Initiation mechanism of mudflow-like loess landslide induced by the combined effect of earthquakes and rainfall

The events of landslides induced by the combined effect of earthquakes and rainfall are more dangerous than those induced by earthquake or rainfall. The Yongguang loess landslide induced by the Minxian–Zhangxian Ms 6.6 earthquake in 2013 is a typical example of a landslide induced by the combined effect of an earthquake and rainfall. A few scholars have carried out relevant research on this landslide, but the initiation mechanism of this kind of landslide has not been elucidated. Therefore, the initiation mechanism of loess landslide under the combined effect of earthquakes and rainfall is studied through indoor geotechnical tests, shaking table slope model tests and numerical simulations. The indoor geotechnical tests show that the mechanical properties of Q3 loess would change significantly (the mechanical strength would decrease sharply) when soaked in water and that its strength would be further lowered under dynamic action. The slope model test results show that the infiltration depth at the slope top is deeper than that of the slope surface after continuous heavy artificial rainfall and that the natural frequency of the shoulder of the front edge of the slope top is closer to the frequency of the loading wave than it is in other parts of the slope; so the amplification effect of the seismic ground motion at the shoulder of the front edge of the slope top is more significant and the soil damage is more serious under seismic dynamic action. With the rapid increase in the residual deformation and pore water pressure of the soil mass, the loess properties change substantially, that is, loess liquefaction occurs when the pore water pressure and residual deformation reach a certain threshold. Under the action of the subsequent seismic ground motion, the liquefied loess mass of the front edge of the slope top rushes out along the sliding bed and slides down the slope surface in the form of a loess mudflow; that is, a mudflow-like loess landslide is induced. A simplified mechanical model is used in the numerical simulation test and can reproduce the triggering process of this kind of loess landslide. In this research, the initiation mechanism of mudflow-like loess landslide induced by the combined effect of earthquakes and rainfall is revealed by comprehensively considering a variety of test results, and a sliding distance calculation formula is proposed, providing a foundation for the prevention and control of this kind of landslide disaster.