Experimental Investigation of Impact Configuration on the Coefficients of Restitution of Elliptical Blocks in Rockfalls

The influence of impact configuration and block shape on rockfall rebound behavior has been highlighted in numerous experimental studies. To further investigate these effects, an experimental campaign was conducted using rigid elliptical-disk blocks, allowing the simultaneous examination of block geometry and impact configuration under controlled conditions. The experimental setup was inspired by existing analytical approaches that employ elliptical geometries to describe rebound mechanics and to provide a more detailed interpretation of the parameters governing impact response. The results show that coefficients of restitution exhibit substantial scatter and do not display systematic trends with respect to the geometric aspect ratio of the elliptical disks (a/b ≈ 1.25–2.0), within the testing range of this experiment. Instead, rebound behavior is primarily controlled by impact configuration, as described by the orientation of the major axis and the impact angle. The following two distinct impact types were identified: instantaneous and rolling, associated with different responses. The experimental data were further used to assess existing analytical models, revealing limited quantitative agreement due to the idealized assumptions in their formulation. Overall, the study demonstrates that rebound response in rockfall processes is strongly configuration-dependent, emphasizing the need for modeling approaches that explicitly account for impact configuration and contact geometry.