Abstract: The Baihe landslide is a large ancient bedrock landslide induced by heavy rainfall, with the upper part of parallel layers and the lower part of slightly incised layers. According to field investigation, the causes and formation mechanism of the landslide are summarized. The particle flow code (PFC^2D) program is employed and the parallel-bond model is introduced to determine the relation between micro-parameters and macro-mechanical properties of soils in the sliding zone through biaxial compression numerical tests. In subsequence, the landslide geological model is established and  the progressive process of landslide is simulated numerically by the particle-flow discrete element method. The displacement, porosity and strain at some key parts of the landslide are monitored. The simulation results show that crack occurs first in the soils in the upper part along the bedrock plane, which leads to shear dilatancy of slip mass in the middle part, thus pushing the ancient slip mass in the lower part, and finally causes instability of the whole accumulation. The position and shape of sliding plane don’t need to be assumed, and the particles adapt their positions according to contact forces, and finally shear failure happens at the plane which has the smallest shear strength. The simulation could provide theoretical basis for decision-making of the project.

Key words: landslide, particle flow code (PFC), numerical simulation, progressive failure, parallel-bond model