This paper presents experimental results of an unconstrained flow of dry sand down an inclined board at small scale, followed at the toe by a horizontal plane on which the sand spreads. The runout length increases with the increase in the volume of the falling sand and the slope angle. In order to identify these characteristics, mass point movement down an inclined board is introduced. If the position of the mass at start is given, it is possible to determine velocity and position of the point at any given time by means of the relationship of the energy loss, however, the mass point modeling, in which the mass point slides down the inclined board and reaches the horizontal plane, does not fully represent the runout length increase with the increase in the slope angle. To get better identification, we improve the mass-point modeling to explain climb-over and collision of particles, which may occur in the sand sliding down the slope.
Reduction or prevention of disaster due to slope failure includes not only mechanical analysis for instability of soil/rock mass but also catastrophic phenomena, such as debris flow and accumulation, which are not yet exhaustively understood (Aaron, J. and Hungr, O., 2016, Stead, D., 2008). The latter consists of movements with a great amount of energy and travelling farther than expected with a normal sliding friction law. Mechanisms involved in these phenomena are still for most part unknown; several theories have been put forward to explain their extended travel distance but at the present time no general agreement has been achieved and there are still many questions to be answered. Since the number of recorded real cases is limited, due to the difficulty in the prediction of these catastrophic phenomena, several authors have resorted to laboratory tests (Ishimaru, M., and Kawai, T., 2008). Experiments usually reproduce idealized conditions and results are used not only in numerical models validation but also to better understand the propagation mechanisms and to identify parameters influencing velocity and deposit characteristics. Despite the difficulty in matching the scaling laws, the use of a physical model enables studying the influence of each parameter of interest, by controlling and changing one at a time, with known and consistent experimental conditions. In addition several dimensional studies have arrived to the conclusion that with the exception of some particular phenomena, granular avalanches at small scale should realistically reproduce major features of large-scale soil/rock mass movement.