<b>Phase-Transition variations in Granular Materials under Multi-Period Vibrations: Implications for Triggering Landslides after Multiple Earthquakes</b>

Despite extensive research on the seismic responses of landslides triggered by single earthquakes, there is a lack of understanding of the seismic responses of landslides due to earthquake sequences and multiple earthquakes, and the mechanisms of dynamic weakening under multiple earthquakes still lack support from experimental results. We conducted multi-period vibrations ring-shear experiments to explore the seismic response characteristics. The experimental results showed that as the vibration period increased, post-vibration slip occurred, then gradually increased, and finally accelerated the instability. The granular medium phase transitioned from solid-semi solid to liquid. We then analyzed the changes in shear modulus under multi-period vibrations using a dynamic triaxial-bender system; the shear modulus progressively weakened with successive periods of vibrations. The amplitude of multi-period vibrations, the vibration time, and the interval time between two periods of vibration had important influences on the instability. Our study is helpful in understanding how multiple earthquakes trigger landslides.