Experimental investigation on the interaction between rapid dry gravity-driven debris flow and array of obstacles

Arrays of obstacles are a potentially effective measure to manage a channel landslide run-out deposit. In this research, three kinds of debris sands with different particle sizes, 0.25-0.5 mm, 1-2 mm and 2-5 mm respectively, are investigated in a 4.28-m-long chute with a fixed incline angle of 40 degrees. Structure from motion (SfM) and other novel image analysis techniques are proposed to analyse the deposits' characteristics, including time histories. These allow measuring accurately the run-out distance, width, 3D topography and area of the deposits which are used to assess the effectiveness of the obstacles to manage run-out deposits efficiently. Experimental results reveal that particle size has a significant impact on the final deposition because they effectively behave as three different rheology characteristics: viscous (fine), frictional (medium) and collisional (coarse). The observations show emerging shape properties that are characterised, as well as surprising behaviours when considering time histories such as the non-monotonic area growth in fine, or viscous, landslides. Other phenomena such as airborne particle jets are observed for the coarse particle size, representing a collisional-type flow. In practical terms, the experiments show that when designing protection barriers, a compromise is needed between length, width and depth of deposition and that this can only be decided based on the structure to be protected.