Large-scale toppling slope under water level fluctuation of reservoir: A case of Yunnan Province, China

Abstract

Landslides induced by reservoir inundation are common in Southwest China, negatively influencing hydropower stations. The Wunonglong hydropower station dam was constructed in the upper reaches of the Lancang River, accordingly causing the water level at the Lajinshengu slope to increase by 30 m. A tension crack with a visible depth of 8 m was observed in the upper sector of the Lajinshengu slope after reservoir impoundment for 170 d. In the following days, numerous cracks appeared on the surface of the slope, and the maximum displacement of the slope reached 3.22 m. Then, a large-scale active deformation body within the Lajinshengu slope formed with an area of 2.62 × 105 m2 and a volume of 1.65 × 107 m3. Detailed field investigations, on-site monitoring, and centrifugal model tests were carried out to analyze the surface features, deformation characteristics, and failure mechanism of the Lajinshengu slope. The results show that the slope is an ancient landslide, divided into two parts (i.e. zone A and zone B) by the gully. Zone B is a traction landslide caused by the displacement of zone A. The long-term inundation weakens the soft rock at the slope foot, intensifying the toppling of bedrock and consequently triggering the sliding of the overburden in zone A. The failure mode of the Lajinshengu slope is a typical case of toppling-sliding failure, and the underlying rock toppling drives the overlying sliding. In addition, early identification methods for toppling deformation covered by overburdened soil were proposed based on monitoring data and deformation signs.

Keywords

• Lajinshengu slope
• Reservoir impoundment
• Early identification
• Failure mechanism
• Toppling-sliding slope failure mode