Modelling the evolution of propagation and runout from a gravel–silty clay landslide to a debris flow in Shaziba, southwestern Hubei Province, China.

Numerical modelling, a physically based method, is adopted to obtain an in-depth understanding of the mechanism of sediment-related hazards such as landslides and debris flows. With its ability to address large deformation problems, the particle flow analysis method (the particle flow code or PFC model) can simulate propagation and runout from landslides to debris flows under complex landslide material compositions with a proper rheological model. Hence, this study aims to analyse the kinematic characteristics of a landslide-generated debris flow event in Shaziba, Enshi City, that occurred on June 8, 2020, with the PFC3D numerical model and linear parallel bonding method. To determine the differences among various processes, field surveys, unmanned aerial vehicle (UAV) photography campaigns, and laboratory direct shear tests were conducted to invert the relevant parameters, such as the digital elevation model (DEM) and shear strength, corresponding to the rheological properties of landslide debris flow materials. In dynamic analysis, the velocity, displacement, and characteristics of landslide deposition were considered. The results indicate that the initial landslide stage started with overall acceleration, and the movement of gravel–silty clay materials lasted approximately 733 s with double-peak velocity curves and nonsynchronous displacement. The maximum velocity of the landslide body was 17.5 m/s, and the maximum displacement exceeded 1000 m. The volume of the landslide body was 9.31 × 105 m3. The simulation results agree with the actual landslide volume (1.5 × 106 m3) and morphology of the landslide dam observed in Qingjiang. The study provides detailed information on the recent Shaziba landslide, thereby providing a useful reference for better understanding the dynamics of gravel–silty clay landslides and preventing the potential hazard for remobilisation of the Shaziba landslide. [ABSTRACT FROM AUTHOR]