Rockfall fragmentation upon slope impact based on discrete element simulation

Abstract

Objective The impact and fracture of rockfall are important reasons for the difficulty in predicting movement trajectories, and the geometric characteristics of slope bodies are key factors affecting the movement. Methods To study the crushing process of rockfalls and the influence of slope geometry characteristics on the movement of rockfall blocks, discrete element method (PFC2D) simulation technology was used to establish a rockfall free-fall-impact model to analysethe rock mass structure and slope geometry characteristics of typical rockfall disaster points. The fragmentation process of rockfall under different fall heights and impact angles is analysed, and the block motion velocity, crack number and impact force are obtained. Moreover, the two-parameter Weibull distribution is used to describe the fragmentation degree of blocks. Results The experimental results reveal that the fracture process can be divided into three stages: Contact-disintegration, extrusion-fragmentation and independent movement. Rock mass fragmentation starts at the impact point, disintegration occurs along the structural plane first, and fragmentation occurs on the new fracture plane. Sudden changes of the block velocity, crack quantity and impact force occur in the contact-disintegration and compression-fragmentation stages. The block velocity plummets, exhibiting a "step effect", and the impact force rises sharply, revealing a "double peak phenomenon". Moreover, when the fall height increases or the impact angle decreases, the "step effect" and "double peak phenomenon" become more obvious. Under the same impact angle, an increase of the fall height results in the increase of impact kinetic energy, thus increasing the degree of fragmentation and decreasing the particle size distribution range and characteristic particle size. At the same fall height, an increase in the impact angle causes that the contact area is reduced, and the degree of breakage is reduced, increasing the particle size distribution range and characteristic particle size. Conclusion The present results provide technical support for revealing the impact fragmentation mechanism of rockfall slopes and predicting the trajectory of block motion.

Keywords

• rockfall
• dynamic fragmentation
• discrete element method(dem)
• weibull distribution
• slope impact