Numerical investigation of reverse segregation in debris flows by DEM

Studies of the mechanisms and the effects on the flowing mobility for hazardous geophysical flows (e.g., debris flows) is crucial for hazard mitigation and prediction. Granular flows with grains of mixed sizes are numerically modeled and the contact behavior of solid particles is fundamentally studied using the discrete element method. The mechanical effects of particle contacts (shearing and collision) are contrasted with geometrical effects (kinetic sieving) to explain the mechanism of reverse segregation. Compared to granular flows with uniform solid particles, the effect of segregation on granular flowing mobility is investigated. It is found that reverse segregation can significantly influence the flowing mobility and the flowing regimes in the front head of the granular body. A mechanical explanation of the segregation mechanism can be presented by a new dimensionless number, which is correlated with the contact force.