Staged deformation evolution of extra-large accumulation landslides under hydrodynamic actions

The Yemaomian landslide, the largest near-dam accumulation landslide in the Three Gorges Reservoir area, is situated 17 km upstream of the Three Gorges Dam. Nearly 20 years of monitoring data indicate that the landslide has been undergoing slow deformation with a low deformation rate and magnitude. This paper applies a stepwise linear regression method and a mechanical model of hydrodynamics triggering to deeply explore the relationship between geological conditions, external factors, and deformation characteristics. Based on the stage transition characteristics of external triggering factors, the deformation evolution process of the landslide since the reservoir impoundment is divided into three stages: (1) June 2003 - September 2006, the landslide was reactivated by the significant rise in reservoir water levels, in a retrogressive mode; (2) October 2006 - September 2018, the deformation mode shifted from retrogressive mode to creep deformation as a whole, primarily due to the degradation effect on the landslide mass caused by immersion in reservoir water. (3) October 2018 - February 2024, a further significant reduction in the overall deformation rate and the impact of seasonal rainfall on landslide deformation surpassed that of reservoir water level fluctuations. The main component of landslide deformation is convergent creep, and extreme rainfall will be an important triggering factor for the local instability. Identifying the deformation evolution stages and determining the dominant external influencing factors at each stage is crucial for landslide research, and this paper provides an effective research paradigm for this purpose.