Investigation of the characteristics and long-runout movement mechanisms of the Luanshibao landslide on the eastern margin of the Qinghai-Tibet Plateau

The Luanshibao (LSB) ancient landslide is a typical long-runout landslide that occurred on the eastern margin of the Qinghai-Tibet Plateau. To examine the long-runout mechanism of the LSB landslide, a detailed field investigation and a series of saturated soil triaxial and ring shear tests were carried out. The field investigation results revealed that the flat and broad Maoyaba (MYB) basin provides the required topographic conditions for the long-runout movement of the LSB landslide. The shallow deposit of the MYB basin is mainly composed of saturated weathered granite sand, which plays a key role in resulting in the high mobility of landslides. The results of the triaxial tests reveal that the soils show the characteristics of shear contraction first and then dilatation under static loading, and cyclic mobility occurs under cyclic loading. The results of the ring shear test reveal that the pore water pressure of the sample has undergone three stages of increase-decrease-increase. Finally, the pore-water pressure ratio increases to a constant of approximately 0.79, and the shear resistance decreases significantly. Grain crushing results in pore-water pressure generation and the liquefaction of saturated weathered granite sand for long shear displacement. It is proposed that sliding surface liquefaction is the main reason for the formation of complex surface landforms and the long-runout movement of LSB landslides.