Abstract: Experimental studies were conducted on fast shear conditions of saturated and dry loess at south Jingyang Plateau Landslide, Shaanxi by employing ring shear apparatus. Test results indicate that: 1)Compared with the dry state loess, the saturated loess significantly reduce the shear strength index under the same test conditions. 2)The saturated with the dry loess retrieved from south of Jingyang have shown strain softening characteristics in quick succession shear conditions, but saturated loess is more significant softening characteristics than the dried loess.3)Under the same conditions of normal stress, shear rate has significant influence to peak intensity for drying and saturated loess, but the peak strength of the soil in pace with the shear velocity variation is different under the two states. The peak intensity of swaturated loess increases with shear rate, and peak intensity of dry loess decreases with increasing shear rate.4)In different aqueous state, shear mechanical characteristics of loess retrieved from south of Jingyang have different variation of the mechanism. Among them, in a continuous shearing process the shear strength of dry loess is mainly dominated by clay particles friction (resistance) force, particle alignment and the shear surface morphology. Compared with the dry loess, the peak shear strength of saturated loess soil is mainly affected by changes in the cohesion of control. Effect of soil water in the body can exacerbate their degree of strain softening and form shear smooth surface morphology, thereby affecting its peak after the shear stress.

Key words: ring shear test, shear strength, shear rate, strain softening, peak intensity, residual strength