Developing a standard methodology to characterize and modeling debris flows

Debris flows affect frequently the mountain regions and, because of their speed and destructive force, threaten roads, buildings and human lives. The reconstruction of debris flows paths has long been studied and several simulation models have been implemented, but a believable scenario can be obtained only by resorting to real parameters, suitable to characterize the involved material. The research presented in the paper is aimed at individuating a standard methodology that from field survey, through different laboratory analysis, comes to the assignment of numerical values to the basic parameters of the debris flow simulations (yield stress and viscosity). After obtaining these values, simulations were performed to validate the methodology. To this purpose a basin sited in the Northeast Italy has been studied and sampled. The chosen test site is located in the Val Canale valley already involved, since 2003, in at least three alluvial events. The present project started with a sampling phase. In order to ensure the representativeness of the sample, it is important to identify significant collection points, in the source, transport and depositional areas, and to collect a huge quantity of heterogeneous material. In the laboratory samples were subjected to grain-size, mineralogical and rheological analysis. Suspensions of the fine fractions were prepared at equal solids concentration and studied using a controlled stress rheometer. Different experimental methods were proved to individuate an appropriate methodology suitable to characterize the plastic behavior of the fine particle suspensions derived from the different sampling points. With the range of values obtained, numerical simulations, using FLO-2D software, were performed in order to verify the consistency of the parameters and their representativeness even if a back analysis is not available.