Insights into the kinetic and fragmentation characteristics of a ridge-top rock avalanche based on field investigation and discrete element simulation

The present study provided a preliminary investigation on the kinetic and fragmentation characteristics of the Xuzha rock avalanche, a ridge-top rock avalanche located in the southeast of the Tibetan Plateau, China. Field investigation revealed that the Xuzha rock avalanche originated from a steep slope and caused the tributary of the Jinsha River dammed, showing an extreme high mobility. The vertical profile of avalanche debris showed that it experienced intensive fragmentation during transport. To back-analyze its kinetic and fragmentation processes, the discrete element modeling was conducted. Simulation results suggested that the Xuzha rock avalanche lasted about 80 s and had a maximum velocity of ~ 73 m/s, about 1.5 times the highest average velocity (48 m/s). The travel distance and the thickness of the deposits matched well with the field observations. Notable features including the preservation of the original positional order and the inverse vertical grading of avalanche debris obtained from the simulation were consistent with the field observations. The statistical results of fragments showed that the fragment size distributions could be described by Weibull distribution. In general, with the landslide propagation, the size of fragments gradually decreased and the fragment size distribution became narrower. Further, dynamic fragmentation continuously occurred with the landslide propagation, generating an abundance of fine-grain particles which behaved as interstitial granular fluids between coarse particles. Finally, we inferred that dynamic rock fragmentation and fine particle fluidization were the reasonable explanations for the high mobility of the Xuzha rock avalanche.