Abstract: With the great development of agricultural hydraulic engineering in China, irrigation induces serious landslide disasters at the edge of loess plateaus. As a typical region of loess landslides induced by agricultural irrigation, the Heifangtai plateau in Gansu province has been paid closed attentions in recent years. To investigate the deforming and failure mechanism of loess slope due to infiltration, undisturbed specimens are obtained from the backwall of a typical landslide in Heifangtai and are used to conduct three series of stress-path triaxial tests to simulate the process of slope failures. Through conducting anisotropically consolidated undrained (ACU) tests and saturated dead-load (SDL) tests with increased pore-water pressure, the initiation and failure processes of saturated loess are investigated. Through conducting unsaturated dead-load wetting (UDL) tests, the initiation and failure processes of unsaturated loess are investigated. Based on above results, the mechanism of infiltration-induced loess landslide is elaborated from the aspects of stress paths and microscopic structure of loess. Besides, the typical physico-mechanical properties of loess are analyzed. The results show that the saturated loess has a unique critical state line which reflects the major stress level corresponding to the thickness of the loess; the state boundary line of the loess can be approximated by its critical state line; the soil-water characteristic curves (SWCCs) obtained from the UDL tests are affected by the stress state, showing lower water content at higher stress level.

Key words: landslide, loess, unsaturated soil, stress-path test, critical state, SWCC