Effect of Particle Size Segregation in Debris Flow Deposition: A Preliminary Study

Abstract

To understand the effect of size segregation in the depositional process of debris flows, both flume experiments at the laboratory scale and numerical simulations using the discrete element method (DEM) are performed. A variety of particle size distributions with coarse and fine particles are adopted. It is found that larger particles tend to reach the front of the final deposits, while small particles are accumulated at the tail of the flows. Quantitative agreement is achieved in the DEM simulations, where rolling resistance and geometric roughness at boundaries are adopted to account for the effect of particle shape. With the DEM results, the effect of segregation on the runout distance is studied from the perspective of energy dissipation. The progress of segregation is analyzed in detail, which revealed that segregation occur slowly while the flow is propagating rapidly over the slopes; it becomes significant during the deposition stage, where more large particles are found near the surface. The effect of segregation in debris flow deposition can help better predict the runout distance and impact pressure, which is crucial in the assessment and mitigation of debris flow-related natural hazards.