Numerical study on the entrainment of bed material into rapid landslides

The entrainment of channel-path material plays an important role during runout of many rapid landslides. Such a mechanism is able to change the mobility of a flow significantly, through rapid changes of the flow volume and rheology. The purpose of this paper is to use mathematical, rheological and constitutive models to analyse the entrainment effect on runout analysis results. After a brief review and classification of some well-established erosion laws, a simple, yet effective, empirical formula for the entrainment rate has been selected, and is implemented in a continuum mechanics-based numerical model. First, some hypothetical examples are used to test the effectiveness of the implemented entrainment process, and to evidence the respective role of entrainment and topography on a flow propagation. Then a back-analysis is presented of the 2000 Tsing Shan event (Hong Kong), where a small volume of 150 m3 of material grew to 1620 m3 because of the strong erosion along the slope. From the results obtained, it emerges that the new model with erosion implemented can provide a useful contribution in describing the consequences of mass movements in which the entrainment process can play a key rol