SIMULATION OF PROPAGATION PROCESS FOR THE DABAOZI RAPID LONG RUN-OUT LOESS LANDSLIDE IN THE SOUTH BANK OF THE JINGHE RIVER, SHAANXI PROVINCE

Rapid long run-out landslide usually moves in high speed and travels for a long distance, therefore it trends to cause catastrophic effects on its overlong travelling path. In the study area of the Jingyang south loess tableland in this paper, this kind of landslide occurred frequently in last few decades and resulted in serious disasters. Since the destructive properties of this kind of landslide, to study its moving process and mechanism is necessary and of great significance for both study and construction purpose. Spatial prediction is a sort of effective methods to prevent landslide hazards. To make spatial prediction for rapid long run-out landslides accurately, making back analysis of the previous events is indispensable. For above reasons, this article choose a typical rapid long run-out loess landslide named "Dabaozi" in the south bank of Jinghe river, Shanxi, as study target to simulate its moving process and analyze its moving mechanism. Detailed field surveying was conducted, which reveals the landslide's matter source is mainly made up of loess stratum from L₁ to L₉ in the slope and sand gravel in terrace in front of the slope. Sand gravel layer was apparently entrained by the original loess landslide mass which is shown by the over-thrust of sand gravel in the front of the landslide, so it was regarded as potential landslide mass in order to take entrainment into account in building the Digital Elevation Model (DEM) of the landslide and simulation. In addition, 2groups of undisturbed loess and sand gravel samples were taken from the landslide area to conduct consolidated undrained (CU) triaxial tests and ring shear tests and some common indoor tests to get the physical and mechanical parameters needed in the simulation. On this basis, we utilized a software LS-RAPID which is developed from Sassa's geotechnical model to study the kinematic behaviors of this landslide. As a results, the moving speed, travelling path, thick of deposition mass and some other important kinematic indexes of the landslide were obtained. The simulation results show that the max average velocity of the landslide is about 9.56m·s^-1 when it has moved 5.7s, and the whole moving process lasts about 24.5 seconds, and the topography obtained by simulation shows good accordance with fact in respect of the travelling distance and depositional forms. The moving process can be divided into two stage according to the transformation of motion state based on average velocity obtained from simulation, one is the starting accelerated stage (0s-5s) which has an acceleration of 1.68m·s^-2, the other one is the moving decelerated stage which has an acceleration of -0.51m·s^-2, and the topography of simulation shows that the transformation occurs when the whole landslide mass just reaches the terrace in front of the slope. By summarizing, we find that the initial steep topography condition in the study area and Q₂ loess's high constructive strength play pivotal roles in making the landslide moves fast, and the landslide surface liquefaction occurred in the horizon terrace which mainly makes up of saturated sand-gravel contributes to a long travel distance, and this article can provide beneficial reference to the later study of loess rapid long run-out landslide.