Evolution Characteristics and Failure Mechanisms of Retrogressive Loess Landslides: A Case Study from the South Jingyang Platform, China

The South Jingyang Platform, China, is well-known for its continuous irrigation-induced loess landslides. Many scholars have discussed the loess landslides in this area, as the frequent occurrence of these landslides has led to a gradual reduction in the size of the platform. On the basis of these studies, this paper provides an updated summary of the distribution, evolution characteristics, and future trends of these landslides over the past 20 years. It was found that from 2003 to 2023, a total of 76 landslides occurred, mainly concentrated in three areas. In addition to forming retrogressive landslide groups, the large amount of landslide deposits at the substrate also transforms into loess mudflows, causing a disaster chain. The rapid rise of the groundwater level is the main key factor causing these flowslides, and the widely distributed joints, cracks, and caves in the slopes serve as preferential flow channels, actively contributing to the accelerated rise of the groundwater level. This further decreases the stability of the slopes and is also a significant factor promoting the occurrence of landslides. The occurrence of falls and slides is mainly due to the loosening of the slope caused by previous flowslides, which affects the soil structure and triggers the migration of the soil’s critical state. This explains why flowslides occur in the deep saturated zone, while slides and falls often occur in the shallow unsaturated zone in the study area. Since 2015, flowslides have decreased due to changes in irrigation practices and stabilized groundwater levels, confirming the close relationship between flowslide occurrence and groundwater level fluctuations.