Interaction between landsliding materials and the underlying erodible bed in a loess flowslide

Loess landslides exhibit strong interactions with the terrace sediments of the Jing River on the South Jingyang Platform, Jingyang, Xi'an, China. Analysis of past landslide events revealed that the sand layer of this terrace was thrust up to the surface, accompanied by other terrace sediments of carrying. This led to the formation of a thrust nappe structure over a long distance. We performed ring shear tests to examine the shear behavior of this sand layer, with the finding that saturated sand was highly susceptible to liquefaction-induced failure. The groundwater level of the study area is high, resulting in near-saturation of the sand layer. Therefore, topographic interferences contributed additional variables and increased interaction complexities. Simulations indicated that the liquefied sand layer was compressed and forced. Due to the absence of constraints, the sand layer near the bottom of the slope was sheared out over a relatively short distance. On the other hand, particle interia and constraints of the stable layer resulted in the sand layer near the distal part of the deposits being sheared upward to the ground. Finally, an initiation-movement model of loess flowslides is proposed. It describes static liquefaction of the loess layer of the slope resulted in occurrence of flowslides. Collisions between the deposits from the platform edge slope and terrace sediments resulted in the shear liquefaction of sands. The landslide experienced four stages as they moved: scraping collisions, floating scrapes, folded thrusts, and nappe accumulation.