Abstract: The damage and broken of falling rocks due to collision and velocity of fragments are crucial to the accurate prediction of trajectory of falling rocks. In order to reveal the collision damage and fragment velocity, a three-dimensional discrete element modeling of crystallization method is used to simulate the collision damage of ball and gravel based on experimental tests. The simulated results show that the collision damage patterns of ball and gravel agree well with that of the laboratory results. Higher collision velocity causes the radial and secondary macro cracks, breaking the rock gravel into small pieces. The secondary macro cracks result from the compression of orange-slice-shaped fragments. The radial macro cracks leads to a significant increase in the number of micro cracks. The damage rate based on the number of cracks shows three different stages with increasing collision speed. The contact force is also strongly affected by the damage and fragmentation of rock spheres. The simulation results show that the fragmentation of rock gravel collision can lead to high-velocity fragments. The maximum fragment velocity can reach up to 3.2 times of the collision velocity. The equivalent size of the high-velocity fragments is generally less than 0.11. After the collision, the velocity direction of fragments changes significantly with the collision velocity, which corresponds to the crushing mode of ball and gravel collision.

Key words: falling rock impact, broken pattern, impact force, damage ratio, high-velocity fragments