The kinematic characterization of a rockfall in Zagunao Valley in the eastern margin of the Tibetan Plateau

On June 28th, 2020, during the rainy season, a rockfall occurred at Sima Village in Zagunao Valley on the eastern margin of the Tibetan Plateau. The kinematic characteristics of rockfall were studied through a detailed field investigation, video frame analysis, and numerical simulation. The motion process of a flat boulder with a volume of 56 m 3 was recorded by a mobile phone camera, and the video provides critical information for tracking and analyzing the motion of the boulder. The results show that the failure mode was a sliding controlled by three sets of structural planes on the slope. The entire motion process of the flat boulder is characterized by bouncing, rolling, river-crossing, and halting stages, respectively. The video of the flat boulder shows its rotational motion along the minor axis, much like a rolling wheel. The numerical simulation indicates that the potential threat section of Xuemeng Road at Sima Village was about 260 m. For the boulders that passed the threat section along the road, the maximum velocity was 26.8 m/s, the maximum kinetic energy was 7.3 × 10 4 kJ, and the maximum jump height was 6.7 m. The kinetic energy and jump height analyses provide essential parameters for protective design. In addition to active and passive protection measurements for mitigating future events in the Sima rockfall zone, drainage measures in the upper catchment area would effectively reduce the erosion effect of slope runoff on gullies.