Dynamic simulation of the motion of partially-coherent landslides

• Some rock avalanches travel as a semi-coherent mass before turning flowlike
• Existing models poorly predict the impact area of semi-coherent rock avalanches
• A new model that simulates the coherent phase of rock avalanche motion is presented
• The new model assumes the distance before fragmenting can be estimated a-priori.
• The new model provides more realistic predictions of rock avalanche impact area

Rock avalanches are catastrophic landslides that threaten people and property worldwide. The only way to mitigate the hazard posed by these events is to anticipate their impact area and velocity before they occur. Fluid dynamic models are one tool used to perform this kind of analysis. When these models are applied to some rock avalanche case histories, it has been found that the impact area is often over-predicted. This is due to the fact that the models assume that the landslide fluidizes immediately, when in reality the landslide begins as a sliding of a relatively rigid block, which progressively fragments during motion and only gradually turns flow-like. This work details the derivation, implementation, validation and verification of Dan3D Flex, a dynamic model that can simulate the initially rigid phase of rock avalanche motion. This model has been interfaced with an existing equivalent fluid model to allow for all stages of rock avalanche motion to be simulated. Dan3D Flex only requires one additional parameter which can be constrained based on an examination of the pre-failure topography. The back analysis of two rock avalanche case histories is presented to demonstrate the utility of the new model.