Study On The Motion Mechanism Of High-speed Remote Loess Landslides At South Jingyang Plateau

China has the broad distribution of loess, and in the northwest loess area accounts for more than 70% of the national distribution of loess area. Because of the unique topography characteristics and engineering properties of loess, loess landslides happen frequently, which are very dangerous and severely restrict the economic and social development in loess area. High-speed remote loess landslide is a special type of loess landslides, with the characteristics of high sliding speed, long distance, large energy, strong impact force and happens suddenly, it caused massive destruction and losses. Based on systematically summarizing the research dynamic of high-speed remote landslides, this paper took the high-speed remote loess landslides at south Jingyang plateau for example, through the on-site investigation, collecting and collating the relevant literature, the geological environment background of the study area and the distribution and motion characteristics of the high-speed remote loess landslides at south Jingyang plateau were analyzed. Based on the research about the physical and mechanical properties of the Q2 loess of the study area in laboratory, using the UDEC numerical software to simulate the movement of the high-speed remote loess landslide, the motion mechanism of high-speed remote loss landslides at south Jingyang plateau was discussed, the research results have important significance for the mechanism analysis and countermeasures of high-speed remote loess landslides. The main research contents and conclusions are as follows:(1) On-site investigation suggests that there are 26 high-speed remote loess landslides in 22 places being identified in the study area. Landslides show zonal distribution along the plateau edge, mostly form landslide group. Landslides are affected by rainfall and irrigation significantly.(2) CTC(Conventional Triaxial Compression Test) suggests that in study area, the stress- strain curves of saturated Q2 loess show “strain softening” feature. The peak strength and the residual strength of the soil increase with the rising of confining pressure, and the difference between peak strength and residual strength increases too. Besides, the peak strain and pore water pressure of the soil also increase with the rising of confining pressure.(3) Ring shear test suggests that in study area, the shear strength of saturated silt increases with the increase of normal stress at the same shear rate. At different share rate, the shear stress–displacement curve shows “strain softening” feature at low normal stress while shows “strain hardening” feature at high normal stress. At same normal stress, the residual strength of saturated silt decreases with the increase of shear rate, and it decreases greater when the normal stress is bigger.(4) The numerical simulation results based on UDEC suggest that: the high-speed remote landslides at south Jingyang plateau are pull-type landslides, and the sliding process finished in a short time. The landslide reaches to the maximum speed in a very short time once it happens, then it slides at a relatively high speed on level terrace of Ching River. In the sliding process, the back of the landslide has a lower speed and stops early, the front of the landslide moves fast and has a long displacement, which forms a thin layer on the terrace when it stops.(5) The motion mechanism of high-speed remote loss landslides at south Jingyang plateau was that: when the landslide happens, the shear strength of the soil reduces sharply and releases tremendous energy, besides, the gravitational potential energy of the sliding mass partially or fully converted into kinetic energy, which leads the sliding mass moves in a high speed. During the sliding process, the friction resistance decreases and even complete loss because of liquefaction, which generates a long sliding distance eventually.