## 3 Results
### The Influence of Main Controlling Factors on \(R_{\rm n}\)  
Figure 8 shows that \(R_{\rm n}\) decreases as \(\eta\) increases, with a 53.75% reduction. To facilitate interpretation, \(\eta\) is classified into two levels: Low-level \(\eta\) refers to rocks that are more rounded, near-spherical, and symmetrical in form, typically exhibiting smoother surface characteristics. High-level \(\eta\), in contrast, corresponds to angular, irregular, and polyhedral shapes with more pronounced edges and surface complexity. This classification helps capture the influence of shape geometry on the rock's impact behavior, particularly in terms of energy dissipation and the resulting normal coefficient of restitution (\(R_{\rm n}\)). Notably, \(R_{\rm n}\) for low-level \(\eta\) is significantly higher than that for high-level \(\eta\). The collision behaviors captured by the camera reveal that the low-level \(\eta\) mainly exhibits point-face contact with the slope. In contrast, high-level \(\eta\) predominantly exhibits line-face and face-face contact, reducing the probability of point-face contact. Falling rock shape affects energy dissipation by altering the contact mode and deformation. As the contact areas between the rockfall and the slope surface increase, and the friction energy dissipation rises, this leads to high energy dissipation and a decrease in \(R_{\rm n}\). Figure 9 demonstrates a negative correlation between slope surface material and \(R_{\rm n}\). \(A_{\rm slope}\) is classified into two levels based on deformability and collision behavior of the slope surface material: Low-level \(A_{\rm slope}\) refers to rigid, non-deformable materials, such  
Figure 8: The effect of falling rock shape on \(R_{\rm n}\). Figure 7: Influence of seven typical controlling factors on \(R_{\rm n}\). The left four factors—falling rock shape (\(\eta\)), slope surface material (\(A_{\rm slope}\)), initial velocity (\(v\)), and slope angle (\(\theta\))—are identified as main controlling factors, while the right three—falling rock type (\(A_{\rm rock}\)), falling height (\(h\)), and falling rock mass (\(m\))—are identified as minor controlling factors. as concrete, which simulate highly compacted, engineered surfaces with limited energy absorption capacity. These materials result in higher rebound velocities and less energy dissipation during collision. High-level \(A_{\text{slope}}\) refers to soft, deformable surfaces, such as turf, which simulate natural, energy-absorbing slope conditions, typically found in vegetated or loose soil environments. These materials provide greater energy dissipation during rockfall collisions, leading to lower rebound velocities. This classification helps characterize how different types of slope surface materials affect energy dissipation during rockfall collisions and how these effects subsequently influence \(R_{\text{n}}\). When both the rockfall and slope surface interact, their combined effect determines \(R_{\text{n}}\), with the final \(R_{\text{n}}\) being influenced by the interaction. \(R_{\text{n}}\) has a 45.57% decrease. The low-level \(A_{\text{slope}}\) has high strength, hardness, and deformation recovery, resulting in high \(R_{\text{n}}\). However, as \(A_{\text{slope}}\) increases, collision contact areas increase (indicated by the dotted line in the plot) and deformation recovery decreases, resulting in low \(R_{\text{n}}\). The mechanical properties of the slope surface material influence energy transformation and dissipation. Materials with high strength and hardness exhibit strong deformation recovery, reducing plastic deformation energy dissipation and enhancing \(R_{\text{n}}\). However, materials with low strength and hardness have weak deformation recovery, resulting in increased plastic deformation energy dissipation and lower \(R_{\text{n}}\). Figure 10 shows that \(R_{\text{n}}\) decreases as \(v\) increases, with a 35.47% reduction. The falling rock trajectory reveals that at low-level \(v\), despite multiple collisions, the energy dissipation per collision remains low.