ABSTRACT
Debris flows and mud flows are phenomena of very intense sediment transport, affecting the mountain streams in particular hydrological conditions. They are often sudden phenomena, that have caused lots of catastrophic damages with human losses during last decades, to such an extent that the research is turning to a better understanding of the mechanism of these hyper-concentrated flows (Armanini, Fraccarollo et al. 2005), (Takahashi 1981), ( Takahashi 1991). New rational approaches, more convincing from a physical point of view, are necessary in order to predict such events and to properly design efficient protection measures to a smarter defence strategy of such kind of geophysical phenomena and to map the areas at risk. The first empirical approaches were more or less qualitative descriptions and classifications without any physical basis. In fact there is a great number of classifications that require a priori knowledge of the flow features, but this kind of information
the presence of cohesive (clayish) particles in the flow, the solid phase is composed by particles with size bigger than fine sand and can be treated as a granular fluid. Under the hypothesis that the particles dimensions are much smaller than the control volume and that this volume is infinitesimal, the particles could be liken to a fluid with an own rheological law, which describes the interaction mechanism among the grains. Bagnold (1954) proposed the first theory for granular fluids. He distinguished two flow regimes, on the base of the relative importance of stresses due to inertia and stresses due to viscosity. His pioneering work inspired most of the formulations utilized until now and was refined by the introduction of kinetic theory proposed by Savage & Jeffrey (1981) and Jenkins & Savage (1983). This approach derived from the analogy with the kinetic theory of gases, pursuing the idea of deriving a set of continuum equations (mass, momentum and energy conservation) entirely from microscopic models of individual particle interactions. This theory can be employed to obtain a solution for the flow in terms of distribution of concentration, velocity and velocity fluctuations (granular temperature). However it was derived on the basis of some simplified hypothesis, which have to be improved and generalized in order to successfully apply kinetic theory to debris flow.
