The evolutive mechanism of debris flows: analysis and protection works

Debris flow analysis requires the choice of a theoretical fluid model. The main models used to describe the mechanics of debris flows are the plastic viscous fluid model, above all the Bingham fluid model, and the dilatant fluid model. The dilatant fluid model is usually applied to analyse the behaviour of flows in which the viscosity of the pore fluid is relatively low and shear rates, mean grain diameter, density and water content are sufficiently high. A 3D numerical model based on the Cellular Automata Method (Deangeli et al., 1994) using the fluid dilatant model proposed by Takahashi has been applied to simulate the evolutive mechanism of debris flows. In recent years great interest have been given to the study of Cellular Automata. In this kind of model the system is subdivided into a set of cells (or sites), each with a finite number of possible values. The values of each cell is simultaneously updated in a sequence of discrete time steps, according to a fixed deterministic rule. The rule at each site depends only on the values of the neighbouring sites. The Cellular Automata model has been applied to back analyse an important debris flow that occurred in Lessolo-Ronchi (Italy), during the flood of November 1994. This study allowed the calibration of the geotechnical parameters of the unstable mass and the setting up of a numerical model to forecast the subsequent travelling of debris flows in the landslide area. The project of protection work was designed and verified on the basis of the numerical model results.