A Multi-Phase Mass Flow Model

Geomorphic mass flows are often complex in terms of material composition and its evolution in space and time. The simulation of those hazardous phenomena would strongly benefit from a multi-phase model, considering the motion and-importantly-interaction of phases characterized by different physical aspects including densities, frictions, viscosities, fractions, and their mechanical responses. However, such a genuine multi-phase model is still lacking. Here, we present a first-ever, multi-mechanical, multi-phase mass flow model composed of three different phases: the coarse solid fraction, fine-solid fraction, and viscous fluid. The coarse solid component, called solid, represents boulders, cobbles, gravels, or blocks of ice. Fine-solid represents fine particles and sand, whereas water and very fine particles, including colloids, silt, and clay, constitute the viscous fluid component in the mixture. The involved materials display distinct mechanical responses and dynamic behaviors. Therefore, the solid, fine-solid, and fluid phases are described by Coulomb-plastic, shear- and pressure-dependent plasticity-dominated viscoplastic, and viscosity-dominated viscoplastic rheologies. They are supposed to best represent those materials. The new model is flexible and addresses some long-standing issues of multi-phase mass flows on how to reliably describe the flow dynamics, runout, and deposition morphology of such type of phenomena. With reference to some benchmark simulations, the essence of the model and its applicability are discussed.