Abstract: The collision and fragmentation patterns of rockfalls under the influence of joints were studied through physical experiments. Based on indoor collision tests, the discontinuous deformation analysis (DDA) parallel computing method was used to simulate the impact-collision-fragmentation process of rockfalls. The main focus is on discussing the influence of the angle β  between the joint and the slope, the connectivity rate k of the joint, and the impact velocity V of the rockfall on its crushing characteristics. The ratio η  of the surface area of the rockfall to its initial surface area is used as a quantitative measure of the degree of fragmentation, with a larger η  indicating a higher degree of fragmentation. The research findings are as follows: 1) η  increases with k; under high-velocity impact conditions, the η  value at k = 0.75 is 1.2 times that at k = 0.25. 2) When k = 0.25, η  does not vary significantly with β  ; however, when k = 0.50 and 0.75, η  decreases as β  increases. 3) The η  value under high-speed impact (6.8−7.4 m/s) is 1.5 times higher than that under low-speed conditions (3.5−4.5 m/s). 4) As the single-joint connectivity rate k of the rockfall increases from 0 to 0.75, the energy recovery coefficient exhibits a decreasing trend, with its value reduced by 1.6 to 1.9 times. 5) With the increase in impact velocity, the energy recovery coefficient of the rockfall gradually increases with the increase in joint angle β , up to 1.6 times. 6) The fracture characteristics and degree of fragmentation obtained through numerical simulation and indoor collision tests are basically the same. An increase in the single-joint connectivity rate and the angle between the joint and the slope surface affects stress propagation and alters the fracture characteristics of the specimens. 7) When a multi-jointed rockfall is impacted and broken, the cracks do not extend along the outline of the joint setting and do not intersect with joints far from the center of the rock. The velocity of the debris after impact is slightly lower than that before impact. This study has certain reference significance for revealing the collision and fragmentation patterns of rockfalls under the influence of natural joints.

Key words: collision and fragmentation, primary joints, rockfall disasters, physical tests, energy recovery coefficient