Abstract: A large model testing system was developed to simulate the rockfall impacting the slope of tunnel exit of Chengdu-Lanzhou railway which is under construction in the southwest area of China. The system is composed of the model testing bench, three-dimensional rockfall release device and high-speed photographic system. This system with high structural strength can meet the visual requirements in the testing process. Based on the measured physical and mechanical parameters of rock specimens, similar materials to phyllite and sandstone were developed to simulate slopes and rockfall by mixing with different proportions of vaseline, silicone oil, cement, fine sand, barite powder, gypsum and talcum powder. The effects of the initial slip angle, shape and mass of cuboid rockfall on the coefficients of restitution were studied through the physical model tests. Besides, a high-speed camera and coordinate callipers were adopted to record the complete trajectories of rock blocks during the rockfall process. At last, a video processing software was employed to analyze the variation of velocity before and after the collision between the rockfall and the slope, and the normal and tangential restitution coefficients of the rockfall were calculated by formulas. The testing results showed that with the increase of the initial slip angle, the normal restitution coefficient of the plate specimen increased, whereas the tangential restitution coefficient decreased and its variation was more obvious. The normal restitution coefficient had a remarkable decreasing trend with an increase of rock mass, but the tangential restitution coefficient seldom changed. For cuboid rock blocks, the normal and tangential restitution coefficients of cuboid specimens are larger than those of thick plate specimens. The normal and tangential restitution coefficients of strip specimens exhibited a polarisation trend due to different contact forms. Finally, the impact mechanism of rockfall was explored according to testing results and previous research results.

Key words: tunnel heading slope, dangerous rock collapse, model test, restitution coefficient, impact mechanism