Experimental evidence from the triggering of debris flow along a granular slope

The instability of a granular slope, with seepage flow and low tail downstream water level, has been experimentally investigated to point out the conditions associated to the formation of a debris flow, excluding the case of the debris flow triggered by a failure due to the toe erosion. The materials employed in the experiments are uniform glass spheres (d = 0.003 m) and two different gravel (d50 = 0.007 m and d50 = 0.0022 m). Experimental runs show that the triggering of debris flow is due to the overland flow.