The initial impoundment of the Baihetan reservoir region (China) exacerbated the deformation of the Wangjiashan landslide: characteristics and mechanism

Reservoir landslides greatly threaten reservoir safety. Understanding the deformation characteristics and mechanism of reservoir landslides can help evaluate their stability and prevent secondary disasters. A detailed analysis of the deformation characteristics and landslide reactivation mechanism of the Wangjiashan (WJS) ancient landslide during the initial impoundment of the Baihetan Reservoir region was performed using comprehensive in situ monitoring and drilling data. The WJS landslide slowly deformed before impoundment. Reservoir impoundment was the main factor driving the intensifying deformation of the WJS landslide. The rise in reservoir water resulted in bank collapse at the landslide toe. After the reservoir water flooded the sliding zone of the landslide toe, creep deformation occurred along the deep sliding zone, which developed into overall sliding on July 7. The further rise in the reservoir water level has led to the rapid sliding of the landslide. The WJS landslide is a buoyancy weight-reducing landslide. When the reservoir water rises to a high level, the buoyancy force of the reservoir water acts on the resisting section, which reduces the resisting force and leads to the rapid sliding of the landslide. When the reservoir water level drops from the high level, the buoyancy acting on the resisting section decreases gradually, and the stability of the landslide can be restored. At present, the WJS landslide deformation rate gradually decreases with the reservoir water level, and the probability of large-scale landslides is low. However, WJS landslide monitoring needs to be strengthened to more closely study its deformation mechanism.