Failure Mechanism of Thick Colluvium Landslide Triggered by Heavy Rainfall Based on Model Test

The mechanism of rainfall-triggered landslides is a key issue for the development of meteorological warning, risk assessment and engineering treatment of landslide disasters. In this paper, the Badong Yanzi landslide in the Three Gorges Reservoir area was selected as a typical example, and the physical model of the landslide was designed and produced. By setting three heavy rainfall conditions, the soil pressure, pore water pressure and moisture content data at different positions of the landslide can be monitored at all times. According to the test results, combined with the dynamic theory of colluvium landslide and numerical simulation analysis, the deformation characteristics and failure mechanism of thick colluvium landslide under heavy rainfall conditions were discussed. Test results show that under the condition of heavy rainfall, the deformation of the landslide started from the topographic turning point at the trailing edge of the slope. Heavy rainfall caused the soil pressure, pore pressure and moisture content data inside the landslide to rise to varying degrees, and the rise in the slip zone was significantly greater than the shallow surface of the landslide; after the extreme rainfall of 100 mm/h, the landslide began to creep slowly and then underwent a failure evolution process of acceleration, short deceleration, and acceleration again until the destruction process stopped. The trigger mechanism of the landslide is analyzed as follows. In the early stage of rainfall, the slope surface is dominated by pore infiltration, and the formation of rear edge fissures has become the dominant seepage channel for rainwater infiltration. The infiltration of rainwater causes the groundwater level of the slope to rise, the hydrostatic pressure of the fissure at the trailing edge of the landslide increases, and the erosion and collapse of the slope toe leads to seepage drainage points on the front edge of the landslide, resulting in hydrodynamic pressure. And the strength of the sliding belt continues to decrease under the effect of long-term soaking and softening. The landslide eventually undergoes overall slippage caused by shifting under the shear failure of the sliding zone.