Three-Dimensional Numerical Simulation Of Yigong Rock Avalanche Using Particle Flow Code

A catastrophic rock avalanche took place in Yigong Village, Bomi County, Tibet, on April 9,2000. Based on the real DEM elevation data and characteristics of geological structure of the rock avalanche, a three-dimensional numerical model was established using particle flow code. The whole evolution of the rock avalanche, including its trigger, propagation, and deposition, was reproduced. The duration, mean velocity, energy dissipation, and the morphology of the deposit were analyzed. The main conclusions are as following:(1)A total duration was about 300 s. The rock avalanche moved at a highest velocity of 53m/s at 30 s. At the early stage of the movement, the rock avalanche was triggered due to the fissured water, and the velocity increased linearly. When the mass moved in the gully of Zhamunong, its velocity decreased and came to rest eventually.(2) The mass front of the rock avalanche always moved at a high velocity during its propagation. The higher initial elevation of the mass front was, the higher maximum velocity it could reach.Different from the leading edge, the speed of the trailing edge of the landslide debris flow increased linearly at the initial stage. When the velocity of the landslide trailing edge reached the maximum value, it rapidly decline because of the the impact of topography. At the same time, the maximum speed of sliding surface of the sliding mass can reach 90m/s, far greater than the middle and the bottom surface which is 60m/s. However, the running time of the sliding surface is much more less.(3) There is an enormous energy accumulation within the mass of Tibet Yigong rock avalanche, which can be up to 1×1015J. Because of the mutual impact between topography, and the sliding body, the interior of the sliding body, the unbalanced force between the particles in the sliding mass is increasing, and the sliding mass is seriously debrised, the landslide then shows fluid characteristics.(4) After the sliding mass of Tibet Yigong rock avalanche runs out of ravine, the sliding mass then is not subjected to the constraints of both sides of the mountain terrain, and deposits on both sides spread. Eventually the deposits form fan-shaped accumulation.