Study on the influence of 3D pre-existing joint on rockfall fragmentation during impact based on discrete element method

Abstract

Rockfalls pose significant threats to human society as one of the three major geological hazards. Numerous joints developed internally during their geological formation, leading to their fragmentation in motion and affecting trajectory and accumulation range, thereby increasing the hazard uncertainty. There are few studies on the fragmentation of jointed rockfalls, and only some focus on the influence of terrain, impact angle, and material properties on rockfall failure with continuous mechanics and extended finite element methods. However, very few analyses of the fragmentation mechanism of 3D jointed rockfall are from the perspective of discontinuous medium mechanics. Based on the indoor experiments to acquire the calculation parameters and consider the fracture character, we use the Discrete Element Method (DEM) to establish an impact model of rockfall with pre-existing joints to address these. We conduct numerical impact tests on samples containing joints of varying lengths, inclinations, thicknesses, and positions. By proposing the volume fragmentation ratio and number of main fragments and calculating them, monitoring changes in crack propagation events, acoustic emission events, impact force, and energy, the study investigates the specific effects of joints on the impact fragmentation of samples. The results indicate that the Discrete Element Method with parameters corrected by fracture tests can realistically simulate the three-dimensional fragmentation of jointed rockfall under actual conditions, solving the problem of stress concentration at the crack tip in Finite Element analyses. The geometric parameters and spatial position of the pre-existing joint largely determine the fragmentation of rockfall and the shape of blocks after disintegration, significantly impacting the impact force and the kinetic energy of the bouncing stone. Among them, joint inclination and length greatly influence the overall fragmentation of rockfall. In contrast, the position of a side or centered joint notably influences the micro-cracks and local damage on the contact area of rockfall, and joint thickness close to the maximum radium of calculation particle affects fragmentation significantly.