Discussion on the application of amplification effect of protrusions in seismic stability evaluation of high slopes at bridge sites

The protruding part of the high slope at the bridge site in the deep canyon area has typical geological and geomorphic characteristics of three faces exposed to the air and multiple unloading faces. Studying the seismic terrain amplification effect of the protruding slope is crucial for ensuring the safety and stability of the bridge site. This study investigated the seismic amplification effects and deformation mechanisms of the slope's protruding parts at the large bridge site and optimized the positioning of piers and abutments. The research results indicate: (1) Field investigation and numerical simulation comprehensively confirm the development of debris flow at the top of the slope bulge and the instability of the rock mass at the lower part of the main pier. These conditions have been significantly affected by historical earthquakes. The acceleration exhibits a nonlinear amplification pattern that is influenced by the slope height, and excavation exacerbates the acceleration amplification effect in the excavation area. The maximum amplification factor is at the waist and top of the bulge (ridge), and the maximum acceleration amplification factor (MPGA) reaching 3.2. (2) The acceleration Fourier spectrum amplitude of the high-frequency part of the slope ridge (5-12 Hz) generally exceeds that of the slope valley. Excavation leads to a decrease in the peak value of the Fourier amplitude of the upper slope of the pier and abutment, while the lower slope experiences an increase. The peak value of the Fourier spectrum amplitude near the excavation location initially increases and then decreases with the increase of peak acceleration. (3) The maximum slope height and the extreme value of amplification factor are limited in the seismic design code for buildings, potentially leading to an underestimation of the dynamic amplification effect of the bulge and resulting in a more hazardous seismic stability evaluation of the bulge. (4) To ensure the seismic stability of the bridge site slope, the optimal distance between the outer edge of the pier and abutment and the slope surface is determined to be 22-26 m. The research findings can provide valuable guidance for the seismic stability evaluation of high slopes with protrusions and the optimal design of pier and abutment locations.