Abstract: Agricultural irrigation on Heifangtai loess plateau has triggered dozens of loess earth flows. In this paper, IKONOS image was first used to interpret the topographic features of those earth flows, complimented with a detailed field-walk survey. The results indicated that loess earth flows had a travel distance of over 300m, constituting the most destructive threat. The failed material was deposited in a flow-like lobe form. The elevation of the underlying impermeable clay was measured from the outcrops and boreholes, indicating that the eastern part of the plateau was lower than the west. It was observed from groundwater flow modeling that groundwater flow was controlled by the topography of underlying impermeable clay, and converged and partially discharged in the east margin of Heifangtai. This is in coincident with the phenomena that most loess earth flows occurred in the east margin. Laboratory stress path tests were then performed on undisturbed specimens to explain the failure mechanism of loess. The test results show that the initiation of loess earth flow is probably triggered by static liquefaction resulting from rise of groundwater table

Key words: loess earth flow/landslide, agricultural irrigation, groundwater flow modeling, laboratory tests, Heifangtai