Numerical modeling of a debris flow event occurred in Campania region, southern Italy: consideration on the rheological model parameters on the run-out

In the past, the most widely used model for the analysis of rapid landslides and similar phenomena has been the so-called “lumped mass” model, i.e. a model based on the dynamics of a rigid block sliding over an inclined plane. In recent years, the “lumped mass” model has been put aside in favour of more complex numerical models based on the continuum mechanics theory. The theories set to the continuum are able to describe both the evolution of a limited granular mass and the velocity distribution associated with a landslide on an inclined surface, applying the De Saint Venant equations to the analysis of the granular mass run-out. One of the most critical aspects of such a model is the choice of a representative and adequate constitutive model for the granular-fluid mixture. In order to analyze this aspect, we referred to the catastrophic debris flow event of Pozzano (Napoli), occurred in 1997, which is extensively documented in literature. We applied the two-dimensional code DAN –W (largely used in back analysis of debris flows occurred in Campania region). The constitutive model used is the Bingham ones with three different pair of parameters for the yield stress and Bingham viscosity. The numerical model was then used in order to highlight the differences between the numerical results with the three pairs of parameters adopted on the base of extensive laboratory investigation (e.g., model A), in situ observations (e.g., model B) and a hybrid procedure proposed (e.g., model C). The proposed procedure try to take into account the scale effect between the laboratory experiments (model) and the real events (prototype).