Abstract: As a kind of rolling stone with large volume and mass, collapse, instability and long-distance movement with high-speed and high-energy for a rock boulder often lead to destructive disasters of the buildings and traffic lines along the runout pathway. The K4580 typical landslide along the G318 national road in Tibet Autonomous Region was taken as the engineering background, the characteristics and phenomena of the entire process of the collapse, instability and movement of the rock boulder were studied using 3D discontinuous deformation analysis (3D-DDA) method. The 3D-DDA numerical models of the rock boulder collapse were built for three slope shapes: slope shape without landslide, slope shape with shallow landslide, and slop shape after deep landslide. The accuracy of the 3D-DDA simulation results for the boulder movement was then verified based on an empirical model of transverse offset for the block movement. In addition, the instability mechanism of the boulder collapse was investigated; the movement trajectory and kinetic energy evolution were analyzed for the three slope shapes after failure. The results show that the 3D-DDA has the capacity to effectively simulate the whole dynamic process of the boulder collapse and instability, movement development, violent impact, collision, and terminate stages. The boulder collapse presents an instability mode that including the mode transformation of sliding→toppling-sliding→toppling→overturning-falling. The rock boulder movement is manifested by various movement forms such as collision, bouncing, flying, rolling and sliding, as well as 3D spatial movement characteristics such as transverse offset and lateral deflection. The boulder disaster may be induced once the rock boulder passing through the road and colliding with the viaduct. Under different slope geometric shapes from no landslide, to shallow landslide, and to deep landslide, the main factors all decrease as the slope shape changes such as the movement deviation, bouncing height, colliding time to the slope bottom, and final stability time of the boulder. Through the 3D-DDA analysis of the collapse and movement of the boulder, the whole movement process, influence range, impact energy, and terminate location of the boulder can be then predicted, which can provide a reference for the boulder disaster prevention and mitigation and measurement policy.

Key words: slope boulder, collapse and instability, movement characteristics, 3D-DDA, impact and collision