Morphology and Substrate Control on the Dynamics of Flowlike Landslides

A numerical model set up to simulate rapid flowlike landslide motion across three-dimensional terrain has been used to investigate the capability of various constitutive relationships to model the dynamics of complex events characterized by a changing type of substrate and morphology (e.g., glacier, bends). The numerical procedure is based on a continuum mechanics approach and on depth-averaged St. Venant equations for shallow flows. The developed RASH3D code includes the possibility of using several rheological laws, whose parameter values can vary along the runout path. Two rock avalanche cases, with some morphological peculiarities along the propagation path, have been numerically back-analyzed with both a frictional and a Voellmy rheology. Of the two considered rheologies, the Voellmy model produces the most consistent results in terms of runout area as well as velocity values. The main drawbacks of the frictional model are the tendency to predict excessive spreading of the mass and to overestimate the velocities. The results show that, when a complex problem of runout of rapid flowlike landslides has to be analyzed, it is necessary to have detailed knowledge of the geological and morphological features and to resort to increasingly complex rheologies.