A rainfall model test for investigating the initiation mechanism of the catastrophic loess landslide in Baqiao, Xi’an, China

Due to the significant decrease in strength of loess after encountering water, loess landslides induced by rainfall are very catastrophic and widely distributed in the Chinese Loess Plateau. On September 17, 2011, a catastrophic loess landslide induced by rainfall occurred in Baqiao district, Xi'an, Shaanxi Province, China, resulting in 32 casualties and bringing great fear to the local residents. This landslide event was characterized by three individual landslides. Field investigations, geological exploration and model experiments were conducted to reveal its initiation and movement mechanisms. The results show that 1) Multiple groups of fissures in the ring-cut adits were found at a location 3 m inward from the slope surface. The minimum opening width of these fissures is 0.5 cm, and the maximum is 4 cm. The fissures develop nearly vertically and have good extensibility and connectivity. 2) the whole process of rainfall-induced landslides can be divided into 3 stages: rainfall infiltration and weight increase; crack expansion and slope deformation; slope collapse and creep deformation. 3) The volumetric water content, pore water pressure and vertical stress variation of the soil in our model all increase first and then decrease. Specifically, these three parameters increase slowly during the pretest and stabilization periods and increase fast shortly before the landslide occurrence. The volumetric water content of the soil on the side containing joints increases faster, verifying that the joints act as preferential channels that accelerate rainwater infiltration. The results of the study provide an important scientific foundation for future research on rainfall-induced loess landslides and their deep-seated mechanisms, and fill the gaps in research related to large-scale physical modeling experiments.