Stress amplification of the landslide slip zone during vertical P-wave incidence based on ray theory

Abstract

The largest landslide triggered by the Wenchuan earthquake was the Daguangbao landslide, which formed in the preinterlayer structural dislocation zone (weak layer) in the slope. The weak layer suffered strong historical structural fragmentation and produced a large area of new fractures during the earthquake. The causes of weak layer fragmentation and its control effect on the initiation of the Daguangbao landslide have always been the research focus. In this paper, by taking the Daguangbao landslide as the geological prototype, the interlayer dislocation zone was generalized into a geological body model with a weak layer unit. Based on seismic wave ray theory, a dynamic response theoretical model of the vertical P-wave incidence process considering the wave field conversion and time delay at the top and bottom interface of the weak layer was established, and the dynamic stress amplification characteristics of the weak layer are found theoretically. Furthermore, through a shaking table physical model test, the influence law of seismic intensity and frequency on the stress amplification of the weak layer were revealed. Based on the theory and experimental structure, it was proposed that the amplitude attenuation was caused by the wave field conversion and energy distribution of the vibration wave at the top and bottom interface of the weak layer, and the time delay was caused by the difference in the medium properties between the weak layer and the upper and lower hard layers. Both of them lead to stress differentiation and superposition, which was the internal mechanism of stress amplification in the weak layer. Therefore, it was considered that the stress amplification of the preinterlayer structural dislocation zone of the Daguangbao landslide in the process of a strong earthquake led to the fragmentation of the rock mass in the zone, reduced the shear strength of the rock mass in the slip zone, and promoted the rapid start-up of the landslide in the process of a strong earthquake.

Keywords

• weak interlayer
• ray theory
• p-wave
• delay time
• stress concentration
• shaking table test