A fluidized landslide occurred in the Loess Plateau: A study on loess landslide in South Jingyang tableland

The South Jingyang tableland is located on the southern Loess Plateau of China. Ever since the introduction of the water division project in the 1970s, more than 40 loess landslides have occurred in this tableland-terrace slope topography here. On the morning of March 8, 2016, a loess landslide induced by irrigation occurred in Jiangliu Village on the South Jingyang tableland, and around 20,000 m3 of loess rapidly slid along a 65-m high slope for 260 m. The moisture content of the slip mass displayed a dramatic change along the slip direction: the water saturation degree in the landslide depression was relatively high, and the leading edge was in a flow state; there were some local natural sub-areas, but the overall area showed a characteristic fluidized. A field investigation indicated that while macropores developed in the loess and deep joints provided a preferential passage for the infiltration of irrigation water, which became a major water source for the slip mass, the softening of the toe part of the slope caused by irrigation became the major factor resulting in the instability of the slip mass. Undrained triaxial shear tests on loess in natural water content and fully saturated state show that the enhanced saturation degree not only lowered the soil mass strength but also increased pore water pressure, resulting in the zoning status of the Jiangliu landslide. The angle of reach formed during this landslide was approximately 14°, which demonstrated motion characteristics of long-runout. Further, considering the standing water at the slope foot and unique properties of slip soils after the landslide occurred, it is speculated that the motion mechanism of this high-speed and long-runout landslide was associated with loess liquefaction that led to sharp decrease in shear strength of the displaced landslide materials during the shear process.