Interpreting the influence of rainfall and reservoir water level on a large-scale expansive soil landslide in the Danjiangkou Reservoir region, China

Expansive soils are widely distributed in the Danjiangkou Reservoir region (DRR), China. In recent years, with a rise in the reservoir water level (RWL), reservoir-related expansive soil landslides have gradually become a serious issue in this area. However, few studies on reservoir-related expansive landslides have been reported. Taking the Jingang landslide as a case study, a detailed analysis was performed to interpret the movement characteristics of the landslide under the influence of rainfall and the RWL, based on the comprehensive in-situ monitoring data and laboratory soil tests. The Jingang landslide is a large-scale expansive soil landslide triggered by reservoir operation. Available data indicate that the displacement of the Jingang landslide displays step-like trends and mainly occurs during high RWL or filling operation periods. Both seasonal rainfall and RWL variation are important factors that cause the ground movement of a landslide. The onset of rapid ground movement usually corresponded to an RWL of 161-163 m a.s.l.. The motion pattern is primarily retrogressive, and the displacement velocity increases towards the toe, which could reach 41 mm/month. The free swelling rates of the soils in the Jingang landslide are approximately 40-60%. The stability calculation indicates that the factor of safety of the Jingang landslide decreases from 1.049 to 1.038 due to the swell pressure of expansive soil, and this has a significant adverse effect on the landslides.

Automated summary

Expansive soils are widely distributed in the Danjiangkou Reservoir region in China, and reservoir-related expansive soil landslides have become a serious issue with the rise in reservoir water level. This study conducted a detailed analysis on the Jingang landslide, a large-scale expansive soil landslide triggered by reservoir operation, to understand its movement characteristics under the influence of rainfall and reservoir water level. The data suggest that both seasonal rainfall and reservoir water level variation play important roles in causing ground movement of the landslide.