Experimental case study of seismically induced loess liquefaction and landslide

Abstract

The 1920 Haiyuan Ms 8.5 earthquake induced a large number of fluidized loess landslides in China, characterized by low slope angles, long run-out distances, and fluidized movement. The mechanism of these landslides has aroused considerable interest, although additional research is needed to understand more fully the behavior of the loess and the failure mechanism. Field investigation was conducted on the Shibeiyuan landslide, and loess samples collected for later laboratory analysis by conventional geotechnical tests, triaxial compression tests, and ring shear tests. The field survey revealed that the Shibeiyuan landslide occurred on a concave slope (<5°) with a long run-out distance, indicating a small apparent friction angle. It was also found that standing water was present in the landslide area and that the loess had high porosity. Experimental results showed that application of cyclic shear stress to a loose and saturated loess specimen causes excess pore pressure to develop gradually, resulting in a decrease of effective stress until liquefaction. The steady state strength of the loess showed no correlation with stress path, but it was closely related to the degree of saturation, loading rate, and void ratio. This indicates that excess pore pressure can accumulate under seismic loading and that plastic deformation can develop rapidly within a shearing zone, resulting in loess liquefaction and a reduction of shear strength. In the Shibeiyuan landslide, the steady state strength was near zero with the large deformation related to the low angle, long distance, and fluidized movement.