Deformation response and mechanical analysis of the Wangjiashan landslide in Baihetan Hydropower Station, China, during initial impoundment

Since the initial partial impoundment of the Baihetan Hydropower Station in Jinsha River watershed in early April 2021, many landslides have started undergoing rapid deformation. The Wangjiashan landslide has been the most active and dangerous landslide in the Baihetan Reservoir area. Based on road deformation data, the overall average displacement rate of the landslide before impoundment was estimated to be in the range of 11–14 cm/year. After impoundment, particularly after the water level rose to approximately 790 m above sea level (asl) between September to October 2021, the average displacement rate at various monitoring sites ranged from 200 to 600 mm/day, and the maximum value was 1002.6 mm/day. When the water level decreased to approximately 796 m asl, the landslide displacement rate immediately decreased to a range of 2–3 mm/day. The deformation of the Wangjiashan landslide was positively correlated with the rise in water level. The landslide mechanism before impoundment was active–passive failure, and soil mass damage accumulated in the transition zone (Prandtl wedge) between the active and passive blocks. The landslide was strongly affected following reservoir impoundment, with the failure mechanism transforming into a composite active–passive impoundment-accompanied failure. Under the high water level during partial impoundment in 2021, the soil mass in the transition zone of the landslide had yielded and was already in the critical sliding failure stage. Studying the Wangjiashan landslide is significant to understand the response of reservoir-induced landslides in Jinshajiang River valley and similar reservoir-induced landslides around the world.