Seepage-deformation mechanism of colluvial landslides under the action of reservoir water level decline and rainfall

Objective With the construction of reservoir projects, the problem of deformation and instability of colluvial landslides in reservoir areas has become increasingly prominent. These landslides often experience deformation during the period of reservoir water level decline particularly exacerbated by rainfall. Therefore, the seepage-deformation mechanism of landslides under the joint action of reservoir water level decline and rainfall is one of the key scientific issues. Methods In this paper, a typical colluvial landslide in the Three Gorges Reservoir Area, the Shilongmen landslide, is used as a prototype. Physical model tests were designed to observe the macroscopic phenomena of the slope body and the pressure changes in the slope during combined scenarios of reservoir level drops and rainfall of different intensities, revealing the seepage-deformation mechanism of the colluvial landslide under complex hydrological conditions. Results The test results indicated that the decrease in reservoir level has a more obvious effect on the control of seepage at the front of the slope, while rainfall significantly raises the water head at the middle and rear of the slope, and the combination of the two will increase the hydraulic gradient in the slope, thus inducing slope deformation. Conclusion The seepage-deformation mechanism of the colluvial landslide when the reservoir level drops is as follows: In the absence of rainfall, only shallow surface scouring action occurs due to the difference between the internal and external heads of the slope. Under the condition of the worst rain in a 100-year rainstorm, cracks appear near the high water level, and then overall deformation occurs, with a maximum displacement of 58.3 mm. This study can provide a theoretical basis for the prevention and control of colluvial landslides under complex hydrological conditions.