INVESTIGATION OF ROCKFALL IMPACT FRAGMENTATION BASED ON THE DEM

Rock falls are a common geologic hazard of rock slopes in mountainous regions. It normally causes significant hazards to human lives and lifeline facilities. Rock fragmentation is frequently observed in rock fall events. However, rock fragmentation upon impact is usually not accounted for in the design of defense structure. The trajectories of rock fragments are much different from that of intact block(used to design barrier) and are more difficult to predict with an increase in the risk of causing damage to properties and lives. Therefore, the mechanism of rock fall impact breakage plays an important role in the prevention of rock fall hazards. In particular, predicting the size, shape and number of fragments generated under impact is fundamental to design more efficient protection systems. In this paper, the Discrete Element Method(DEM) has been used to simulate the impact process of rock fall, such as the potential rock mass fragmentations induced by the dynamic impact. In these simulations, the spherical rock sample is regarded as an assembly of particles in which the adjacent particles are connected by a breakable bond, and the ground is represented by a rigid plate with a layer of particles fixed on the surface for the purpose of simulating the elastic deformation and friction of the ground. Employing the open source DEM code EsyS-Particle, the general features of rock fall are illustrated in details, regarding the rock block damage patterns(rebound, fragmentation and crush).Meanwhile, this study reveals how the evolutions of the number of broken bonds and the kinetic energy of the model are influenced by the micro-parameters, such as the bond Young's modulus, inter-particle cohesion and friction angle. Based on the numerical results, for sufficiently low ratios of the Young's modulus to cohesion, the rock block does not fracture but rebound. For using medium ratios, the rock block can break into many fragments. For sufficiently high ratios, the rock block can be crushed into very small dispersed grains. Our results indicate that the potential for impact fragmentation tends to reduce with the decreasing ratio of the Young's modulus to cohesion, while the friction angle has a little influence on the impact process.