Fragmental rockfall is one kind of common geological disaster in mountainous areas. In this paper, the discrete element method, particle flow code (PFC) is used to simulate the impact and fracture process of rock mass, analysis the impact process of rock mass at different falling heights and impact angles, and the variation trend of impact force, velocity and the number of cracks in the rock mass. The results show that the velocity of rock mass decreases sharply and the crack develops rapidly after impact on the slope. With the increase in falling height, the rock mass velocity changes in a "second step shape", and the number of broken blocks increases while decreasing the rock mass size. With the increase of slope angle, the "double peak phenomenon" of impact force becomes less obvious. The results provide a theoretical basis for the numerical simulation of fragmental rockfall and hazard assessment.
Rockfall hazards, including small-scale blocks, falls and large-scale rock avalanches, are the result of tension-based damage to slope geotechnical bodies. This is one of the most common geological hazards in mountainous regions of southwest China, characterized by extensive distribution, high abruptness, and disaster-causing potential. On June 24, 2017, a high-level rock avalanche in Xinmo village, Mao County, Sichuan, with a volume of 45×105 m3, demolished 64 farm buildings and killed 73 people. After a high-level rockfall destabilizes and damages, high potential energy is converted to high kinetic energy, and then a huge number of fragmented blocks travel in the form of granular flow with enormous destructive force. Rock blocks are typically regarded as rigid bodies, such as Tang (2003) used recovery coefficients to characterize the velocity change during inelastic collisions when establishing the equations of motion in the collision phase; He (2009) obtained the impact force from the viewpoint of energy conservation using the principle of elastic-plastic mechanics. However, a large number of cases have demonstrated that impact fragmentation of crumbling bodies and slopes is a common occurrence, particularly for rock bodies with high weathering and low strength, which greatly increases the hazard risk due to the fragments’ varying sizes and independent motion trajectories (Figure 1). Thus, it is essential to examine the impact fragmentation process to enhance our understanding of the dynamics of rockfall dangers and to design efficient preventative and control strategies.
