Failure mechanism investigation on loess–mudstone landslides based on the Hilbert–Huang transform method using a large-scale shaking table test

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Loess–mudstone landslides occur easily because of earthquakes or rainfall; they account for a large number of landslides in the loess area of China. The Buzi landslide was one of the two largest landslides triggered by the 2013 Minxian–Zhangxian Ms. 6.6 earthquake and resulted in two deaths. Field investigations showed that it was a loess–mudstone landslide with a short sliding distance (approximately 20 m). By simplifying the original site conditions of the landslide, a model slope was built to perform a large-scale shaking table test. The dynamic response of the model was investigated in the time–frequency–energy space using the Hilbert–Huang transform method, and the failure mechanism was clarified from an energy perspective. The Hilbert spectrum indicates that the distribution characteristics of the instantaneous frequency energy are completely different between the loess layer and mudstone layer. Under 0.06 g, large energy is mainly concentrated in a frequency range 10–40 Hz in the loess layer, whereas the energy is mainly concentrated in the 5–10 Hz range in the mudstone layer. This implies that complex reflection and refraction waves occurred in the loess layer. With the increase in intensity, the energy in the loess layer gradually concentrates in the 5–10 Hz range, suggesting that the absorption capacity of the loess layer for high-frequency energy from the relative movement of soil particles increased. The marginal spectra changed from single peak to multipeak with increase in elevation under 0.06 g and changed from multipeak to single peak (with a predominant frequency of approximately 5.6 Hz) with increase in intensity, demonstrating that elevation (>1/2H) can amplify the high-frequency cumulative energy under 0.06 g, showing that input seismic energy gradually takes dominance. Large cumulative energy (10–40 Hz) and instantaneous energy are mainly distributed at the slope shoulder and loess layer. This causes the formation of cracks and a sliding surface in the loess layer. The failure phenomenon of the model slope is close to that of the Buzi landslide, in which sliding occurred at the middle–upper part of the slope within the loess layer.