Deformation mechanism of Large Deep Loess-mudstone Landslide under the Coupling effect of Loess Collapsibility and Earthquakes: A Case Study of the Yangpo Landslide in Min County, Gansu Province, China

Loess-mudstone landslides have become the most developed type of landslides on the Loess Plateau due to their ‘double-layer heterogeneous’ structure. Currently, there is a lack of research on the deformation and failure mechanisms of loess-mudstone landslides considering the coupling effects of loess collapsibility and seismic activity. This manuscript investigates the spatial structure and deformation characteristics of a large loess-mudstone landslide in Yangpo Village, Min County, Gansu Province, and the deformation characteristics and mechanisms were investigated by combining numerical simulation methods based on the Swell elastic-plastic model. The research results show: the volume of the Yangpo landslide is approximately 4.65 × 10⁶ m³. The development of three layers of sliding zone, sliding zone is mainly developed in the loess and accumulation of body and mudstone junction, the maximum burial depth of 36.0 ~ 37.0 m. During the water saturation process, the loess structure is damaged due to the surface tension of clay particles (t_s) and matric suction (s), resulting in surface cracks and uneven settlement, which can locally evolve into sinkholes. Numerical simulation indicates that under the action of loess collapsibility, the loess-mudstone landslide produces uneven vertical deformation, with the maximum vertical displacement increasing to 0.71 m. Some areas of the loess layer develop plastic damage zones. Under the coupling effect of loess collapsibility and seismic activity, the uneven settlement deformation of the loess continues to increase, with the maximum vertical displacement reaching 3.71 m. loess collapsibility is identified as a key factor in the deformation and failure of loess-mudstone landslides, with seismic activity exacerbating the deformation and failure. The research findings have significant theoretical implications for understanding the deformation characteristics and stability evaluation of large loess-mudstone landslides under the coupling effects of loess collapsibility and seismic activity. The results could provide geological support for disaster prevention and mitigation of loess-mudstone landslides.