Numerical simulations of debris flow events provide a useful tool for investigating, within realistic geological contexts, the dynamics of these phenomena. One application of such numerical models is to evaluate and forecast impact loading on protection barriers. Most of these models are uncoupled methods: this means that it is necessary to use different codes for analysing the motion phase and for evaluating impact forces. In this way, the uncertainties related to the barrier design are increased and difficult to quantify. In this paper the combined finite-discrete element method, FEMDEM is employed to back-analyse experimental impact tests of debris flow interacting against rigid and waterproof barrier. This methodology allows the simultaneous determination of flow characteristics (velocity and thickness) and impact load on the barrier structure. Two different numerical set-ups were adopted to reproduce laboratory experiments. In the first case, we defined a priori the size and the shape of the impacting particles. In the second case, the unstable mass was hypothesised as a unique block with fracture joint elements behaviour, cohesionless, and very low tensile strength. In this way the gravity and friction forces led the particles flowing into the flume. The results were compared in order to quantify the effects of the set-up schemes and material characteristics on the simulations. Limitations and future developments on the application of FEMDEM methodology to this type of geotechnical problem are discussed.
Forecasting debris flow motion characteristics and impact loads on obstacles is an essential component of landslide risk assessment, but it is still a big challenge. The runout prediction provides a mean of defining the susceptible areas, estimating the debris flows intensity and working out the information for the individuation and design of appropriate protective measures (Pirulli and Sorbino, 2008). Concerning the evaluation of debris flow motion characteristics, numerical simulations can provide a useful tool. In the attempt of modelling landslide dynamics, many methods based on continuum (Savage and Hutter, 1989; Hungr, 1995; Pirulli, 2005; Pastor et al., 2009) or discontinuum (Will and Konietzky, 1998; Richefeu et al., 2012) mechanics have been developed. The outputs of these models are fundamental for the design of countermeasures and they are used as inputs in codes (e.g Brighenti, Segalini, and Ferrero, 2013; Hungr and Kellerhals, 1984) for evaluating impact forces on structures.