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°. 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.