A general frictional-collisional model for dense granular flows

Landslides can often be treated as dense granular flows that are characterized by their diverse behaviors ranging from solid-like to fluid-like and classified into different regimes. Establishment of a general frictional-collisional rheology capable of capturing the important features of dense granular flows in all regimes from quasi-static to inertial is known to be important from a practical point of view. The present study suggests a rheological model that includes both collisional and frictional mechanisms in dense granular flows by adding the effect of persistent contact between granular particles into the classical kinetic theory. The kinetic theory is used to formulate the collisional stresses, while the frictional stresses are modeled based on an existing relation derived by statistically averaging the individual contact forces among cohesionless particles. The proposed frictional-collisional model is then applied to steady flows of granular materials over an inclined surface, collapses of granular columns, and unsteady flows of granular materials down an inclined surface. The numerical results on the bulk behaviors of the granular flows, such as the varying profile of the free surface and the flow velocity, are all in good agreement with available experimental data. It is shown that the proposed rheological model can well describe the entire processes of dense granular flows from initiation to final deposit or fully developed steady state. Its broad applicability to various granular flows can thus be expected.