Preliminary investigation of hummocky landforms and hypermobility of the Bingda landslide, northeastern Tibetan Plateau

Lianji Liang ^* Fuchu Dai ^* Yuxuan Zhu Rongshen Pan

• Beijing University of Technology, Beijing, China

Rapid and long-runout landslides characterized by their high speed, long distance mobility, huge capacity and volume, would pose significant threats to infrastructure and life safety. In this study, a rapid and long-runout landslide occurred in the Bingda village of the northeastern Tibetan Plateau, which was triggered by heavy rainfall in June 2017 was preliminarily investigated. On the basis of detailed field surveys, high-resolution satellite imagery analysis and laboratory tests, the morphological and sedimentological features of the landslide were described, and the formation mechanism of hummocky landforms and its insight into the extraordinary movement of the Bingda landslide was deduced. The field investigation and satellite imagery analysis showed that there were nearly 200 hummocks, mostly with normal circular basis and the height of ~0.1 m-7.5 m, distributed in the transfer and accumulation areas of the landslide. The height and number density of hummocks decreased away from the transfer area to accumulation area, and displayed higher heights at the outer bends of the gully channel than that at the inner bends of it. The characteristics of spatial distribution and the composition of hummocks indicated that significant generation and dissipation of pore-water pressure within the loose and saturated silty clay layer in the runout path was the most probable reason for the formation of hummocky landforms. This study also provided the insights into the hypermobility mechanisms of Bingda landslide, suggesting that this landslide began with the sliding failure of the weathered colluvium in the source area, then the landslide debris travelled into the channel and impacted sudden undrained loading and rapid shearing to the underlying silty clay layers in the gully. These processes generated the pore-water pressure and reduced the effective stress within the soil particles, resulting in the decrease of the frictional resistance in the substrate, finally facilitating the rapid and long-runout movement of the landslide.