Deformation characteristics, mechanisms, and dominant factors involved in rainfall-hydrodynamic pressure landslides: a case study

A 16-year surface macroscopic survey and global positioning system (GPS) monitoring of the Sanmendong landslide in the Three Gorges Reservoir Area of China demonstrated that the degree of deformation of the landslide correlated with rainfall and fluctuations in reservoir levels. In this study, the seepage field and stability coefficient of the Sanmendong landslide deformation were estimated under rainfall conditions, and fluctuations in the reservoir water level and their coupling effects were simulated and calculated. As the water level increased, the seepage force was directed toward the inside of the slope, creating conditions that bolstered landslide stability. However, when the reservoir water level drops or rainfall occurs, a seepage force is directed to the outside of the slope, hindering landslide stability. GPS monitoring data and the correlation between reservoir water-level fluctuations, rainfall, and landslide deformation were analyzed. The analysis revealed a positive correlation between rainfall and the displacement rate at monitoring point ZG361, with a high gray correlation degree (0.761). However, the correlation between the rate of fluctuating reservoir water levels and displacement rate at monitoring point ZG361 was insignificant. The stability calculation demonstrated that under normal Three Gorges Reservoir operation, a decrease in the water level decreased the stability coefficient by < 1%, whereas heavy rainfall decreased the stability coefficient by > 10%. The above results prove that rainfall is the primary driver governing the deformation of the Sanmendong landslide.