Formation mechanism analysis of irrigation-induced retrogressive loess landslides

Abstract

The Loess Plateau covers about 6.6% of the total land area of China. Landslides are serious concerns in Loess Plateau of China, and the south Jingyang tableland on the Loess Plateau of China has received significant attention because of frequent occurrence of gradual retrogressive loess landslides (GRLL) there. However, the characteristics and mechanism of GRLL are largely unknown. In this study, three typical landslide groups, namely, Miaodian-zaitou landslide group, Jiangliu landslide group and Dabuzi landslide group are chosen as examples to analyze the characteristics of GRLL by performing a field survey and undrained triaxial shear tests. Loess fissures are found to play a key role in controlling the evolution of landslides. On the one hand, the mechanical properties of loess surrounding fissures rapidly weaken due to water infiltration into loess fissures. On the other hand, the self-weight of the overlying loess increases since water infiltrates into fissures. The undrained triaxial shear tests results indicate that loess specimen shows either strain-hardening or strain-softening behavior, depending on its initial moisture content. Furthermore, reduction in the shear strength of loess samples is observed as moisture content increases. Three factors associated with the characteristics and mechanism of GRLL group, including strata lithology, slope shape, irrigation and rainfall are discussed. Finally, the formation mechanism and evolution of GRLL are summarized into three stages, namely, a creep-tensional stage, a localized liquefaction stage and a sliding stage. This study provides important insights on gradual retrogressive characteristics of loess landslides and facilitates appropriate safeguards to reduce the risk of such landslide hazards.