Dynamic Response Characteristics and Instability Mechanism of High-Steep Bedding Rock Slope at the Tunnel Portal in High-Intensity Seismic Region

Western China is a typical high-intensity seismic zone, where seismic and geological disasters are frequent. The tunnel portal slope is prone to earthquake damage, which has become the key and difficult point in engineering construction. To deeply explore the dynamic response characteristics and instability mechanism of high-steep slopes at tunnel portal under frequent earthquakes, a large-scale shaking table test was designed. This experiment mainly simulates the geological environment of a high-intensity earthquake area by applying microseismic waves several times. The test results show that the amplification coefficient of peak ground acceleration (PGA) at different stages decreases with increasing earthquake intensity and finally presents a 50% attenuation. The vertical wave has a greater effect on the dynamic response of the slope, mainly affecting the magnifying effect during the relative elevation of 0.3–0.7. The horizontal wave has a stronger amplification effect on the slope crest region. The nonconsistency of the acceleration amplification factor (M PGA ) and the dynamic change characteristics of the ∆M PGA can well identify the three stages of slope failure: the elastic stage (0–2 m/s 2 ), elastoplastic stage (2–5 m/s 2 ), and plastic failure stage (≥ 5 m/s 2 ). The seismic failure modes of the slope can be summarized as follows: tensile fracture is formed first at the crest and waist of the slope, shear failure occurs between the slope waist and tunnel, forming a sliding body gradually, and the slope toe uplifts and finally forms collapse failure. This work can provide a reference for the design of seismic technology for tunnel portal slopes in high-intensity areas. Highlights To deeply explore the dynamic response characteristics and instability mechanism of the high steep slope at the tunnel portal under frequent earthquakes, a large scale shaking table test was designed, focusing on modelling the geological environment of high intensity seismic region. The roc k mass degradation effect of complex geological slopes in high seismic regions is simulated by applying microseismic wave forms near the study area for many times. By analyzing the peak ground acceleration and its amplification coefficient, the dynamic response characteristics and instability characteristics of the slope are systematically studied. Waves in different directions have different control effects on slope failure, and complex wave field superposition exists between the slop