## 4 Discussion  
The rockfall shape and the geometry of the sloping terrain had a crucial impact on the accuracy of the rockfall prediction model [11]. Although many researchers have used terrain models with a degree of complexity [11; 19], they are still macroscopic predictions on a relatively large scale, and cannot accurately predict the affected area and final resting position of rockfall according to the practical terrain. Thus, we imported the DEM data of the study area into 3 DEC with suitable precision. Then, the geometry of the local joints and slope terrain was explicitly used to generate polyhedrons in the source area through field investigation. The simulation results (Figure 12) show that, in the case of a large number of blocks, the movement characteristics were consistent with the previous research  
Figure 17: Topographic angles measured on slope profile [5]. Figure 18: Rockfall resting position. (**a**) Contour map; (**b**) estimated distance of different contours. results [11; 19]. However, the calculation speed of 3 DEC increased with the number of blocks [9], indicating that it had obvious advantages when the number of blocks was large. Moreover, the final resting position of the rockfall (Figure 13) shows that the rockfall's trajectory had a significant correlation with the terrain relief. This correlation further increased as terrain accuracy increased. Furthermore, few related papers dealt with the performance comparison of 3 DEC and previously popular 3D-DDA. As far as the current research results are concerned, due to the increasing number and irregular shapes of blocks, 3 DEC may be more efficient and have better application prospects for the simulation of large-scale rockfall hazards. On the other hand, the COR, as an important parameter to describe the energy dissipation in rockfall collisions, directly affects the prediction accuracy [3]. Therefore, after considering the geological conditions (lithology, weathering degree, and other parameters) of the predicted slope, the COR value of the field test was also considered (we referred to [PERSON] et al. [42] with similar geological conditions, that is, \(R_{\rm n}=0.35\)) through field tests [38] to verify the rationality of the trajectory prediction model at this COR value. The trajectory of the proposed approach was more consistent with the field test and more suitable than [PERSON]'s [20] numerical prediction. After the proposed approach had been verified, the experiments were carried out on rockfalls of different sizes when \(R_{\rm n}=0.35\), and the corresponding values of multiple sizes and input parameters were obtained. Then, the parameter values corresponding to the rockfall size were input into the 3 DEC model of the predicted slope to determine the key parameters of the energy dissipation of the rockfall movement. Previously, the accuracy of simulation results was often verified by referring to historical disaster ranges [8; 9; 10] or field tests [11; 19]. Therefore, this work can provide a new method for the approximate prediction of rockfall hazards. That is, in the absence of historical rockfall events or field tests on a specific slope, a reasonable COR is adopted to describe the energy consumption in rockfall collisions. The rockfall movement trajectories on complex geometric slopes can be simulated from this. There are also some limitations in this paper that need further research. First, COR was mainly selected on the basis of experience, and simulations with multiple CORs were not performed. While the simulation results still provide useful reference for research, it would be preferable if more simulation data were available for comparison. Second, the factors affecting the selection of the COR value were not considered comprehensively. Most of the mechanical rockfall parameters in this proposed approach were empirical values, and it is necessary to conduct a sensitivity study between the mechanical properties and the COR value of the rockfall.