A comparative assessment of rheological laws for mud flows

Extreme events with intense and prolonged rainfall have been increasingly frequent along the last decades due to the ongoing climate change. As a matter of fact, devastating landslides have caused huge damages, both in terms of human lives and economic losses. Among those phenomena, slurry flows, occurring along natural streams on mountain slopes after long or intense rainfalls, are very dangerous landslides. On 15-16 December 1999, a series of destructive slurry flows hit the residential area of Cervinara in Campania, Italy, which developed from the liquefaction of the pyroclastic soils covering the carbonate bedrocks. Several authors have back-analysed these events based on the approximation of the mixture as a continuous equivalent fluid. For this class of models, depth-averaged approaches are considered a convenient trade-off between model descriptive capabilities and model complexity. In this approach, both internal and basal flow resistance are described by the bottom shear stress. This work indagates the different rheology models applied for the Cervinara 1999 events. At first, the landslide propagation has been modelled with a modified Voellmy law, consisting in a frictional component and a turbulence parameter (1). Assuming laminar flow conditions, a non-frictional rheology with bottom shear stress τ, expressed in terms of consistency K and yield shear stress τy has been described with a modified Bingham law (2). Another frictional rheology has been represented as a Coulomb-like law depending on basal friction angle