The Shibeiyuan landslide is a typically large loess flow slide which was triggered by Haiyuan earthquake in 1920. Understanding its behavior and mechanism is very important to study liquefied slope failures with long travel distance in the loess area. The in-situ investigation of the Shibeiyuan landslide shows that the saturated loess or the loess with high water content has high liquefaction and destructive potential which could cause liquefaction or flow slide under strong earthquake. The dynamic triaxial shear tests are performed on seven intact soil specimens taken from three places at the landslide. In addition

the scanning electron microscope (SEM) microscopic characteristics of the soil specimens are used to clarify the shear behaviors of these soil specimens. According to the results

the relation between water pore pressure and strain

as well as the relations between liquefied stress ratio and particle size

microstructure parameter

and degree of saturation are analyzed. The analytical results reveal that the liquefied stress ratio decreases and pore pressure response is stronger with the increasing of clay content. Meanwhile

the specimens with greater porosity have greater fractal dimension and less liquefied stress ratio. Moreover

the liquefied specimens are denser and its fractal dimension is greater compared to that before the liquefaction. Additionally

the degree of saturation has great influence on the state of interparticle cement and the microstructure in loess. The saturating process shows that the ionic concentration of the pore water is greater and the rupture of the interparticle contacts is easier when the degree of saturation becomes greater. As a result

the structural strength of the specimens decreases

leading to the decrease of the liquefaction stress ratio.