Mechanisms of earthquake-induced unstable rock masses initiation and rockfalls impact on open-cut tunnels: insights from shaking table tests

High-steep rock slopes are highly sensitive to seismic activity, and unstable rock masses can easily initiate and impact tunnel entrances. In this study, a model of the slope–rockfall–tunnel system (SRTS) is constructed and then tested via triaxial loading shaking-table tests to investigate the seismic failure mechanism and interaction within the system. The dynamic response of the SRTS is analyzed, which reveals the initiation and damage mechanism of sliding rockfalls. Additionally, the force and deformation characteristics of structures during the impact of rockfalls on open-cut tunnels are identified. The findings indicate that the seismic responses of unstable rock masses and open-cut tunnels on the slope amplify significantly in the horizontal and vertical directions, respectively. Furthermore, Hilbert–Huang transform-derived trends of Hilbert and marginal spectra effectively captured the damage evolution in sliding rockfalls. Discrepancies in the energy and vibration frequencies across the weak structural plane predominantly govern the initiation of sliding rockfalls. Additionally, this study highlights that the longitudinal positioning of open-cut tunnels substantially affects the dynamic response of the lining structure, thus allowing one to identify the most vulnerable sections under the impact of rockfalls. These insights are instrumental in providing seismic protection and reinforcement strategies for tunnel openings in mountainous regions.