Slope disasters inducing stony]type flow are occurring more frequently due to ongoing global climate changes, but the mechanisms of granular flow have not been thoroughly explained. The mechanism of dry granular flow was examined in micro and macro views. First, flow behaviors of dry granular materials on a slope were examined using PIV image analysis and a discrete element method in two dimensions. The simulation results replicated the tendencies shown in the test model results. Relationships exist between macro and micro behaviors during phenomena such as velocity distributions in depth stratification and uplifts of large particles that change flow gradings. Similarly, stress chains which are transmission paths of contact forces, are focused. The distribution of the averaged coordination number was found to correspond to the distribution of velocity, indicating three layers of structure. This stratification could be explained by the state parameter, a relative variable dependent on void ratio, mean normal stress, and critical state. Moreover, the stress chains formed from the riverbed concentrated the larger particles and pushed them upwards towards the flow surface.

Key wordsFdiscrete element method, critical state, stress chain, changing grading, uplift of large particle