predict its future development trend, the basic characteristics, deformation process and resurrection mechanism of the ancient landslide are analyzed by using the high-precision remote sensing interpretation, UAV survey, field fine-adjustment survey, indoor rock and soil mass tests and numerical simulation. The landslide include three gentle slopes according to its topography, which are accumulated in multiple periods during the evolution of complex slopes in geological history. The ¹⁴C dating of organic matter in the deep slip belt reveals that the landslide was developed about 35000 years ago. The plane area of the ancient landslide is about 385×10⁴ m², and the volume is about 2.1×10⁸ m³. According to the deformation degree, it can be divided into four deformation zones. Under the influences of multiple factors such as rainfall, earthquake, geological environment and human engineering activities, creep deformation occurs in many parts of the slope at present. The numerical simulation results show that under the condition of one rainfall in 100 years, several secondary landslides slide on the ancient landslide, and the overall stability coefficient is 0.98, with the possibility of overall sliding. Under the strong earthquake condition, there may be deep sliding in the front and middle and rear areas of the ancient landslide, and the overall stability coefficient is 0.93. The research results may provide reference for the studies on the revival of such giant ancient landslide in the canyon area and disaster prevention and mitigation.