The influence of the bed entrainment-induced rheology and topography changes on the propagation of flow-like landslides: a numerical investigation

Bed entrainment changes the rheology of the sliding mass and the topography of the sliding surface, finally influencing the propagation of flow-like landslides. In previous studies, both empirical methods and physically based methods have been used to simulate bed entrainment. However, the influences of bed entrainment on the rheology and topography of flow-like landslides were not deeply explored. In this paper, the physically based model proposed by Fraccarollo and Capart (J Fluid Mech 461:183-228, 2002) is adopted to calculate the bed entrainment rate, and a new method is proposed to consider the rheology change associated with bed entrainment in flow-like landslides. The new rheology change method and the Fraccarollo and Capart model are incorporated into a quasi-3D finite difference code to analyze an ideal case and two typical flow-like landslides. The two real landslides are the Dabaozi landslide and the Dagou landslide in the Chinese Loess Plateau. They represent two different bed entrainment scenarios: the erodible mass is relatively thick in the Dabaozi landslide, while that of the Dagou landslide is relatively thin. The results show that both the topography and rheology changes have a significant influence on the propagation of flow-like landslides: (1) the rheology change mainly influences the run-out distance of a landslide, while the topography change mainly impacts the lateral spreading; (2) entraining soft materials can significantly increase the run-out distance of a flow-like landslide; (3) the topography change can obviously constrain the lateral spreading of those landslides when the erodible mass is relatively thick. In addition, it shows that the rheology change and topography change influence each other in the propagation of a flow-like landslide, and the proposed rheology change method in this paper can properly reflect this interactive process.