Seismic response and failure mechanism of rock slope at tunnel entrance using frequency domain analysis

The seismic stability of the rock slope at tunnel entrances is very intricate because of the interactions among geological structures and earthquakes. However, the local damage mechanism and the correlation mechanism of accumulated damage and landslide triggering are not clear. To investigate the correlation between the inherent frequency and seismic characteristics of a layered slope at a tunnel entrance from the perspective of the frequency domain, a three-dimensional finite element modal analysis and Fourier spectrum analysis of shaking table tests were carried out. This work takes the quarry slope at the tunnel entrance in Xiamen City as a case example. The study region is predominantly affected by strong seismic activity, where the rock is primarily composed of granite with varying degrees of weathering. The results show that the seismic energy below the tunnel is mostly focused on the low-frequency ranges, whereas the energy above the tunnel is gradually transferred to the high-frequency range. By analyzing the peak spectrum value of high-order inherent frequencies for the slope, its seismic damage evolution can be effectively identified, including fracture initiation, accelerated deformation, and sliding instability stages. The seismic response of the slope includes multi-mode interactions, which mainly include bending, torsion, and combined deformation. There are magnification effects of elevation, slope surface, and structural plane in the slope. Moreover, the triggering mechanism of the local deformation and integral sliding for the landslide is identified, which indicates that the lining structure of the tunnel entrance is more prone to seismic damage. This work successfully investigated the seismic damage evolution and failure mechanism of the slope at tunnel entrances in the frequency domain.